Java Tutorial/Collections/Collections Search

A binary search implementation.

   <source lang="java">

/*

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// ---------------------------------------------------------------------------- /**

* A binary search implementation.
*/

public class BinarySearch {

 public int find(final int[] data, final int key) {
   int low = 0, high = data.length - 1;
   while (low <= high) {
     final int i = (low + high) >> 1;
     final int v = data[i];
     if (v == key)
       return i; // this line does not get covered unless there is a match
     else if (v < key)
       low = i + 1;
     else
       // v > key
       high = i - 1;
   }
   return -1;
 }

}</source>

Binary Searching

   <source lang="java">

import java.util.ArrayList; import java.util.Arrays; import java.util.Collections; import java.util.List; public class MainClass {

 public static void main(String args[]) {
   String str[] = { "B", "H", "L", "M", "I", "N", "R" };
   // Convert to list
   List list = new ArrayList(Arrays.asList(str));
   // Ensure list sorted
   Collections.sort(list);
   System.out.println("Sorted list: [length: " + list.size() + "]");
   System.out.println(list);
   // Search for element in list
   int index = Collections.binarySearch(list, "M");
   System.out.println("Found M @ " + index);
   // Search for element not in list
   index = Collections.binarySearch(list, "J");
   System.out.println("Didn"t find J @ " + index);
   // Insert
   int newIndex = -index - 1;
   list.add(newIndex, "J");
   System.out.println("With J added: [length: " + list.size() + "]");
   System.out.println(list);
 }

}</source>

Sorted list: [length: 7]
[B, H, I, L, M, N, R]
Found M @ 4
Didn"t find J @ -4
With J added: [length: 8]
[B, H, I, J, L, M, N, R]

Binary search routines

   <source lang="java">

/*

* Copyright (c) 1998-2002 Carnegie Mellon University.  All rights
* reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
*    notice, this list of conditions and the following disclaimer.
*
* 2. 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.
*
* THIS SOFTWARE IS PROVIDED BY CARNEGIE MELLON UNIVERSITY ``AS IS"" AND
* ANY EXPRESSED 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 CARNEGIE MELLON UNIVERSITY
* NOR ITS EMPLOYEES 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.
*
*/

/**

* Binary search routines.
*/

public abstract class BinarySearch {

   /**
    * Search a sorted array of integers.
    * @param array Array of integers
    * @param offset Starting offset of subarray to search
    * @param length Length of subarray to search
    * @param x Value to search for
    * @return largest index i in subarray (offset <= i <= offset+length)
    * such that all elements below i in the subarray are strictly less
    * than x.  If x is found in the subarray, then array[i] == x (and i is
    * the first occurence of x in the subarray).  If x is not found, 
    * then array[i] is where x should be inserted in the sort order.
    */
   public static int search (int[] array, int offset, int length, int x) {
       // handle 0-length subarray case right away
       if (length <= 0)
           return offset;
       int low = offset;
       int high = offset+length-1;
       // since length > 0, array[low] and array[high] are valid indices
       if (x <= array[low])
           return low;
       if (x > array[high])
           return high+1;
       
       while (low+1 < high) {
           // loop invariant: array[low] < x <= array[high],
           //                 offset <= low < high < offset+length
           int mid = (low + high)/2;
           if (x <= array[mid])
               high = mid;
           else
               low = mid;
       }
       // now we have array[low] < x <= array[high]
       //             && (low+1 == high || low == high)
       //  implies low+1 == high
       //debug.assertion (low+1 == high);
       return high;
   }

}</source>

Check whether the given Collection contains the given element instance.

   <source lang="java">

import java.util.Arrays; import java.util.Collection; import java.util.Enumeration; import java.util.Iterator; import java.util.List; import java.util.Map; import java.util.Properties; /*

* Copyright 2002-2007 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*      http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

/**

* Miscellaneous collection utility methods.
* Mainly for internal use within the framework.
*
* @author Juergen Hoeller
* @author Rob Harrop
* @since 1.1.3
*/

abstract class CollectionUtils {

 /**
  * Check whether the given Collection contains the given element instance.
  * Enforces the given instance to be present, rather than returning
  * true for an equal element as well.
  * @param collection the Collection to check
  * @param element the element to look for
  * @return true if found, false else
  */
 public static boolean containsInstance(Collection collection, Object element) {
   if (collection != null) {
     for (Iterator it = collection.iterator(); it.hasNext();) {
       Object candidate = it.next();
       if (candidate == element) {
         return true;
       }
     }
   }
   return false;
 }
 /**
  * Return true if the supplied Collection is null
  * or empty. Otherwise, return false.
  * @param collection the Collection to check
  * @return whether the given Collection is empty
  */
 public static boolean isEmpty(Collection collection) {
   return (collection == null || collection.isEmpty());
 }
 /**
  * Return true if the supplied Map is null
  * or empty. Otherwise, return false.
  * @param map the Map to check
  * @return whether the given Map is empty
  */
 public static boolean isEmpty(Map map) {
   return (map == null || map.isEmpty());
 }

 /**
  * Return true if any element in "candidates" is
  * contained in "source"; otherwise returns false.
  * @param source the source Collection
  * @param candidates the candidates to search for
  * @return whether any of the candidates has been found
  */
 public static boolean containsAny(Collection source, Collection candidates) {
   if (isEmpty(source) || isEmpty(candidates)) {
     return false;
   }
   for (Iterator it = candidates.iterator(); it.hasNext();) {
     if (source.contains(it.next())) {
       return true;
     }
   }
   return false;
 }
 /**
  * Return the first element in "candidates" that is contained in
  * "source". If no element in "candidates" is present in
  * "source" returns null. Iteration order is
  * {@link Collection} implementation specific.
  * @param source the source Collection
  * @param candidates the candidates to search for
  * @return the first present object, or null if not found
  */
 public static Object findFirstMatch(Collection source, Collection candidates) {
   if (isEmpty(source) || isEmpty(candidates)) {
     return null;
   }
   for (Iterator it = candidates.iterator(); it.hasNext();) {
     Object candidate = it.next();
     if (source.contains(candidate)) {
       return candidate;
     }
   }
   return null;
 }
 /**
  * Find a value of the given type in the given Collection.
  * @param collection the Collection to search
  * @param type the type to look for
  * @return a value of the given type found, or null if none
  * @throws IllegalArgumentException if more than one value of the given type found
  */
 public static Object findValueOfType(Collection collection, Class type) throws IllegalArgumentException {
   if (isEmpty(collection)) {
     return null;
   }
   Class typeToUse = (type != null ? type : Object.class);
   Object value = null;
   for (Iterator it = collection.iterator(); it.hasNext();) {
     Object obj = it.next();
     if (typeToUse.isInstance(obj)) {
       if (value != null) {
         throw new IllegalArgumentException("More than one value of type [" + typeToUse.getName() + "] found");
       }
       value = obj;
     }
   }
   return value;
 }
 /**
  * Determine whether the given Collection only contains a single unique object.
  * @param collection the Collection to check
  * @return true if the collection contains a single reference or
  * multiple references to the same instance, false else
  */
 public static boolean hasUniqueObject(Collection collection) {
   if (isEmpty(collection)) {
     return false;
   }
   boolean hasCandidate = false;
   Object candidate = null;
   for (Iterator it = collection.iterator(); it.hasNext();) {
     Object elem = it.next();
     if (!hasCandidate) {
       hasCandidate = true;
       candidate = elem;
     }
     else if (candidate != elem) {
       return false;
     }
   }
   return true;
 }

}</source>

Find a value of the given type in the given Collection

   <source lang="java">

import java.util.Arrays; import java.util.Collection; import java.util.Enumeration; import java.util.Iterator; import java.util.List; import java.util.Map; import java.util.Properties; /*

* Copyright 2002-2007 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*      http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

/**

* Miscellaneous collection utility methods.
* Mainly for internal use within the framework.
*
* @author Juergen Hoeller
* @author Rob Harrop
* @since 1.1.3
*/

abstract class CollectionUtils {

 /**
  * Find a value of the given type in the given Collection.
  * @param collection the Collection to search
  * @param type the type to look for
  * @return a value of the given type found, or null if none
  * @throws IllegalArgumentException if more than one value of the given type found
  */
 public static Object findValueOfType(Collection collection, Class type) throws IllegalArgumentException {
   if (isEmpty(collection)) {
     return null;
   }
   Class typeToUse = (type != null ? type : Object.class);
   Object value = null;
   for (Iterator it = collection.iterator(); it.hasNext();) {
     Object obj = it.next();
     if (typeToUse.isInstance(obj)) {
       if (value != null) {
         throw new IllegalArgumentException("More than one value of type [" + typeToUse.getName() + "] found");
       }
       value = obj;
     }
   }
   return value;
 }
 /**
  * Return true if the supplied Collection is null
  * or empty. Otherwise, return false.
  * @param collection the Collection to check
  * @return whether the given Collection is empty
  */
 public static boolean isEmpty(Collection collection) {
   return (collection == null || collection.isEmpty());
 }
 /**
  * Return true if the supplied Map is null
  * or empty. Otherwise, return false.
  * @param map the Map to check
  * @return whether the given Map is empty
  */
 public static boolean isEmpty(Map map) {
   return (map == null || map.isEmpty());
 }

 /**
  * Return the first element in "candidates" that is contained in
  * "source". If no element in "candidates" is present in
  * "source" returns null. Iteration order is
  * {@link Collection} implementation specific.
  * @param source the source Collection
  * @param candidates the candidates to search for
  * @return the first present object, or null if not found
  */
 public static Object findFirstMatch(Collection source, Collection candidates) {
   if (isEmpty(source) || isEmpty(candidates)) {
     return null;
   }
   for (Iterator it = candidates.iterator(); it.hasNext();) {
     Object candidate = it.next();
     if (source.contains(candidate)) {
       return candidate;
     }
   }
   return null;
 }

 /**
  * Determine whether the given Collection only contains a single unique object.
  * @param collection the Collection to check
  * @return true if the collection contains a single reference or
  * multiple references to the same instance, false else
  */
 public static boolean hasUniqueObject(Collection collection) {
   if (isEmpty(collection)) {
     return false;
   }
   boolean hasCandidate = false;
   Object candidate = null;
   for (Iterator it = collection.iterator(); it.hasNext();) {
     Object elem = it.next();
     if (!hasCandidate) {
       hasCandidate = true;
       candidate = elem;
     }
     else if (candidate != elem) {
       return false;
     }
   }
   return true;
 }

}</source>

Get the difference of two collections

   <source lang="java">

import java.util.ArrayList; import java.util.Collection;

public class Utils {

 public static <T> Collection<T> diff(Collection<T> c1, Collection<T> c2) {
   if (c1 == null || c1.size() == 0 || c2 == null || c2.size() == 0) {
       return c1;
   }
   Collection<T> difference = new ArrayList<T>();
   for (T item : c1) {
       if (!c2.contains(item)) {
           difference.add(item);
       }
   }
   return difference;

}

}</source>

Return the first element in "candidates" that is contained in source

   <source lang="java">

import java.util.Arrays; import java.util.Collection; import java.util.Enumeration; import java.util.Iterator; import java.util.List; import java.util.Map; import java.util.Properties; /*

* Copyright 2002-2007 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*      http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

/**

* Miscellaneous collection utility methods.
* Mainly for internal use within the framework.
*
* @author Juergen Hoeller
* @author Rob Harrop
* @since 1.1.3
*/

abstract class CollectionUtils {

 /**
  * Return the first element in "candidates" that is contained in
  * "source". If no element in "candidates" is present in
  * "source" returns null. Iteration order is
  * {@link Collection} implementation specific.
  * @param source the source Collection
  * @param candidates the candidates to search for
  * @return the first present object, or null if not found
  */
 public static Object findFirstMatch(Collection source, Collection candidates) {
   if (isEmpty(source) || isEmpty(candidates)) {
     return null;
   }
   for (Iterator it = candidates.iterator(); it.hasNext();) {
     Object candidate = it.next();
     if (source.contains(candidate)) {
       return candidate;
     }
   }
   return null;
 }
 /**
  * Return true if the supplied Collection is null
  * or empty. Otherwise, return false.
  * @param collection the Collection to check
  * @return whether the given Collection is empty
  */
 public static boolean isEmpty(Collection collection) {
   return (collection == null || collection.isEmpty());
 }
 /**
  * Return true if the supplied Map is null
  * or empty. Otherwise, return false.
  * @param map the Map to check
  * @return whether the given Map is empty
  */
 public static boolean isEmpty(Map map) {
   return (map == null || map.isEmpty());
 }

}</source>