Java/Collections Data Structure/ArrayList
Содержание
- 1 A boolean is being stored and then retrieved from an ArrayList
- 2 Add an element to specified index of Java ArrayList
- 3 Append all elements of other Collection to Java ArrayList
- 4 A variant of java.util.ArrayList in which all mutative operations (add, set, and so on) are implemented by making a fresh copy of the underlying array
- 5 Convert a List (ArrayList) to an Array with full length array
- 6 Convert a List (ArrayList) to an Array with zero length array
- 7 Convert an ArrayList into an array.
- 8 Copy all elements of Java ArrayList to an Object Array
- 9 Copy Elements of ArrayList to Java Vector
- 10 Copy Elements of One Java ArrayList to Another Java ArrayList
- 11 Copy On Write ArrayList
- 12 Find maximum element of Java ArrayList
- 13 Find Minimum element of Java ArrayList
- 14 Get element in an ArrayList by index
- 15 Get Enumeration over Java ArrayList
- 16 Get generic Iterator from generic ArrayList
- 17 Get Previous and next index using Java ListIterator
- 18 Get Size of Java ArrayList and loop through elements
- 19 Get Sub List of Java ArrayList
- 20 Get Synchronized List from Java ArrayList
- 21 Get the size of an arraylist after and before add and remove methods
- 22 How to Convert an ArrayList into an array
- 23 If an ArrayList contains a given item
- 24 Insert all elements of other Collection to Specified Index of Java ArrayList
- 25 Iterate through a Collection using Java Iterator
- 26 Iterate through elements Java ArrayList using Iterator
- 27 Iterate through elements Java ArrayList using ListIterator
- 28 Looping through a Collection object: while loop, iterator, and for each
- 29 pass the actual object you want removed.
- 30 Perform Binary Search on Java ArrayList
- 31 Pre-generics example that uses a collection.
- 32 Remove all elements from Java ArrayList
- 33 Remove an element from ArrayList using Java ListIterator
- 34 Remove an element from Collection using Java Iterator
- 35 Remove an element from specified index of Java ArrayList
- 36 Remove duplicate items from an ArrayList
- 37 Replace All Elements Of Java ArrayList
- 38 Replace all occurrences of specified element of Java ArrayList
- 39 Replace an element at specified index of Java ArrayList
- 40 Replace an element from ArrayList using Java ListIterator
- 41 Reverse order of all elements of Java ArrayList
- 42 Rotate elements of a collection
- 43 Search an element of Java ArrayList
- 44 Search collection element
- 45 shows the modern, generic form of collection classes
- 46 Shuffle elements of Java ArrayList
- 47 Sort elements of Java ArrayList
- 48 Sort items of an ArrayList
- 49 Sort Java ArrayList in descending order using comparator
- 50 Store user-defined objects in arraylist
- 51 Swap elements of Java ArrayList
- 52 Traverse through ArrayList in forward direction using Java ListIterator
- 53 Traverse through ArrayList in reverse direction using Java ListIterator
- 54 Use set method to change the value in an array list
- 55 Use the Iterator returned from ArrayList to loop through an array list
A boolean is being stored and then retrieved from an ArrayList
<source lang="java">
import java.util.ArrayList; public class Main {
public static void main(String... args) {
ArrayList<Boolean> list = new ArrayList<Boolean>();
list.add(true);
boolean flag = list.get(0);
}
}
</source>
Add an element to specified index of Java ArrayList
<source lang="java">
import java.util.ArrayList; public class Main {
public static void main(String[] args) {
ArrayList<String> arrayList = new ArrayList<String>();
arrayList.add("1");
arrayList.add("2");
arrayList.add("3");
arrayList.add(1, "INSERTED");
for (String str: arrayList)
System.out.println(str);
}
} /* 1 INSERTED 2 3
- /
</source>
Append all elements of other Collection to Java ArrayList
<source lang="java">
import java.util.ArrayList; import java.util.Vector; public class Main {
public static void main(String[] args) {
ArrayList<String> arrayList = new ArrayList<String>();
arrayList.add("1");
arrayList.add("2");
arrayList.add("3");
Vector<String> v = new Vector<String>();
v.add("4");
v.add("5");
// append all elements of Vector to ArrayList
arrayList.addAll(v);
for (String str : arrayList)
System.out.println(str);
}
} /* 1 2 3 4 5
- /
</source>
A variant of java.util.ArrayList in which all mutative operations (add, set, and so on) are implemented by making a fresh copy of the underlying array
<source lang="java">
/*
* File: CopyOnWriteArrayList.java
*
* Written by Doug Lea. Adapted and released, under explicit permission, from
* JDK1.2 ArrayList.java which carries the following copyright:
*
* Copyright 1997 by Sun Microsystems, Inc., 901 San Antonio Road, Palo Alto,
* California, 94303, U.S.A. All rights reserved.
*
* This software is the confidential and proprietary information of Sun
* Microsystems, Inc. ("Confidential Information"). You shall not disclose such
* Confidential Information and shall use it only in accordance with the terms
* of the license agreement you entered into with Sun.
*
* History: Date Who What 21Jun1998 dl Create public version 9Oct1999 dl faster
* equals 29jun2001 dl Serialization methods now private
*/
import java.util.*; /**
* This class implements a variant of java.util.ArrayList in which all mutative * operations (add, set, and so on) are implemented by making a fresh copy of * the underlying array.*
* This is ordinarily too costly, but it becomes attractive when traversal
* operations vastly overwhelm mutations, and, especially, when you cannot or
* don"t want to synchronize traversals, yet need to preclude interference among
* concurrent threads. The iterator method uses a reference to the state of the
* array at the point that the iterator was created. This array never changes
* during the lifetime of the iterator, so interference is impossible. (The
* iterator will not traverse elements added or changed since the iterator was
* created, but usually this is a desirable feature.)
* <p>
* As much code and documentation as possible was shamelessly copied from
* java.util.ArrayList (Thanks, Josh!), with the intent of preserving all
* semantics of ArrayList except for the copy-on-write property. (The java.util
* collection code could not be subclassed here since all of the existing
* collection classes assume elementwise mutability.)
* <p>
* Because of the copy-on-write policy, some one-by-one mutative operations in
* the java.util.Arrays and java.util.Collections classes are so time/space
* intensive as to never be worth calling (except perhaps as benchmarks for
* garbage collectors :-).
* <p>
* Three methods are supported in addition to those described in List and
* ArrayList. The addIfAbsent and addAllAbsent methods provide Set semantics for
* add, and are used in CopyOnWriteArraySet. However, they can also be used
* directly from this List version. The copyIn method (and a constructor that
* invokes it) allow you to copy in an initial array to use. This method can be
* useful when you first want to perform many operations on a plain array, and
* then make a copy available for use through the collection API.
* <p>
* Due to their strict read-only nature, element-changing operations on
* iterators (remove, set, and add) are not supported. These are the only
* methods throwing UnsupportedOperationException.
* <p>
* <p>[]
*
* @see CopyOnWriteArraySet
*/
public class CopyOnWriteArrayList implements List, Cloneable, java.io.Serializable
{
private static final long serialVersionUID = 1L;
/**
* The held array. Directly access only within synchronized methods
*/
protected transient Object[] array_;
/**
* Accessor to the array intended to be called from within unsynchronized
* read-only methods
*
* @return The internal array
*/
protected synchronized Object[] array()
{
return array_;
}
/**
* Constructs an empty list
*
*/
public CopyOnWriteArrayList()
{
array_ = new Object[0];
}
/**
* Constructs an list containing the elements of the specified Collection,
* in the order they are returned by the Collection"s iterator.
*
* @param c The collection to get the objects from.
*/
public CopyOnWriteArrayList(Collection c)
{
array_ = new Object[c.size()];
Iterator i = c.iterator();
int size = 0;
while (i.hasNext())
array_[size++] = i.next();
}
/**
* Create a new CopyOnWriteArrayList holding a copy of given array
*
* @param toCopyIn
* the array. A copy of this array is used as the internal array.
*/
public CopyOnWriteArrayList(Object[] toCopyIn)
{
copyIn(toCopyIn, 0, toCopyIn.length);
}
/**
* Replace the held array with a copy of the n elements of
* the provided array, starting at position first. To copy
* an entire array, call with arguments (array, 0, array.length).
*
* @param toCopyIn
* the array. A copy of the indicated elements of this array is
* used as the internal array.
* @param first
* The index of first position of the array to start copying
* from.
* @param n
* the number of elements to copy. This will be the new size of
* the list.
*/
public synchronized void copyIn(Object[] toCopyIn, int first, int n)
{
array_ = new Object[n];
System.arraycopy(toCopyIn, first, array_, 0, n);
}
/**
* Returns the number of components in this list.
*
* @return the number of components in this list.
*/
public int size()
{
return array().length;
}
/**
* Tests if this list has no components.
*
* @return true if this list has no components;
* false otherwise.
*/
public boolean isEmpty()
{
return size() == 0;
}
/**
* Returns true if this list contains the specified element.
*
* @param o
* element whose presence in this List is to be tested.
*/
public boolean contains(Object elem)
{
Object[] elementData = array();
int len = elementData.length;
return indexOf(elem, elementData, len) >= 0;
}
/**
* Searches for the first occurence of the given argument, testing for
* equality using the equals method.
*
* @param elem
* an object.
* @return the index of the first occurrence of the argument in this list;
* returns -1 if the object is not found.
* @see Object#equals(Object)
*/
public int indexOf(Object elem)
{
Object[] elementData = array();
int len = elementData.length;
return indexOf(elem, elementData, len);
}
/**
* static version allows repeated call without needed to grab lock for array
* each time
* @param elem
* @param elementData
* @param len
* @return The index that is found. -1 if not found
*/
protected static int indexOf(Object elem, Object[] elementData, int len)
{
if (elem == null)
{
for (int i = 0; i < len; i++)
if (elementData[i] == null)
return i;
}
else
{
for (int i = 0; i < len; i++)
if (elem.equals(elementData[i]))
return i;
}
return -1;
}
/**
* Searches for the first occurence of the given argument, beginning the
* search at index, and testing for equality using the
* equals method.
*
* @param elem
* an object.
* @param index
* the index to start searching from.
* @return the index of the first occurrence of the object argument in this
* List at position index or later in the List;
* returns -1 if the object is not found.
* @see Object#equals(Object)
*/
// needed in order to compile on 1.2b3
public int indexOf(Object elem, int index)
{
Object[] elementData = array();
int elementCount = elementData.length;
if (elem == null)
{
for (int i = index; i < elementCount; i++)
if (elementData[i] == null)
return i;
}
else
{
for (int i = index; i < elementCount; i++)
if (elem.equals(elementData[i]))
return i;
}
return -1;
}
/**
* Returns the index of the last occurrence of the specified object in this
* list.
*
* @param elem
* the desired component.
* @return the index of the last occurrence of the specified object in this
* list; returns -1 if the object is not found.
*/
public int lastIndexOf(Object elem)
{
Object[] elementData = array();
int len = elementData.length;
return lastIndexOf(elem, elementData, len);
}
protected static int lastIndexOf(Object elem, Object[] elementData, int len)
{
if (elem == null)
{
for (int i = len - 1; i >= 0; i--)
if (elementData[i] == null)
return i;
}
else
{
for (int i = len - 1; i >= 0; i--)
if (elem.equals(elementData[i]))
return i;
}
return -1;
}
/**
* Searches backwards for the specified object, starting from the specified
* index, and returns an index to it.
*
* @param elem
* the desired component.
* @param index
* the index to start searching from.
* @return the index of the last occurrence of the specified object in this
* List at position less than index in the List; -1 if the object is
* not found.
*/
public int lastIndexOf(Object elem, int index)
{
// needed in order to compile on 1.2b3
Object[] elementData = array();
if (elem == null)
{
for (int i = index; i >= 0; i--)
if (elementData[i] == null)
return i;
}
else
{
for (int i = index; i >= 0; i--)
if (elem.equals(elementData[i]))
return i;
}
return -1;
}
/**
* Returns a shallow copy of this list. (The elements themselves are not
* copied.)
*
* @return a clone of this list.
*/
public Object clone()
{
try
{
Object[] elementData = array();
CopyOnWriteArrayList v = (CopyOnWriteArrayList)super.clone();
v.array_ = new Object[elementData.length];
System.arraycopy(elementData, 0, v.array_, 0, elementData.length);
return v;
}
catch (CloneNotSupportedException e)
{
// this shouldn"t happen, since we are Cloneable
throw new InternalError();
}
}
/**
* Returns an array containing all of the elements in this list in the
* correct order.
*/
public Object[] toArray()
{
Object[] elementData = array();
Object[] result = new Object[elementData.length];
System.arraycopy(elementData, 0, result, 0, elementData.length);
return result;
}
/**
* Returns an array containing all of the elements in this list in the
* correct order. The runtime type of the returned array is that of the
* specified array. If the list fits in the specified array, it is returned
* therein. Otherwise, a new array is allocated with the runtime type of the
* specified array and the size of this list.
* <p>
* If the list fits in the specified array with room to spare (i.e., the
* array has more elements than the list), the element in the array
* immediately following the end of the collection is set to null. This is
* useful in determining the length of the list only if the
* caller knows that the list does not contain any null elements.
*
* @param a
* the array into which the elements of the list are to be
* stored, if it is big enough; otherwise, a new array of the
* same runtime type is allocated for this purpose.
* @return an array containing the elements of the list.
* @exception ArrayStoreException
* the runtime type of a is not a supertype of the runtime
* type of every element in this list.
*/
public Object[] toArray(Object a[])
{
Object[] elementData = array();
if (a.length < elementData.length)
a = (Object[])java.lang.reflect.Array.newInstance(a.getClass().getComponentType(),
elementData.length);
System.arraycopy(elementData, 0, a, 0, elementData.length);
if (a.length > elementData.length)
a[elementData.length] = null;
return a;
}
// Positional Access Operations
/**
* Returns the element at the specified position in this list.
*
* @param index
* index of element to return.
* @exception IndexOutOfBoundsException
* index is out of range (index < 0 || index >=
* size()).
*/
public Object get(int index)
{
Object[] elementData = array();
rangeCheck(index, elementData.length);
return elementData[index];
}
/**
* Replaces the element at the specified position in this list with the
* specified element.
*
* @param index
* index of element to replace.
* @param element
* element to be stored at the specified position.
* @return the element previously at the specified position.
* @exception IndexOutOfBoundsException
* index out of range (index < 0 || index >= size()).
*/
public synchronized Object set(int index, Object element)
{
int len = array_.length;
rangeCheck(index, len);
Object oldValue = array_[index];
boolean same = (oldValue == element || (element != null && element.equals(oldValue)));
if (!same)
{
Object[] newArray = new Object[len];
System.arraycopy(array_, 0, newArray, 0, len);
newArray[index] = element;
array_ = newArray;
}
return oldValue;
}
/**
* Appends the specified element to the end of this list.
*
* @param element
* element to be appended to this list.
* @return true (as per the general contract of Collection.add).
*/
public synchronized boolean add(Object element)
{
int len = array_.length;
Object[] newArray = new Object[len + 1];
System.arraycopy(array_, 0, newArray, 0, len);
newArray[len] = element;
array_ = newArray;
return true;
}
/**
* Inserts the specified element at the specified position in this list.
* Shifts the element currently at that position (if any) and any subsequent
* elements to the right (adds one to their indices).
*
* @param index
* index at which the specified element is to be inserted.
* @param element
* element to be inserted.
* @exception IndexOutOfBoundsException
* index is out of range (index < 0 || index > size()).
*/
public synchronized void add(int index, Object element)
{
int len = array_.length;
if (index > len || index < 0)
throw new IndexOutOfBoundsException("Index: " + index + ", Size: " + len);
Object[] newArray = new Object[len + 1];
System.arraycopy(array_, 0, newArray, 0, index);
newArray[index] = element;
System.arraycopy(array_, index, newArray, index + 1, len - index);
array_ = newArray;
}
/**
* Removes the element at the specified position in this list. Shifts any
* subsequent elements to the left (subtracts one from their indices).
* Returns the element that was removed from the list.
*
* @param index
* the index of the element to removed.
* @exception IndexOutOfBoundsException
* index out of range (index < 0 || index >= size()).
*/
public synchronized Object remove(int index)
{
int len = array_.length;
rangeCheck(index, len);
Object oldValue = array_[index];
Object[] newArray = new Object[len - 1];
System.arraycopy(array_, 0, newArray, 0, index);
int numMoved = len - index - 1;
if (numMoved > 0)
System.arraycopy(array_, index + 1, newArray, index, numMoved);
array_ = newArray;
return oldValue;
}
/**
* Removes a single instance of the specified element from this Collection,
* if it is present (optional operation). More formally, removes an element
* e such that (o==null ? e==null :
* o.equals(e)),
* if the Collection contains one or more such elements. Returns true if the
* Collection contained the specified element (or equivalently, if the
* Collection changed as a result of the call).
*
* @param element
* element to be removed from this Collection, if present.
* @return true if the Collection changed as a result of the call.
*/
public synchronized boolean remove(Object element)
{
int len = array_.length;
if (len == 0)
return false;
// Copy while searching for element to remove
// This wins in the normal case of element being present
int newlen = len - 1;
Object[] newArray = new Object[newlen];
for (int i = 0; i < newlen; ++i)
{
if (element == array_[i] || (element != null && element.equals(array_[i])))
{
// found one; copy remaining and exit
for (int k = i + 1; k < len; ++k)
newArray[k - 1] = array_[k];
array_ = newArray;
return true;
}
else
newArray[i] = array_[i];
}
// special handling for last cell
if (element == array_[newlen] || (element != null && element.equals(array_[newlen])))
{
array_ = newArray;
return true;
}
else
return false; // throw away copy
}
/**
* Removes from this List all of the elements whose index is between
* fromIndex, inclusive and toIndex, exclusive. Shifts any succeeding
* elements to the left (reduces their index). This call shortens the List
* by (toIndex - fromIndex) elements. (If toIndex==fromIndex, this operation
* has no effect.)
*
* @param fromIndex
* index of first element to be removed.
* @param toIndex
* index after last element to be removed.
* @exception IndexOutOfBoundsException
* fromIndex or toIndex out of range (fromIndex < 0 ||
* fromIndex >= size() || toIndex > size() || toIndex
* < fromIndex).
*/
public synchronized void removeRange(int fromIndex, int toIndex)
{
int len = array_.length;
if (fromIndex < 0 || fromIndex >= len || toIndex > len || toIndex < fromIndex)
throw new IndexOutOfBoundsException();
int numMoved = len - toIndex;
int newlen = len - (toIndex - fromIndex);
Object[] newArray = new Object[newlen];
System.arraycopy(array_, 0, newArray, 0, fromIndex);
System.arraycopy(array_, toIndex, newArray, fromIndex, numMoved);
array_ = newArray;
}
/**
* Append the element if not present. This operation can be used to obtain
* Set semantics for lists.
*
* @param element
* element to be added to this Collection, if absent.
* @return true if added
*/
public synchronized boolean addIfAbsent(Object element)
{
// Copy while checking if already present.
// This wins in the most common case where it is not present
int len = array_.length;
Object[] newArray = new Object[len + 1];
for (int i = 0; i < len; ++i)
{
if (element == array_[i] || (element != null && element.equals(array_[i])))
return false; // exit, throwing away copy
else
newArray[i] = array_[i];
}
newArray[len] = element;
array_ = newArray;
return true;
}
/**
* Returns true if this Collection contains all of the elements in the
* specified Collection.
* <p>
* This implementation iterates over the specified Collection, checking each
* element returned by the Iterator in turn to see if it"s contained in this
* Collection. If all elements are so contained true is returned, otherwise
* false.
*
*/
public boolean containsAll(Collection c)
{
Object[] elementData = array();
int len = elementData.length;
Iterator e = c.iterator();
while (e.hasNext())
if (indexOf(e.next(), elementData, len) < 0)
return false;
return true;
}
/**
* Removes from this Collection all of its elements that are contained in
* the specified Collection. This is a particularly expensive operation in
* this class because of the need for an internal temporary array.
* <p>
*
* @return true if this Collection changed as a result of the call.
*/
public synchronized boolean removeAll(Collection c)
{
Object[] elementData = array_;
int len = elementData.length;
if (len == 0)
return false;
// temp array holds those elements we know we want to keep
Object[] temp = new Object[len];
int newlen = 0;
for (int i = 0; i < len; ++i)
{
Object element = elementData[i];
if (!c.contains(element))
{
temp[newlen++] = element;
}
}
if (newlen == len)
return false;
// copy temp as new array
Object[] newArray = new Object[newlen];
System.arraycopy(temp, 0, newArray, 0, newlen);
array_ = newArray;
return true;
}
/**
* Retains only the elements in this Collection that are contained in the
* specified Collection (optional operation). In other words, removes from
* this Collection all of its elements that are not contained in the
* specified Collection.
*
* @return true if this Collection changed as a result of the call.
*/
public synchronized boolean retainAll(Collection c)
{
Object[] elementData = array_;
int len = elementData.length;
if (len == 0)
return false;
Object[] temp = new Object[len];
int newlen = 0;
for (int i = 0; i < len; ++i)
{
Object element = elementData[i];
if (c.contains(element))
{
temp[newlen++] = element;
}
}
if (newlen == len)
return false;
Object[] newArray = new Object[newlen];
System.arraycopy(temp, 0, newArray, 0, newlen);
array_ = newArray;
return true;
}
/**
* Appends all of the elements in the specified Collection that are not
* already contained in this list, to the end of this list, in the order
* that they are returned by the specified Collection"s Iterator.
*
* @param c
* elements to be added into this list.
* @return the number of elements added
*/
public synchronized int addAllAbsent(Collection c)
{
int numNew = c.size();
if (numNew == 0)
return 0;
Object[] elementData = array_;
int len = elementData.length;
Object[] temp = new Object[numNew];
int added = 0;
Iterator e = c.iterator();
while (e.hasNext())
{
Object element = e.next();
if (indexOf(element, elementData, len) < 0)
{
if (indexOf(element, temp, added) < 0)
{
temp[added++] = element;
}
}
}
if (added == 0)
return 0;
Object[] newArray = new Object[len + added];
System.arraycopy(elementData, 0, newArray, 0, len);
System.arraycopy(temp, 0, newArray, len, added);
array_ = newArray;
return added;
}
/**
* Removes all of the elements from this list.
*
*/
public synchronized void clear()
{
array_ = new Object[0];
}
/**
* Appends all of the elements in the specified Collection to the end of
* this list, in the order that they are returned by the specified
* Collection"s Iterator.
*
* @param c
* elements to be inserted into this list.
*/
public synchronized boolean addAll(Collection c)
{
int numNew = c.size();
if (numNew == 0)
return false;
int len = array_.length;
Object[] newArray = new Object[len + numNew];
System.arraycopy(array_, 0, newArray, 0, len);
Iterator e = c.iterator();
for (int i = 0; i < numNew; i++)
newArray[len++] = e.next();
array_ = newArray;
return true;
}
/**
* Inserts all of the elements in the specified Collection into this list,
* starting at the specified position. Shifts the element currently at that
* position (if any) and any subsequent elements to the right (increases
* their indices). The new elements will appear in the list in the order
* that they are returned by the specified Collection"s iterator.
*
* @param index
* index at which to insert first element from the specified
* collection.
* @param c
* elements to be inserted into this list.
* @exception IndexOutOfBoundsException
* index out of range (index < 0 || index > size()).
*/
public synchronized boolean addAll(int index, Collection c)
{
int len = array_.length;
if (index > len || index < 0)
throw new IndexOutOfBoundsException("Index: " + index + ", Size: " + len);
int numNew = c.size();
if (numNew == 0)
return false;
Object[] newArray = new Object[len + numNew];
System.arraycopy(array_, 0, newArray, 0, len);
int numMoved = len - index;
if (numMoved > 0)
System.arraycopy(array_, index, newArray, index + numNew, numMoved);
Iterator e = c.iterator();
for (int i = 0; i < numNew; i++)
newArray[index++] = e.next();
array_ = newArray;
return true;
}
/**
* Check if the given index is in range. If not, throw an appropriate
* runtime exception.
* @param index
* @param length
*/
protected void rangeCheck(int index, int length)
{
if (index >= length || index < 0)
throw new IndexOutOfBoundsException("Index: " + index + ", Size: " + length);
}
/**
* Save the state of the list to a stream (i.e., serialize it).
* @param s
* @throws java.io.IOException
*
* @serialData The length of the array backing the list is emitted (int),
* followed by all of its elements (each an Object) in the
* proper order.
*/
private void writeObject(java.io.ObjectOutputStream s) throws java.io.IOException
{
// Write out element count, and any hidden stuff
s.defaultWriteObject();
Object[] elementData = array();
// Write out array length
s.writeInt(elementData.length);
// Write out all elements in the proper order.
for (int i = 0; i < elementData.length; i++)
s.writeObject(elementData[i]);
}
/**
* Reconstitute the list from a stream (i.e., deserialize it).
* @param s
* @throws java.io.IOException
* @throws ClassNotFoundException
*/
private synchronized void readObject(java.io.ObjectInputStream s) throws java.io.IOException,
ClassNotFoundException
{
// Read in size, and any hidden stuff
s.defaultReadObject();
// Read in array length and allocate array
int arrayLength = s.readInt();
Object[] elementData = new Object[arrayLength];
// Read in all elements in the proper order.
for (int i = 0; i < elementData.length; i++)
elementData[i] = s.readObject();
array_ = elementData;
}
/**
* Returns a string representation of this Collection, containing the String
* representation of each element.
*/
public String toString()
{
StringBuffer buf = new StringBuffer();
Iterator e = iterator();
buf.append("[");
int maxIndex = size() - 1;
for (int i = 0; i <= maxIndex; i++)
{
buf.append(String.valueOf(e.next()));
if (i < maxIndex)
buf.append(", ");
}
buf.append("]");
return buf.toString();
}
/**
* Compares the specified Object with this List for equality. Returns true
* if and only if the specified Object is also a List, both Lists have the
* same size, and all corresponding pairs of elements in the two Lists are
* equal. (Two elements e1 and e2
* are equal if
* (e1==null ? e2==null : e1.equals(e2)).) In other words,
* two Lists are defined to be equal if they contain the same elements in
* the same order.
* <p>
* This implementation first checks if the specified object is this List. If
* so, it returns true; if not, it checks if the specified object is a List.
* If not, it returns false; if so, it iterates over both lists, comparing
* corresponding pairs of elements. If any comparison returns false, this
* method returns false. If either Iterator runs out of elements before
* before the other it returns false (as the Lists are of unequal length);
* otherwise it returns true when the iterations complete.
*
* @param o
* the Object to be compared for equality with this List.
* @return true if the specified Object is equal to this List.
*/
public boolean equals(Object o)
{
if (o == this)
return true;
if (!(o instanceof List))
return false;
List l2 = (List)(o);
if (size() != l2.size())
return false;
ListIterator e1 = listIterator();
ListIterator e2 = l2.listIterator();
while (e1.hasNext())
{
Object o1 = e1.next();
Object o2 = e2.next();
if (!(o1 == null ? o2 == null : o1.equals(o2)))
return false;
}
return true;
}
/**
* Returns the hash code value for this List.
* <p>
* This implementation uses exactly the code that is used to define the List
* hash function in the documentation for List.hashCode.
*/
public int hashCode()
{
int hashCode = 1;
Iterator i = iterator();
while (i.hasNext())
{
Object obj = i.next();
hashCode = 31 * hashCode + (obj == null ? 0 : obj.hashCode());
}
return hashCode;
}
/**
* Returns an Iterator over the elements contained in this collection. The
* iterator provides a snapshot of the state of the list when the iterator
* was constructed. No synchronization is needed while traversing the
* iterator. The iterator does NOT support the
* remove method.
*/
public Iterator iterator()
{
return new COWIterator(array(), 0);
}
/**
* Returns an Iterator of the elements in this List (in proper sequence).
* The iterator provides a snapshot of the state of the list when the
* iterator was constructed. No synchronization is needed while traversing
* the iterator. The iterator does NOT support the
* remove, set, or add
* methods.
*
*/
public ListIterator listIterator()
{
return new COWIterator(array(), 0);
}
/**
* Returns a ListIterator of the elements in this List (in proper sequence),
* starting at the specified position in the List. The specified index
* indicates the first element that would be returned by an initial call to
* nextElement. An initial call to previousElement would return the element
* with the specified index minus one. The ListIterator returned by this
* implementation will throw an UnsupportedOperationException in its remove,
* set and add methods.
*
* @param index
* index of first element to be returned from the ListIterator
* (by a call to getNext).
* @exception IndexOutOfBoundsException
* index is out of range (index < 0 || index > size()).
*/
public ListIterator listIterator(final int index)
{
Object[] elementData = array();
int len = elementData.length;
if (index < 0 || index > len)
throw new IndexOutOfBoundsException("Index: " + index);
return new COWIterator(array(), index);
}
protected static class COWIterator implements ListIterator
{
/** Snapshot of the array * */
protected final Object[] array;
/**
* Index of element to be returned by subsequent call to next.
*/
protected int cursor;
protected COWIterator(Object[] elementArray, int initialCursor)
{
array = elementArray;
cursor = initialCursor;
}
public boolean hasNext()
{
return cursor < array.length;
}
public boolean hasPrevious()
{
return cursor > 0;
}
public Object next()
{
try
{
return array[cursor++];
}
catch (IndexOutOfBoundsException ex)
{
throw new NoSuchElementException();
}
}
public Object previous()
{
try
{
return array[--cursor];
}
catch (IndexOutOfBoundsException e)
{
throw new NoSuchElementException();
}
}
public int nextIndex()
{
return cursor;
}
public int previousIndex()
{
return cursor - 1;
}
/**
* Not supported. Always throws UnsupportedOperationException.
*
* @exception UnsupportedOperationException
* remove is not supported by this Iterator.
*/
public void remove()
{
throw new UnsupportedOperationException();
}
/**
* Not supported. Always throws UnsupportedOperationException.
*
* @exception UnsupportedOperationException
* set is not supported by this Iterator.
*/
public void set(Object o)
{
throw new UnsupportedOperationException();
}
/**
* Not supported. Always throws UnsupportedOperationException.
*
* @exception UnsupportedOperationException
* add is not supported by this Iterator.
*/
public void add(Object o)
{
throw new UnsupportedOperationException();
}
}
/**
* Returns a view of the portion of this List between fromIndex, inclusive,
* and toIndex, exclusive. The returned List is backed by this List, so
* changes in the returned List are reflected in this List, and vice-versa.
* While mutative operations are supported, they are probably not very
* useful for CopyOnWriteArrays.
*
* The semantics of the List returned by this method become undefined if the
* backing list (i.e., this List) is structurally modified in any
* way other than via the returned List. (Structural modifications are those
* that change the size of the List, or otherwise perturb it in such a
* fashion that iterations in progress may yield incorrect results.)
*
* @param fromIndex
* low endpoint (inclusive) of the subList.
* @param toKey
* high endpoint (exclusive) of the subList.
* @return a view of the specified range within this List.
* @exception IndexOutOfBoundsException
* Illegal endpoint index value (fromIndex < 0 || toIndex
* > size || fromIndex > toIndex).
*/
public synchronized List subList(int fromIndex, int toIndex)
{
// synchronized since sublist ctor depends on it.
int len = array_.length;
if (fromIndex < 0 || toIndex > len || fromIndex > toIndex)
throw new IndexOutOfBoundsException();
return new COWSubList(this, fromIndex, toIndex);
}
protected static class COWSubList extends AbstractList
{
/*
* This is currently a bit sleazy. The class extends AbstractList merely
* for convenience, to avoid having to define addAll, etc. This doesn"t
* hurt, but is stupid and wasteful. This class does not need or use
* modCount mechanics in AbstractList, but does need to check for
* concurrent modification using similar mechanics. On each operation,
* the array that we expect the backing list to use is checked and
* updated. Since we do this for all of the base operations invoked by
* those defined in AbstractList, all is well.
*
* It"s not clear whether this is worth cleaning up. The kinds of list
* operations inherited from AbstractList are are already so slow on COW
* sublists that adding a bit more space/time doesn"t seem even
* noticeable.
*/
protected final CopyOnWriteArrayList l;
protected final int offset;
protected int size;
protected Object[] expectedArray;
protected COWSubList(CopyOnWriteArrayList list, int fromIndex, int toIndex)
{
l = list;
expectedArray = l.array();
offset = fromIndex;
size = toIndex - fromIndex;
}
// only call this holding l"s lock
protected void checkForComodification()
{
if (l.array_ != expectedArray)
throw new ConcurrentModificationException();
}
// only call this holding l"s lock
protected void rangeCheck(int index)
{
if (index < 0 || index >= size)
throw new IndexOutOfBoundsException("Index: " + index + ",Size: " + size);
}
public Object set(int index, Object element)
{
synchronized (l)
{
rangeCheck(index);
checkForComodification();
Object x = l.set(index + offset, element);
expectedArray = l.array_;
return x;
}
}
public Object get(int index)
{
synchronized (l)
{
rangeCheck(index);
checkForComodification();
return l.get(index + offset);
}
}
public int size()
{
synchronized (l)
{
checkForComodification();
return size;
}
}
public void add(int index, Object element)
{
synchronized (l)
{
checkForComodification();
if (index < 0 || index > size)
throw new IndexOutOfBoundsException();
l.add(index + offset, element);
expectedArray = l.array_;
size++;
}
}
public Object remove(int index)
{
synchronized (l)
{
rangeCheck(index);
checkForComodification();
Object result = l.remove(index + offset);
expectedArray = l.array_;
size--;
return result;
}
}
public Iterator iterator()
{
synchronized (l)
{
checkForComodification();
return new COWSubListIterator(0);
}
}
public ListIterator listIterator(final int index)
{
synchronized (l)
{
checkForComodification();
if (index < 0 || index > size)
throw new IndexOutOfBoundsException("Index: " + index + ", Size: " + size);
return new COWSubListIterator(index);
}
}
protected class COWSubListIterator implements ListIterator
{
protected final ListIterator i;
protected final int index;
protected COWSubListIterator(int index)
{
this.index = index;
i = l.listIterator(index + offset);
}
public boolean hasNext()
{
return nextIndex() < size;
}
public Object next()
{
if (hasNext())
return i.next();
else
throw new NoSuchElementException();
}
public boolean hasPrevious()
{
return previousIndex() >= 0;
}
public Object previous()
{
if (hasPrevious())
return i.previous();
else
throw new NoSuchElementException();
}
public int nextIndex()
{
return i.nextIndex() - offset;
}
public int previousIndex()
{
return i.previousIndex() - offset;
}
public void remove()
{
throw new UnsupportedOperationException();
}
public void set(Object o)
{
throw new UnsupportedOperationException();
}
public void add(Object o)
{
throw new UnsupportedOperationException();
}
}
public List subList(int fromIndex, int toIndex)
{
synchronized (l)
{
checkForComodification();
if (fromIndex < 0 || toIndex > size)
throw new IndexOutOfBoundsException();
return new COWSubList(l, fromIndex + offset, toIndex + offset);
}
}
}
}
</source>
Convert a List (ArrayList) to an Array with full length array
<source lang="java">
import java.util.ArrayList; import java.util.List; public class Main {
public static void main(String[] args) {
List<String> carList = new ArrayList<String>();
carList.add("A");
carList.add("B");
carList.add("C");
carList.add("D");
String[] carArray = carList.toArray(new String[0]);
for (String car : carArray) {
System.out.println(car);
}
}
} /* A B C D
- /
</source>
Convert a List (ArrayList) to an Array with zero length array
<source lang="java">
import java.util.ArrayList; import java.util.List; public class Main {
public static void main(String[] args) {
List<String> carList = new ArrayList<String>();
carList.add("A");
carList.add("B");
carList.add("C");
carList.add("D");
String[] carArray = carList.toArray(new String[0]);
for (String car : carArray) {
System.out.println(car);
}
}
} /* A B C D
- /
</source>
Convert an ArrayList into an array.
<source lang="java">
import java.util.ArrayList; class ArrayListToArray {
public static void main(String args[]) {
ArrayList<Integer> al = new ArrayList<Integer>();
al.add(1);
al.add(2);
al.add(3);
al.add(4);
System.out.println("Contents of al: " + al);
Integer ia[] = new Integer[al.size()];
ia = al.toArray(ia);
int sum = 0;
for (int i : ia)
sum += i;
System.out.println("Sum is: " + sum);
}
}
</source>
Copy all elements of Java ArrayList to an Object Array
<source lang="java">
import java.util.ArrayList; public class Main {
public static void main(String[] args) {
ArrayList<String> arrayList = new ArrayList<String>();
arrayList.add("1");
arrayList.add("2");
arrayList.add("3");
arrayList.add("4");
arrayList.add("5");
Object[] objArray = arrayList.toArray();
for (Object obj : objArray)
System.out.println(obj);
}
}
</source>
Copy Elements of ArrayList to Java Vector
<source lang="java">
import java.util.ArrayList; import java.util.Collections; import java.util.Vector; public class Main {
public static void main(String[] args) {
ArrayList<String> arrayList = new ArrayList<String>();
arrayList.add("1");
arrayList.add("2");
arrayList.add("3");
arrayList.add("4");
arrayList.add("5");
Vector<String> v = new Vector<String>();
v.add("A");
v.add("B");
v.add("D");
v.add("E");
v.add("F");
v.add("G");
v.add("H");
System.out.println(v);
Collections.copy(v, arrayList);
System.out.println(v);
}
} /* [A, B, D, E, F, G, H] [1, 2, 3, 4, 5, G, H]
- /
</source>
Copy Elements of One Java ArrayList to Another Java ArrayList
<source lang="java">
import java.util.ArrayList; import java.util.Collections; public class Main {
public static void main(String[] args) {
ArrayList<String> arrayList1 = new ArrayList<String>();
arrayList1.add("1");
arrayList1.add("2");
arrayList1.add("3");
ArrayList<String> arrayList2 = new ArrayList<String>();
arrayList2.add("One");
arrayList2.add("Two");
arrayList2.add("Three");
arrayList2.add("Four");
arrayList2.add("Five");
System.out.println(arrayList2);
Collections.copy(arrayList2, arrayList1);
System.out.println(arrayList2);
}
} /* [One, Two, Three, Four, Five] [1, 2, 3, Four, Five]
- /
</source>
Copy On Write ArrayList
<source lang="java">
/*
* Written by Doug Lea with assistance from members of JCP JSR-166
* Expert Group. Adapted and released, under explicit permission,
* from JDK ArrayList.java which carries the following copyright:
*
* Copyright 1997 by Sun Microsystems, Inc.,
* 901 San Antonio Road, Palo Alto, California, 94303, U.S.A.
* All rights reserved.
*
* This software is the confidential and proprietary information
* of Sun Microsystems, Inc. ("Confidential Information"). You
* shall not disclose such Confidential Information and shall use
* it only in accordance with the terms of the license agreement
* you entered into with Sun.
*/
import java.util.AbstractList; import java.util.Collection; import java.util.ConcurrentModificationException; import java.util.Iterator; import java.util.List; import java.util.ListIterator; import java.util.NoSuchElementException; import java.util.RandomAccess;
/**
* A thread-safe variant of {@link java.util.ArrayList} in which all mutative
* operations (add, set, and so on) are implemented by
* making a fresh copy of the underlying array.
*
* This is ordinarily too costly, but may be more efficient * than alternatives when traversal operations vastly outnumber * mutations, and is useful when you cannot or don"t want to * synchronize traversals, yet need to preclude interference among * concurrent threads. The "snapshot" style iterator method uses a * reference to the state of the array at the point that the iterator * was created. This array never changes during the lifetime of the * iterator, so interference is impossible and the iterator is * guaranteed not to throw ConcurrentModificationException. * The iterator will not reflect additions, removals, or changes to * the list since the iterator was created. Element-changing * operations on iterators themselves (remove, set, and * add) are not supported. These methods throw * UnsupportedOperationException. * * <p>All elements are permitted, including null. * * <p>This class is a member of the * . * * @since 1.5 * @author Doug Lea */ public class CopyOnWriteArrayList implements List, RandomAccess, Cloneable, java.io.Serializable { private static final long serialVersionUID = 8673264195747942595L; /** The array, accessed only via getArray/setArray. */ private volatile transient Object[] array; /** * This has been made public to support more efficient iteration. * DO NOT MODIFY this array upon getting it. * Otherwise you risk wreaking havoc on your list. In fact, if you are * not the author of this comment, you probably shouldn"t use it at all. * @return this lists internal array */ public Object[] getArray() { return array; } void setArray(Object[] a) { array = a; } /** * Creates an empty list. */ public CopyOnWriteArrayList() { setArray(new Object[0]); } /** * Creates a list containing the elements of the specified * collection, in the order they are returned by the collection"s * iterator. * * @param c the collection of initially held elements * @throws NullPointerException if the specified collection is null */ public CopyOnWriteArrayList(Collection c) { Object[] elements = new Object[c.size()]; int size = 0; for (Iterator itr = c.iterator(); itr.hasNext(); ) { Object e = itr.next(); elements[size++] = e; } setArray(elements); } /** * Creates a list holding a copy of the given array. * * @param toCopyIn the array (a copy of this array is used as the * internal array) * @throws NullPointerException if the specified array is null */ public CopyOnWriteArrayList(Object[] toCopyIn) { copyIn(toCopyIn, 0, toCopyIn.length); } /** * Replaces the held array with a copy of the n elements * of the provided array, starting at position first. To * copy an entire array, call with arguments (array, 0, * array.length). * @param toCopyIn the array. A copy of the indicated elements of * this array is used as the internal array. * @param first The index of first position of the array to * start copying from. * @param n the number of elements to copy. This will be the new size of * the list. */ private void copyIn(Object[] toCopyIn, int first, int n) { int limit = first + n; if (limit > toCopyIn.length) throw new IndexOutOfBoundsException(); Object[] newElements = copyOfRange(toCopyIn, first, limit, Object[].class); synchronized (this) { setArray(newElements); } } /** * Returns the number of elements in this list. * * @return the number of elements in this list */ public int size() { return getArray().length; } /** * Returns true if this list contains no elements. * * @return true if this list contains no elements */ public boolean isEmpty() { return size() == 0; } /** * Test for equality, coping with nulls. */ private static boolean eq(Object o1, Object o2) { return (o1 == null ? o2 == null : o1.equals(o2)); } /** * static version of indexOf, to allow repeated calls without * needing to re-acquire array each time. * @param o element to search for * @param elements the array * @param index first index to search * @param fence one past last index to search * @return index of element, or -1 if absent */ private static int indexOf(Object o, Object[] elements, int index, int fence) { if (o == null) { for (int i = index; i < fence; i++) if (elements[i] == null) return i; } else { for (int i = index; i < fence; i++) if (o.equals(elements[i])) return i; } return -1; } /** * static version of lastIndexOf. * @param o element to search for * @param elements the array * @param index first index to search * @return index of element, or -1 if absent */ private static int lastIndexOf(Object o, Object[] elements, int index) { if (o == null) { for (int i = index; i >= 0; i--) if (elements[i] == null) return i; } else { for (int i = index; i >= 0; i--) if (o.equals(elements[i])) return i; } return -1; } /** * Returns true if this list contains the specified element. * More formally, returns true if and only if this list contains * at least one element e such that * (o==null ? e==null : o.equals(e)). * * @param o element whose presence in this list is to be tested * @return true if this list contains the specified element */ public boolean contains(Object o) { Object[] elements = getArray(); return indexOf(o, elements, 0, elements.length) >= 0; } /** * {@inheritDoc} */ public int indexOf(Object o) { Object[] elements = getArray(); return indexOf(o, elements, 0, elements.length); } /** * Returns the index of the first occurrence of the specified element in * this list, searching forwards from index, or returns -1 if * the element is not found. * More formally, returns the lowest index i such that * (i >= index && (e==null ? get(i)==null : e.equals(get(i)))), * or -1 if there is no such index. * * @param e element to search for * @param index index to start searching from * @return the index of the first occurrence of the element in * this list at position index or later in the list; * -1 if the element is not found. * @throws IndexOutOfBoundsException if the specified index is negative */ public int indexOf(Object e, int index) { Object[] elements = getArray(); return indexOf(e, elements, index, elements.length); } /** * {@inheritDoc} */ public int lastIndexOf(Object o) { Object[] elements = getArray(); return lastIndexOf(o, elements, elements.length - 1); } /** * Returns the index of the last occurrence of the specified element in * this list, searching backwards from index, or returns -1 if * the element is not found. * More formally, returns the highest index i such that * (i <= index && (e==null ? get(i)==null : e.equals(get(i)))), * or -1 if there is no such index. * * @param e element to search for * @param index index to start searching backwards from * @return the index of the last occurrence of the element at position * less than or equal to index in this list; * -1 if the element is not found. * @throws IndexOutOfBoundsException if the specified index is greater * than or equal to the current size of this list */ public int lastIndexOf(Object e, int index) { Object[] elements = getArray(); return lastIndexOf(e, elements, index); } /** * Returns a shallow copy of this list. (The elements themselves * are not copied.) * * @return a clone of this list */ public Object clone() { try { return super.clone(); } catch (CloneNotSupportedException e) { // this shouldn"t happen, since we are Cloneable throw new InternalError(); } } /** * Returns an array containing all of the elements in this list * in proper sequence (from first to last element). * * <p>The returned array will be "safe" in that no references to it are * maintained by this list. (In other words, this method must allocate * a new array). The caller is thus free to modify the returned array. * * <p>This method acts as bridge between array-based and collection-based * APIs. * * @return an array containing all the elements in this list */ public Object[] toArray() { Object[] elements = getArray(); return copyOf(elements, elements.length); } /** * Returns an array containing all of the elements in this list in * proper sequence (from first to last element); the runtime type of * the returned array is that of the specified array. If the list fits * in the specified array, it is returned therein. Otherwise, a new * array is allocated with the runtime type of the specified array and * the size of this list. * * <p>If this list fits in the specified array with room to spare * (i.e., the array has more elements than this list), the element in * the array immediately following the end of the list is set to * null. (This is useful in determining the length of this * list only if the caller knows that this list does not contain * any null elements.) * * <p>Like the {@link #toArray()} method, this method acts as bridge between * array-based and collection-based APIs. Further, this method allows * precise control over the runtime type of the output array, and may, * under certain circumstances, be used to save allocation costs. * * <p>Suppose x is a list known to contain only strings. * The following code can be used to dump the list into a newly * allocated array of String: * *
* String[] y = x.toArray(new String[0]);
*
* Note that toArray(new Object[0]) is identical in function to
* toArray().
*
* @param a the array into which the elements of the list are to
* be stored, if it is big enough; otherwise, a new array of the
* same runtime type is allocated for this purpose.
* @return an array containing all the elements in this list
* @throws ArrayStoreException if the runtime type of the specified array
* is not a supertype of the runtime type of every element in
* this list
* @throws NullPointerException if the specified array is null
*/
public Object[] toArray(Object a[]) {
Object[] elements = getArray();
int len = elements.length;
if (a.length < len)
return copyOf(elements, len, a.getClass());
else {
System.arraycopy(elements, 0, a, 0, len);
if (a.length > len)
a[len] = null;
return a;
}
}
// Positional Access Operations
/**
* {@inheritDoc}
*
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public Object get(int index) {
return (getArray()[index]);
}
/**
* Replaces the element at the specified position in this list with the
* specified element.
*
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public synchronized Object set(int index, Object element) {
Object[] elements = getArray();
int len = elements.length;
Object oldValue = elements[index];
if (oldValue != element) {
Object[] newElements = copyOf(elements, len);
newElements[index] = element;
setArray(newElements);
}
return oldValue;
}
/**
* Appends the specified element to the end of this list.
*
* @param e element to be appended to this list
* @return true (as per the spec for {@link Collection#add})
*/
public boolean add(Object e) {
synchronized (this) {
Object[] elements = getArray();
int len = elements.length;
Object[] newElements = copyOf(elements, len + 1);
newElements[len] = e;
setArray(newElements);
}
return true;
}
/**
* Inserts the specified element at the specified position in this
* list. Shifts the element currently at that position (if any) and
* any subsequent elements to the right (adds one to their indices).
*
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public synchronized void add(int index, Object element) {
Object[] elements = getArray();
int len = elements.length;
if (index > len || index < 0)
throw new IndexOutOfBoundsException("Index: " + index+
", Size: " + len);
Object[] newElements;
int numMoved = len - index;
if (numMoved == 0)
newElements = copyOf(elements, len + 1);
else {
newElements = new Object[len + 1];
System.arraycopy(elements, 0, newElements, 0, index);
System.arraycopy(elements, index, newElements, index + 1,
numMoved);
}
newElements[index] = element;
setArray(newElements);
}
/**
* Removes the element at the specified position in this list.
* Shifts any subsequent elements to the left (subtracts one from their
* indices). Returns the element that was removed from the list.
*
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public synchronized Object remove(int index) {
Object[] elements = getArray();
int len = elements.length;
Object oldValue = elements[index];
int numMoved = len - index - 1;
if (numMoved == 0)
setArray(copyOf(elements, len - 1));
else {
Object[] newElements = new Object[len - 1];
System.arraycopy(elements, 0, newElements, 0, index);
System.arraycopy(elements, index + 1, newElements, index,
numMoved);
setArray(newElements);
}
return oldValue;
}
/**
* Removes the first occurrence of the specified element from this list,
* if it is present. If this list does not contain the element, it is
* unchanged. More formally, removes the element with the lowest index
* i such that
* (o==null ? get(i)==null : o.equals(get(i)))
* (if such an element exists). Returns true if this list
* contained the specified element (or equivalently, if this list
* changed as a result of the call).
*
* @param o element to be removed from this list, if present
* @return true if this list contained the specified element
*/
public synchronized boolean remove(Object o) {
Object[] elements = getArray();
int len = elements.length;
if (len != 0) {
// Copy while searching for element to remove
// This wins in the normal case of element being present
int newlen = len - 1;
Object[] newElements = new Object[newlen];
for (int i = 0; i < newlen; ++i) {
if (eq(o, elements[i])) {
// found one; copy remaining and exit
for (int k = i + 1; k < len; ++k)
newElements[k-1] = elements[k];
setArray(newElements);
return true;
} else
newElements[i] = elements[i];
}
// special handling for last cell
if (eq(o, elements[newlen])) {
setArray(newElements);
return true;
}
}
return false;
}
/**
* Removes from this list all of the elements whose index is between
* fromIndex, inclusive, and toIndex, exclusive.
* Shifts any succeeding elements to the left (reduces their index).
* This call shortens the list by (toIndex - fromIndex) elements.
* (If toIndex==fromIndex, this operation has no effect.)
*
* @param fromIndex index of first element to be removed
* @param toIndex index after last element to be removed
* @throws IndexOutOfBoundsException if fromIndex or toIndex out of
* range (fromIndex < 0 || fromIndex >= size() || toIndex
* > size() || toIndex < fromIndex)
*/
private synchronized void removeRange(int fromIndex, int toIndex) {
Object[] elements = getArray();
int len = elements.length;
if (fromIndex < 0 || fromIndex >= len ||
toIndex > len || toIndex < fromIndex)
throw new IndexOutOfBoundsException();
int newlen = len - (toIndex - fromIndex);
int numMoved = len - toIndex;
if (numMoved == 0)
setArray(copyOf(elements, newlen));
else {
Object[] newElements = new Object[newlen];
System.arraycopy(elements, 0, newElements, 0, fromIndex);
System.arraycopy(elements, toIndex, newElements,
fromIndex, numMoved);
setArray(newElements);
}
}
/**
* Append the element if not present.
*
* @param e element to be added to this list, if absent
* @return true if the element was added
*/
public synchronized boolean addIfAbsent(Object e) {
// Copy while checking if already present.
// This wins in the most common case where it is not present
Object[] elements = getArray();
int len = elements.length;
Object[] newElements = new Object[len + 1];
for (int i = 0; i < len; ++i) {
if (eq(e, elements[i]))
return false; // exit, throwing away copy
else
newElements[i] = elements[i];
}
newElements[len] = e;
setArray(newElements);
return true;
}
/**
* Returns true if this list contains all of the elements of the
* specified collection.
*
* @param c collection to be checked for containment in this list
* @return true if this list contains all of the elements of the
* specified collection
* @throws NullPointerException if the specified collection is null
* @see #contains(Object)
*/
public boolean containsAll(Collection c) {
Object[] elements = getArray();
int len = elements.length;
for (Iterator itr = c.iterator(); itr.hasNext(); ) {
Object e = itr.next();
if (indexOf(e, elements, 0, len) < 0)
return false;
}
return true;
}
/**
* Removes from this list all of its elements that are contained in
* the specified collection. This is a particularly expensive operation
* in this class because of the need for an internal temporary array.
*
* @param c collection containing elements to be removed from this list
* @return true if this list changed as a result of the call
* @throws ClassCastException if the class of an element of this list
* is incompatible with the specified collection (optional)
* @throws NullPointerException if this list contains a null element and the
* specified collection does not permit null elements (optional),
* or if the specified collection is null
* @see #remove(Object)
*/
public synchronized boolean removeAll(Collection c) {
Object[] elements = getArray();
int len = elements.length;
if (len != 0) {
// temp array holds those elements we know we want to keep
int newlen = 0;
Object[] temp = new Object[len];
for (int i = 0; i < len; ++i) {
Object element = elements[i];
if (!c.contains(element))
temp[newlen++] = element;
}
if (newlen != len) {
setArray(copyOfRange(temp, 0, newlen, Object[].class));
return true;
}
}
return false;
}
/**
* Retains only the elements in this list that are contained in the
* specified collection. In other words, removes from this list all of
* its elements that are not contained in the specified collection.
*
* @param c collection containing elements to be retained in this list
* @return true if this list changed as a result of the call
* @throws ClassCastException if the class of an element of this list
* is incompatible with the specified collection (optional)
* @throws NullPointerException if this list contains a null element and the
* specified collection does not permit null elements (optional),
* or if the specified collection is null
* @see #remove(Object)
*/
public synchronized boolean retainAll(Collection c) {
Object[] elements = getArray();
int len = elements.length;
if (len != 0) {
// temp array holds those elements we know we want to keep
int newlen = 0;
Object[] temp = new Object[len];
for (int i = 0; i < len; ++i) {
Object element = elements[i];
if (c.contains(element))
temp[newlen++] = element;
}
if (newlen != len) {
setArray(copyOfRange(temp, 0, newlen, Object[].class));
return true;
}
}
return false;
}
/**
* Appends all of the elements in the specified collection that
* are not already contained in this list, to the end of
* this list, in the order that they are returned by the
* specified collection"s iterator.
*
* @param c collection containing elements to be added to this list
* @return the number of elements added
* @throws NullPointerException if the specified collection is null
* @see #addIfAbsent(Object)
*/
public int addAllAbsent(Collection c) {
int numNew = c.size();
if (numNew == 0)
return 0;
synchronized (this) {
Object[] elements = getArray();
int len = elements.length;
Object[] temp = new Object[numNew];
int added = 0;
for (Iterator itr = c.iterator(); itr.hasNext(); ) {
Object e = itr.next();
if (indexOf(e, elements, 0, len) < 0 &&
indexOf(e, temp, 0, added) < 0)
temp[added++] = e;
}
if (added != 0) {
Object[] newElements = new Object[len + added];
System.arraycopy(elements, 0, newElements, 0, len);
System.arraycopy(temp, 0, newElements, len, added);
setArray(newElements);
}
return added;
}
}
/**
* Removes all of the elements from this list.
* The list will be empty after this call returns.
*/
public synchronized void clear() {
setArray(new Object[0]);
}
/**
* Appends all of the elements in the specified collection to the end
* of this list, in the order that they are returned by the specified
* collection"s iterator.
*
* @param c collection containing elements to be added to this list
* @return true if this list changed as a result of the call
* @throws NullPointerException if the specified collection is null
* @see #add(Object)
*/
public boolean addAll(Collection c) {
int numNew = c.size();
if (numNew == 0)
return false;
synchronized (this) {
Object[] elements = getArray();
int len = elements.length;
Object[] newElements = new Object[len + numNew];
System.arraycopy(elements, 0, newElements, 0, len);
for (Iterator itr = c.iterator(); itr.hasNext(); ) {
Object e = itr.next();
newElements[len++] = e;
}
setArray(newElements);
return true;
}
}
/**
* Inserts all of the elements in the specified collection into this
* list, starting at the specified position. Shifts the element
* currently at that position (if any) and any subsequent elements to
* the right (increases their indices). The new elements will appear
* in this list in the order that they are returned by the
* specified collection"s iterator.
*
* @param index index at which to insert the first element
* from the specified collection
* @param c collection containing elements to be added to this list
* @return true if this list changed as a result of the call
* @throws IndexOutOfBoundsException {@inheritDoc}
* @throws NullPointerException if the specified collection is null
* @see #add(int,Object)
*/
public boolean addAll(int index, Collection c) {
int numNew = c.size();
synchronized (this) {
Object[] elements = getArray();
int len = elements.length;
if (index > len || index < 0)
throw new IndexOutOfBoundsException("Index: " + index +
", Size: "+ len);
if (numNew == 0)
return false;
int numMoved = len - index;
Object[] newElements;
if (numMoved == 0)
newElements = copyOf(elements, len + numNew);
else {
newElements = new Object[len + numNew];
System.arraycopy(elements, 0, newElements, 0, index);
System.arraycopy(elements, index,
newElements, index + numNew,
numMoved);
}
for (Iterator itr = c.iterator(); itr.hasNext(); ) {
Object e = itr.next();
newElements[index++] = e;
}
setArray(newElements);
return true;
}
}
/**
* Save the state of the list to a stream (i.e., serialize it).
*
* @serialData The length of the array backing the list is emitted
* (int), followed by all of its elements (each an Object)
* in the proper order.
* @param s the stream
*/
private void writeObject(java.io.ObjectOutputStream s)
throws java.io.IOException{
// Write out element count, and any hidden stuff
s.defaultWriteObject();
Object[] elements = getArray();
int len = elements.length;
// Write out array length
s.writeInt(len);
// Write out all elements in the proper order.
for (int i = 0; i < len; i++)
s.writeObject(elements[i]);
}
/**
* Reconstitute the list from a stream (i.e., deserialize it).
* @param s the stream
*/
private void readObject(java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException {
// Read in size, and any hidden stuff
s.defaultReadObject();
// Read in array length and allocate array
int len = s.readInt();
Object[] elements = new Object[len];
// Read in all elements in the proper order.
for (int i = 0; i < len; i++)
elements[i] = s.readObject();
setArray(elements);
}
/**
* Returns a string representation of this list, containing
* the String representation of each element.
*/
public String toString() {
Object[] elements = getArray();
int maxIndex = elements.length - 1;
StringBuffer buf = new StringBuffer();
buf.append("[");
for (int i = 0; i <= maxIndex; i++) {
buf.append(String.valueOf(elements[i]));
if (i < maxIndex)
buf.append(", ");
}
buf.append("]");
return buf.toString();
}
/**
* Compares the specified object with this list for equality.
* Returns true if and only if the specified object is also a {@link
* List}, both lists have the same size, and all corresponding pairs
* of elements in the two lists are equal. (Two elements
* e1 and e2 are equal if (e1==null ?
* e2==null : e1.equals(e2)).) In other words, two lists are
* defined to be equal if they contain the same elements in the same
* order.
*
* @param o the object to be compared for equality with this list
* @return true if the specified object is equal to this list
*/
public boolean equals(Object o) {
if (o == this)
return true;
if (!(o instanceof List))
return false;
List l2 = (List)(o);
if (size() != l2.size())
return false;
ListIterator e1 = listIterator();
ListIterator e2 = l2.listIterator();
while (e1.hasNext()) {
if (!eq(e1.next(), e2.next()))
return false;
}
return true;
}
/**
* Returns the hash code value for this list.
*
* <p>This implementation uses the definition in {@link List#hashCode}.
*
* @return the hash code value for this list
*/
public int hashCode() {
int hashCode = 1;
Object[] elements = getArray();
int len = elements.length;
for (int i = 0; i < len; ++i) {
Object obj = elements[i];
hashCode = 31*hashCode + (obj==null ? 0 : obj.hashCode());
}
return hashCode;
}
/**
* Returns an iterator over the elements in this list in proper sequence.
*
* <p>The returned iterator provides a snapshot of the state of the list
* when the iterator was constructed. No synchronization is needed while
* traversing the iterator. The iterator does NOT support the
* remove method.
*
* @return an iterator over the elements in this list in proper sequence
*/
public Iterator iterator() {
return new COWIterator(getArray(), 0);
}
/**
* {@inheritDoc}
*
* <p>The returned iterator provides a snapshot of the state of the list
* when the iterator was constructed. No synchronization is needed while
* traversing the iterator. The iterator does NOT support the
* remove, set or add methods.
*/
public ListIterator listIterator() {
return new COWIterator(getArray(), 0);
}
/**
* {@inheritDoc}
*
* <p>The list iterator returned by this implementation will throw an
* UnsupportedOperationException in its remove,
* set and add methods.
*
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public ListIterator listIterator(final int index) {
Object[] elements = getArray();
int len = elements.length;
if (index < 0 || index > len)
throw new IndexOutOfBoundsException("Index: " + index);
return new COWIterator(getArray(), index);
}
private static class COWIterator implements ListIterator {
/** Snapshot of the array **/
private final Object[] snapshot;
/** Index of element to be returned by subsequent call to next. */
private int cursor;
private COWIterator(Object[] elements, int initialCursor) {
cursor = initialCursor;
snapshot = elements;
}
public boolean hasNext() {
return cursor < snapshot.length;
}
public boolean hasPrevious() {
return cursor > 0;
}
public Object next() {
try {
return (snapshot[cursor++]);
} catch (IndexOutOfBoundsException ex) {
throw new NoSuchElementException();
}
}
public Object previous() {
try {
return (snapshot[--cursor]);
} catch (IndexOutOfBoundsException e) {
throw new NoSuchElementException();
}
}
public int nextIndex() {
return cursor;
}
public int previousIndex() {
return cursor - 1;
}
/**
* Not supported. Always throws UnsupportedOperationException.
* @throws UnsupportedOperationException always; remove
* is not supported by this iterator.
*/
public void remove() {
throw new UnsupportedOperationException();
}
/**
* Not supported. Always throws UnsupportedOperationException.
* @throws UnsupportedOperationException always; set
* is not supported by this iterator.
*/
public void set(Object e) {
throw new UnsupportedOperationException();
}
/**
* Not supported. Always throws UnsupportedOperationException.
* @throws UnsupportedOperationException always; add
* is not supported by this iterator.
*/
public void add(Object e) {
throw new UnsupportedOperationException();
}
}
/**
* Returns a view of the portion of this list between
* fromIndex, inclusive, and toIndex, exclusive.
* The returned list is backed by this list, so changes in the
* returned list are reflected in this list, and vice-versa.
* While mutative operations are supported, they are probably not
* very useful for CopyOnWriteArrayLists.
*
* <p>The semantics of the list returned by this method become
* undefined if the backing list (i.e., this list) is
* structurally modified in any way other than via the
* returned list. (Structural modifications are those that change
* the size of the list, or otherwise perturb it in such a fashion
* that iterations in progress may yield incorrect results.)
*
* @param fromIndex low endpoint (inclusive) of the subList
* @param toIndex high endpoint (exclusive) of the subList
* @return a view of the specified range within this list
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public synchronized List subList(int fromIndex, int toIndex) {
Object[] elements = getArray();
int len = elements.length;
if (fromIndex < 0 || toIndex > len || fromIndex > toIndex)
throw new IndexOutOfBoundsException();
return new COWSubList(this, fromIndex, toIndex);
}
/**
* Sublist for CopyOnWriteArrayList.
* This class extends AbstractList merely for convenience, to
* avoid having to define addAll, etc. This doesn"t hurt, but
* is wasteful. This class does not need or use modCount
* mechanics in AbstractList, but does need to check for
* concurrent modification using similar mechanics. On each
* operation, the array that we expect the backing list to use
* is checked and updated. Since we do this for all of the
* base operations invoked by those defined in AbstractList,
* all is well. While inefficient, this is not worth
* improving. The kinds of list operations inherited from
* AbstractList are already so slow on COW sublists that
* adding a bit more space/time doesn"t seem even noticeable.
*/
private static class COWSubList extends AbstractList {
private final CopyOnWriteArrayList l;
private final int offset;
private int size;
private Object[] expectedArray;
// only call this holding l"s lock
private COWSubList(CopyOnWriteArrayList list,
int fromIndex, int toIndex) {
l = list;
expectedArray = l.getArray();
offset = fromIndex;
size = toIndex - fromIndex;
}
// only call this holding l"s lock
private void checkForComodification() {
if (l.getArray() != expectedArray)
throw new ConcurrentModificationException();
}
// only call this holding l"s lock
private void rangeCheck(int index) {
if (index < 0 || index >= size)
throw new IndexOutOfBoundsException("Index: " + index +
",Size: " + size);
}
public Object set(int index, Object element) {
synchronized (l) {
rangeCheck(index);
checkForComodification();
Object x = l.set(index + offset, element);
expectedArray = l.getArray();
return x;
}
}
public Object get(int index) {
synchronized (l) {
rangeCheck(index);
checkForComodification();
return l.get(index + offset);
}
}
public int size() {
synchronized (l) {
checkForComodification();
return size;
}
}
public void add(int index, Object element) {
synchronized (l) {
checkForComodification();
if (index<0 || index>size)
throw new IndexOutOfBoundsException();
l.add(index + offset, element);
expectedArray = l.getArray();
size++;
}
}
public void clear() {
synchronized (l) {
checkForComodification();
l.removeRange(offset, offset+size);
expectedArray = l.getArray();
size = 0;
}
}
public Object remove(int index) {
synchronized (l) {
rangeCheck(index);
checkForComodification();
Object result = l.remove(index + offset);
expectedArray = l.getArray();
size--;
return result;
}
}
public Iterator iterator() {
synchronized (l) {
checkForComodification();
return new COWSubListIterator(l, 0, offset, size);
}
}
public ListIterator listIterator(final int index) {
synchronized (l) {
checkForComodification();
if (index<0 || index>size)
throw new IndexOutOfBoundsException("Index: "+index+
", Size: "+size);
return new COWSubListIterator(l, index, offset, size);
}
}
public List subList(int fromIndex, int toIndex) {
synchronized (l) {
checkForComodification();
if (fromIndex<0 || toIndex>size)
throw new IndexOutOfBoundsException();
return new COWSubList(l, fromIndex + offset,
toIndex + offset);
}
}
}
private static class COWSubListIterator implements ListIterator {
private final ListIterator i;
private final int offset;
private final int size;
private COWSubListIterator(List l, int index, int offset,
int size) {
this.offset = offset;
this.size = size;
i = l.listIterator(index + offset);
}
public boolean hasNext() {
return nextIndex() < size;
}
public Object next() {
if (hasNext())
return i.next();
else
throw new NoSuchElementException();
}
public boolean hasPrevious() {
return previousIndex() >= 0;
}
public Object previous() {
if (hasPrevious())
return i.previous();
else
throw new NoSuchElementException();
}
public int nextIndex() {
return i.nextIndex() - offset;
}
public int previousIndex() {
return i.previousIndex() - offset;
}
public void remove() {
throw new UnsupportedOperationException();
}
public void set(Object e) {
throw new UnsupportedOperationException();
}
public void add(Object e) {
throw new UnsupportedOperationException();
}
}
// // Support for resetting lock while deserializing // private static final Unsafe unsafe = Unsafe.getUnsafe(); // private static final long lockOffset; // static { // try { // lockOffset = unsafe.objectFieldOffset // (CopyOnWriteArrayList.class.getDeclaredField("lock")); // } catch (Exception ex) { throw new Error(ex); } // } // private void resetLock() { // unsafe.putObjectVolatile(this, lockOffset, new ReentrantLock()); // } //
// Temporary emulations of anticipated new j.u.Arrays functions
private static Object[] copyOfRange(Object[] original, int from, int to,
Class newType) {
int newLength = to - from;
if (newLength < 0)
throw new IllegalArgumentException(from + " > " + to);
Object[] copy = (Object[]) java.lang.reflect.Array.newInstance
(newType.getComponentType(), newLength);
System.arraycopy(original, from, copy, 0,
Math.min(original.length - from, newLength));
return copy;
}
private static Object[] copyOf(Object[] original, int newLength,
Class newType) {
Object[] copy = (Object[]) java.lang.reflect.Array.newInstance
(newType.getComponentType(), newLength);
System.arraycopy(original, 0, copy, 0,
Math.min(original.length, newLength));
return copy;
}
private static Object[] copyOf(Object[] original, int newLength) {
return copyOf(original, newLength, original.getClass());
}
}
</source>
Find maximum element of Java ArrayList
<source lang="java">
import java.util.ArrayList; import java.util.Collections; public class Main {
public static void main(String[] args) {
ArrayList<Integer> arrayList = new ArrayList<Integer>();
arrayList.add(new Integer("3"));
arrayList.add(new Integer("1"));
arrayList.add(new Integer("8"));
arrayList.add(new Integer("3"));
arrayList.add(new Integer("5"));
Object obj = Collections.max(arrayList);
System.out.println(obj);
}
} //8
</source>
Find Minimum element of Java ArrayList
<source lang="java">
import java.util.ArrayList; import java.util.Collections; public class Main {
public static void main(String[] args) {
ArrayList<Integer> arrayList = new ArrayList<Integer>();
arrayList.add(new Integer("1"));
arrayList.add(new Integer("2"));
arrayList.add(new Integer("3"));
arrayList.add(new Integer("4"));
arrayList.add(new Integer("5"));
Object obj = Collections.min(arrayList);
System.out.println(obj);
}
}
</source>
Get element in an ArrayList by index
<source lang="java">
import java.util.ArrayList; public class Main {
public static void main(String[] args) {
ArrayList<String> arrayList = new ArrayList<String>();
arrayList.add("1");
arrayList.add("2");
arrayList.add("3");
System.out.println(arrayList.get(0));
System.out.println(arrayList.get(1));
System.out.println(arrayList.get(2));
}
}
</source>
Get Enumeration over Java ArrayList
<source lang="java">
import java.util.ArrayList; import java.util.Collections; import java.util.Enumeration; public class Main {
public static void main(String[] args) {
ArrayList<String> arrayList = new ArrayList<String>();
arrayList.add("A");
arrayList.add("B");
arrayList.add("D");
arrayList.add("E");
arrayList.add("F");
Enumeration e = Collections.enumeration(arrayList);
while (e.hasMoreElements())
System.out.println(e.nextElement());
}
}
</source>
Get generic Iterator from generic ArrayList
<source lang="java">
/*
* Copyright (c) 1995 - 2008 Sun Microsystems, Inc. All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * * - Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * * - Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * - Neither the name of Sun Microsystems nor the names of its * contributors may be used to endorse or promote products derived * from this software without specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */
import java.text.DateFormatSymbols; import java.util.ArrayList; import java.util.Arrays; import java.util.Collection; import java.util.Iterator; public class OysterMonths {
Collection<String> safeMonths;
public Collection<String> filter(Collection<String> c) {
Collection<String> filteredCollection = new ArrayList<String>();
for (Iterator<String> i = c.iterator(); i.hasNext();) {
String s = i.next();
if (condition(s)) {
filteredCollection.add(s);
}
}
return filteredCollection;
}
public boolean condition(String s) {
return s.contains("r");
}
public static void main(String[] args) {
OysterMonths om = new OysterMonths();
DateFormatSymbols dfs = new DateFormatSymbols();
String[] monthArray = dfs.getMonths();
Collection<String> months = Arrays.asList(monthArray);
om.safeMonths = om.filter(months);
System.out.println("The following months are safe for oysters:");
System.out.println(om.safeMonths);
}
}
</source>
Get Previous and next index using Java ListIterator
<source lang="java">
import java.util.ArrayList; import java.util.ListIterator; public class Main {
public static void main(String[] args) {
ArrayList<String> aList = new ArrayList<String>();
aList.add("1");
aList.add("2");
aList.add("3");
aList.add("4");
aList.add("5");
ListIterator<String> listIterator = aList.listIterator();
System.out.println("Previous: " + listIterator.previousIndex());
System.out.println("Next: " + listIterator.nextIndex());
// advance current position by one using next method
listIterator.next();
System.out.println("Previous: " + listIterator.previousIndex());
System.out.println("Next: " + listIterator.nextIndex());
}
}
</source>
Get Size of Java ArrayList and loop through elements
<source lang="java">
import java.util.ArrayList; public class Main {
public static void main(String[] args) {
ArrayList<String> arrayList = new ArrayList<String>();
arrayList.add("1");
arrayList.add("2");
arrayList.add("3");
int totalElements = arrayList.size();
for (int index = 0; index < totalElements; index++)
System.out.println(arrayList.get(index));
}
}
</source>
Get Sub List of Java ArrayList
<source lang="java">
import java.util.ArrayList; import java.util.List; public class Main {
public static void main(String[] args) {
ArrayList<String> arrayList = new ArrayList<String>();
arrayList.add("1");
arrayList.add("2");
arrayList.add("3");
arrayList.add("4");
arrayList.add("5");
List lst = arrayList.subList(1, 3);
for (int i = 0; i < lst.size(); i++)
System.out.println(lst.get(i));
// remove one element from sub list
Object obj = lst.remove(0);
System.out.println(obj + " is removed");
for (String str: arrayList)
System.out.println(str);
}
}
</source>
Get Synchronized List from Java ArrayList
<source lang="java">
import java.util.ArrayList; import java.util.Collections; import java.util.List; public class Main {
public static void main(String[] args) {
ArrayList arrayList = new ArrayList();
List list = Collections.synchronizedList(arrayList);
}
}
</source>
Get the size of an arraylist after and before add and remove methods
<source lang="java">
import java.util.ArrayList; class ArrayListDemo {
public static void main(String args[]) {
ArrayList<String> al = new ArrayList<String>();
System.out.println("Initial size of al: " + al.size());
al.add("C");
al.add("A");
al.add("E");
al.add("B");
al.add("D");
al.add("F");
al.add(1, "A2");
System.out.println("Size of al after additions: " + al.size());
System.out.println("Contents of al: " + al);
al.remove("F");
al.remove(2);
System.out.println("Size of al after deletions: " + al.size());
System.out.println("Contents of al: " + al);
}
}
</source>
How to Convert an ArrayList into an array
<source lang="java">
import java.util.ArrayList; public class Main {
public static void main(String[] args) {
ArrayList<Integer> al = new ArrayList<Integer>();
al.add(new Integer(1));
al.add(new Integer(2));
al.add(new Integer(3));
al.add(new Integer(4));
al.add(new Integer(5));
System.out.println("contents of al : " + al);
Object ia[] = al.toArray(); // get array
int sum = 0;
for (int i = 0; i < ia.length; i++){
sum += ((Integer) ia[i]).intValue();
}
System.out.println("Sum is :" + sum);
}
}
</source>
If an ArrayList contains a given item
<source lang="java">
import java.util.ArrayList; import java.util.List; public class Main {
public static void main(String[] args) {
List list = new ArrayList();
list.add("Item 1");
list.add("Item 2");
if (list.contains("Item 1")) {
System.out.println("True");
} else {
System.out.println("False");
}
}
}
</source>
Insert all elements of other Collection to Specified Index of Java ArrayList
<source lang="java">
import java.util.ArrayList; import java.util.Vector; public class Main {
public static void main(String[] args) {
ArrayList<String> arrayList = new ArrayList<String>();
arrayList.add("1");
arrayList.add("2");
arrayList.add("3");
Vector<String> v = new Vector<String>();
v.add("4");
v.add("5");
// insert all elements of Vector to ArrayList at index 1
arrayList.addAll(1, v);
for (String str: arrayList)
System.out.println(str);
}
} /* 1 4 5 2 3
- /
</source>
Iterate through a Collection using Java Iterator
<source lang="java">
import java.util.ArrayList; import java.util.Iterator; public class Main {
public static void main(String[] args) {
ArrayList<String> aList = new ArrayList<String>();
aList.add("1");
aList.add("2");
aList.add("3");
aList.add("4");
aList.add("5");
Iterator itr = aList.iterator();
// iterate through the ArrayList values using Iterator"s hasNext and next methods
while (itr.hasNext()){
System.out.println(itr.next());
}
}
}
</source>
Iterate through elements Java ArrayList using Iterator
<source lang="java">
import java.util.ArrayList; import java.util.Iterator; public class Main {
public static void main(String[] args) {
ArrayList<String> arrayList = new ArrayList<String>();
arrayList.add("1");
arrayList.add("2");
arrayList.add("3");
arrayList.add("4");
arrayList.add("5");
Iterator itr = arrayList.iterator();
while (itr.hasNext()){
System.out.println(itr.next());
}
}
}
</source>
Iterate through elements Java ArrayList using ListIterator
<source lang="java">
import java.util.ArrayList; import java.util.ListIterator; public class Main {
public static void main(String[] args) {
ArrayList<String> arrayList = new ArrayList<String>();
arrayList.add("1");
arrayList.add("2");
arrayList.add("3");
arrayList.add("4");
arrayList.add("5");
ListIterator itr = arrayList.listIterator();
System.out.println("in forward direction");
while (itr.hasNext()) {
System.out.println(itr.next());
}
System.out.println("in backward direction");
while (itr.hasPrevious()) {
System.out.println(itr.previous());
}
}
} /*in forward direction 1 2 3 4 5 in backward direction 5 4 3 2 1
- /
</source>
Looping through a Collection object: while loop, iterator, and for each
<source lang="java">
import java.util.ArrayList; import java.util.Iterator; public class Main {
public static void main(String[] args) {
ArrayList<String> list = new ArrayList<String>();
list.add("Monday");
list.add("Tuesdag");
list.add("Wednesday");
list.add("Thursday");
list.add("Friday");
list.add("Saturday");
list.add("Sunday");
Iterator<String> iterator = null;
iterator = list.iterator();
while (iterator.hasNext()) {
String element = iterator.next();
System.out.println(element);
}
for (iterator = list.iterator(); iterator.hasNext();) {
String element = iterator.next();
System.out.println(element);
}
for (String element : list) {
System.out.println(element);
}
}
} /* Monday Tuesdag Wednesday Thursday Friday Saturday Sunday Monday Tuesdag Wednesday Thursday Friday Saturday Sunday Monday Tuesdag Wednesday Thursday Friday Saturday Sunday
- /
</source>
pass the actual object you want removed.
<source lang="java">
import java.util.ArrayList; public class MainClass {
public static void main(String[] a) {
ArrayList<Employee> emps = new ArrayList<Employee>();
Employee emp1 = new Employee("A", "G");
Employee emp2 = new Employee("T", "A");
Employee emp3 = new Employee("K", "J");
emps.add(emp1);
emps.add(emp2);
emps.add(emp3);
System.out.println(emps);
emps.remove(emp2);
System.out.println(emps);
}
} class Address { } class Employee {
private String lastName;
private String firstName;
private Double salary;
public Address address;
public Employee(String lastName, String firstName) {
this.lastName = lastName;
this.firstName = firstName;
this.address = new Address();
}
public String getLastName() {
return this.lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
public String getFirstName() {
return this.firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public double getSalary() {
return this.salary;
}
public void setSalary(double salary) {
this.salary = salary;
}
}
</source>
Perform Binary Search on Java ArrayList
<source lang="java">
import java.util.ArrayList; import java.util.Collections; public class Main {
public static void main(String[] args) {
ArrayList<String> arrayList = new ArrayList<String>();
arrayList.add("1");
arrayList.add("4");
arrayList.add("2");
arrayList.add("5");
arrayList.add("3");
Collections.sort(arrayList);
System.out.println("Sorted ArrayList contains : " + arrayList);
int index = Collections.binarySearch(arrayList, "4");
System.out.println("Element found at : " + index);
}
}
</source>
Pre-generics example that uses a collection.
<source lang="java">
import java.util.ArrayList; import java.util.Iterator; class OldStyle {
public static void main(String args[]) {
ArrayList list = new ArrayList();
list.add("one");
list.add("two");
list.add("three");
list.add("four");
Iterator itr = list.iterator();
while (itr.hasNext()) {
String str = (String) itr.next(); // explicit cast needed here.
System.out.println(str + " is " + str.length() + " chars long.");
}
}
}
</source>
Remove all elements from Java ArrayList
<source lang="java">
import java.util.ArrayList; public class Main {
public static void main(String[] args) {
ArrayList<String> arrayList = new ArrayList<String>();
arrayList.add("1");
arrayList.add("2");
arrayList.add("3");
System.out.println(arrayList.size());
arrayList.clear();
System.out.println(arrayList.size());
}
}
</source>
Remove an element from ArrayList using Java ListIterator
<source lang="java">
import java.util.ArrayList; import java.util.ListIterator; public class Main {
public static void main(String[] args) {
ArrayList<String> aList = new ArrayList<String>();
aList.add("1");
aList.add("2");
aList.add("3");
aList.add("4");
aList.add("5");
// Get an object of ListIterator using listIterator() method
ListIterator listIterator = aList.listIterator();
listIterator.next();
listIterator.next();
// remove element returned by last next method
listIterator.remove();
for (String str: aList){
System.out.println(str);
}
}
}
</source>
Remove an element from Collection using Java Iterator
<source lang="java">
import java.util.ArrayList; import java.util.Iterator; public class Main {
public static void main(String[] args) {
ArrayList<String> aList = new ArrayList<String>();
aList.add("1");
aList.add("2");
aList.add("3");
aList.add("4");
aList.add("5");
for (String str: aList) {
System.out.println(str);
}
Iterator itr = aList.iterator();
// remove 2 from ArrayList using Iterator"s remove method.
String strElement = "";
while (itr.hasNext()) {
strElement = (String) itr.next();
if (strElement.equals("2")) {
itr.remove();
break;
}
}
for (String str: aList) {
System.out.println(str);
}
}
}
</source>
Remove an element from specified index of Java ArrayList
<source lang="java">
import java.util.ArrayList; public class Main {
public static void main(String[] args) {
ArrayList<String> arrayList = new ArrayList<String>();
arrayList.add("1");
arrayList.add("2");
arrayList.add("3");
Object obj = arrayList.remove(1);
System.out.println(obj + " is removed from ArrayList");
for (String str: arrayList)
System.out.println(str);
}
}
</source>
Remove duplicate items from an ArrayList
<source lang="java">
import java.util.ArrayList; import java.util.HashSet; import java.util.List; public class Main {
public static void main(String[] argv) {
List<String> arrayList1 = new ArrayList<String>();
arrayList1.add("A");
arrayList1.add("A");
arrayList1.add("B");
arrayList1.add("B");
arrayList1.add("B");
arrayList1.add("C");
HashSet<String> hashSet = new HashSet<String>(arrayList1);
List<String> arrayList2 = new ArrayList<String>(hashSet);
for (Object item : arrayList2)
System.out.println(item);
}
} /* A B C
- /
</source>
Replace All Elements Of Java ArrayList
<source lang="java">
import java.util.ArrayList; import java.util.Collections; public class Main {
public static void main(String[] args) {
ArrayList<String> arrayList = new ArrayList<String>();
arrayList.add("A");
arrayList.add("B");
arrayList.add("D");
System.out.println(arrayList);
Collections.fill(arrayList, "REPLACED");
System.out.println(arrayList);
}
} /* [A, B, D] [REPLACED, REPLACED, REPLACED]
- /
</source>
Replace all occurrences of specified element of Java ArrayList
<source lang="java">
import java.util.ArrayList; import java.util.Collections; public class Main {
public static void main(String[] args) {
ArrayList<String> arrayList = new ArrayList<String>();
arrayList.add("A");
arrayList.add("B");
arrayList.add("A");
arrayList.add("C");
arrayList.add("D");
System.out.println(arrayList);
Collections.replaceAll(arrayList, "A", "Replace All");
System.out.println(arrayList);
}
} /* [A, B, A, C, D] [Replace All, B, Replace All, C, D]
- /
</source>
Replace an element at specified index of Java ArrayList
<source lang="java">
import java.util.ArrayList; public class Main {
public static void main(String[] args) {
ArrayList<String> arrayList = new ArrayList<String>();
arrayList.add("1");
arrayList.add("2");
arrayList.add("3");
arrayList.set(1, "REPLACED ELEMENT");
for (String str: arrayList){
System.out.println(str);
}
}
} /* 1 REPLACED ELEMENT 3
- /
</source>
Replace an element from ArrayList using Java ListIterator
<source lang="java">
import java.util.ArrayList; import java.util.ListIterator; public class Main {
public static void main(String[] args) {
ArrayList<String> aList = new ArrayList<String>();
aList.add("1");
aList.add("2");
aList.add("3");
aList.add("4");
aList.add("5");
ListIterator<String> listIterator = aList.listIterator();
listIterator.next();
listIterator.set("100");
for (String str : aList) {
System.out.println(str);
}
}
}
</source>
Reverse order of all elements of Java ArrayList
<source lang="java">
import java.util.ArrayList; import java.util.Collections; public class Main {
public static void main(String[] args) {
ArrayList<String> arrayList = new ArrayList<String>();
arrayList.add("A");
arrayList.add("B");
arrayList.add("C");
arrayList.add("D");
arrayList.add("E");
System.out.println(arrayList);
Collections.reverse(arrayList);
System.out.println(arrayList);
}
}
</source>
Rotate elements of a collection
<source lang="java">
import java.util.ArrayList; import java.util.Arrays; import java.util.Collections; import java.util.List; public class Main {
public static void main(String[] args) {
List numbers = new ArrayList();
for (int i = 0; i < 25; i++) {
numbers.add(i);
}
System.out.println(Arrays.toString(numbers.toArray()));
Collections.rotate(numbers, 10);
System.out.println(Arrays.toString(numbers.toArray()));
}
}
</source>
Search an element of Java ArrayList
<source lang="java">
import java.util.ArrayList; public class Main {
public static void main(String[] args) {
ArrayList<String> arrayList = new ArrayList<String>();
arrayList.add("2");
arrayList.add("2");
arrayList.add("3");
arrayList.add("4");
arrayList.add("5");
arrayList.add("1");
arrayList.add("2");
System.out.println(arrayList.contains("2"));
int index = arrayList.indexOf("4");
if (index == -1)
System.out.println("not contain 4");
else
System.out.println("4 at index :" + index);
int lastIndex = arrayList.lastIndexOf("1");
if (lastIndex == -1)
System.out.println("not contain 1");
else
System.out.println("Last index :"+ lastIndex);
}
} /*true 4 at index :3 Last index :5
- /
</source>
Search collection element
<source lang="java">
import java.text.DateFormatSymbols; import java.util.Collections; import java.util.LinkedList; import java.util.List; public class Main {
public static void main(String[] args) {
List list = new LinkedList();
DateFormatSymbols dfs = new DateFormatSymbols();
String[] months = dfs.getMonths();
for (int i = 0; i < months.length; i++) {
String month = months[i];
list.add(month);
}
Collections.sort(list);
System.out.println("Month Names = " + list);
int index = Collections.binarySearch(list, "October");
if (index > 0) {
System.out.println("Found at index = " + index);
String month = (String) list.get(index);
System.out.println("Month = " + month);
}
}
}
</source>
shows the modern, generic form of collection classes
<source lang="java">
import java.util.ArrayList; import java.util.Iterator; class NewStyle {
public static void main(String args[]) {
ArrayList<String> list = new ArrayList<String>();
list.add("one");
list.add("two");
list.add("three");
list.add("four");
Iterator<String> itr = list.iterator();
while (itr.hasNext()) {
String str = itr.next(); // no cast needed
System.out.println(str + " is " + str.length() + " chars long.");
}
}
}
</source>
Shuffle elements of Java ArrayList
<source lang="java">
import java.util.ArrayList; import java.util.Collections; public class Main {
public static void main(String[] args) {
ArrayList<String> arrayList = new ArrayList<String>();
arrayList.add("A");
arrayList.add("B");
arrayList.add("C");
arrayList.add("D");
arrayList.add("E");
System.out.println(arrayList);
Collections.shuffle(arrayList);
System.out.println(arrayList);
}
} /* [A, B, C, D, E] [E, D, A, C, B]
- /
</source>
Sort elements of Java ArrayList
<source lang="java">
import java.util.ArrayList; import java.util.Collections; public class Main {
public static void main(String[] args) {
ArrayList<String> arrayList = new ArrayList<String>();
arrayList.add("1");
arrayList.add("3");
arrayList.add("5");
arrayList.add("2");
arrayList.add("4");
Collections.sort(arrayList);
for (String str: arrayList)
System.out.println(str);
}
} /* 1 2 3 4 5
- /
</source>
Sort items of an ArrayList
<source lang="java">
import java.util.ArrayList; import java.util.Arrays; import java.util.Collections; import java.util.List; public class Main {
public static void main(String[] args) {
List<String> colours = new ArrayList<String>();
colours.add("red");
colours.add("green");
colours.add("blue");
colours.add("yellow");
colours.add("cyan");
colours.add("white");
colours.add("black");
Collections.sort(colours);
System.out.println(Arrays.toString(colours.toArray()));
Collections.sort(colours, Collections.reverseOrder());
System.out.println(Arrays.toString(colours.toArray()));
}
}
</source>
Sort Java ArrayList in descending order using comparator
<source lang="java">
import java.util.ArrayList; import java.util.Collections; import java.util.ruparator; public class Main {
public static void main(String[] args) {
ArrayList<String> arrayList = new ArrayList<String>();
arrayList.add("A");
arrayList.add("B");
arrayList.add("C");
arrayList.add("D");
arrayList.add("E");
Comparator comparator = Collections.reverseOrder();
System.out.println(arrayList);
Collections.sort(arrayList, comparator);
System.out.println(arrayList);
}
}
</source>
Store user-defined objects in arraylist
<source lang="java">
import java.util.ArrayList; public class MainClass {
public static void main(String[] a) {
ArrayList<Employee> emps = new ArrayList<Employee>();
emps.add(new Employee("A", "G"));
emps.add(new Employee("T", "A"));
emps.add(new Employee("K", "J"));
System.out.println(emps);
Employee e = emps.get(1);
e.setLastName("new");
System.out.println(emps);
}
} class Address { } class Employee {
private String lastName;
private String firstName;
private Double salary;
public Address address;
public Employee(String lastName, String firstName) {
this.lastName = lastName;
this.firstName = firstName;
this.address = new Address();
}
public String getLastName() {
return this.lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
public String getFirstName() {
return this.firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public double getSalary() {
return this.salary;
}
public void setSalary(double salary) {
this.salary = salary;
}
}
</source>
Swap elements of Java ArrayList
<source lang="java">
import java.util.ArrayList; import java.util.Collections; public class Main {
public static void main(String[] args) {
ArrayList<String> arrayList = new ArrayList<String>();
arrayList.add("A");
arrayList.add("B");
arrayList.add("C");
arrayList.add("D");
arrayList.add("E");
System.out.println(arrayList);
Collections.swap(arrayList, 0, 4);
System.out.println(arrayList);
}
} /* [A, B, C, D, E] [E, B, C, D, A]
- /
</source>
Traverse through ArrayList in forward direction using Java ListIterator
<source lang="java">
import java.util.ArrayList; import java.util.ListIterator; public class Main {
public static void main(String[] args) {
ArrayList<String> aList = new ArrayList<String>();
aList.add("1");
aList.add("2");
aList.add("3");
aList.add("4");
aList.add("5");
ListIterator listIterator = aList.listIterator();
while (listIterator.hasNext()){
System.out.println(listIterator.next());
}
}
}
</source>
Traverse through ArrayList in reverse direction using Java ListIterator
<source lang="java">
import java.util.ArrayList; import java.util.ListIterator; public class Main {
public static void main(String[] args) {
ArrayList<String> aList = new ArrayList<String>();
aList.add("1");
aList.add("2");
aList.add("3");
aList.add("4");
aList.add("5");
ListIterator<String> listIterator = aList.listIterator();
while (listIterator.hasNext()){
System.out.println(listIterator.next());
}
while (listIterator.hasPrevious()){
System.out.println(listIterator.previous());
}
}
}
</source>
Use set method to change the value in an array list
<source lang="java">
import java.util.ArrayList; public class MainClass {
public static void main(String[] a) {
ArrayList<String> nums = new ArrayList<String>();
nums.clear();
nums.add("One");
nums.add("Two");
nums.add("Three");
System.out.println(nums);
nums.set(0, "Uno");
nums.set(1, "Dos");
nums.set(2, "Tres");
System.out.println(nums);
}
}
</source>
Use the Iterator returned from ArrayList to loop through an array list
<source lang="java">
import java.util.ArrayList; import java.util.Iterator; public class MainClass {
public static void main(String[] a) {
ArrayList<String> nums = new ArrayList<String>();
nums.add("O");
nums.add("Two");
nums.add("Three");
nums.add("Four");
String s;
Iterator e = nums.iterator();
while (e.hasNext()) {
s = (String) e.next();
System.out.println(s);
}
}
}
</source>
