Java Tutorial/Collections/Enumeration Interface — различия между версиями
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Текущая версия на 05:04, 1 июня 2010
Содержание
- 1 An enumeration that iterates over an array.
- 2 Concatenates the content of two enumerations into one.
- 3 Creating Custom Enumerations
- 4 Filters enumeration to contain each of the provided elements just once.
- 5 Filters some elements out from the input enumeration.
- 6 For each element of the input enumeration asks the Processor to provide a replacement
- 7 If you prefer a for-loop
- 8 Removes all nulls from the input enumeration.
- 9 Returns an enumeration that iterates over provided array.
- 10 Serializable Enumeration
- 11 Support for breadth-first enumerating.
- 12 The Enumeration Interface
- 13 The SequenceInputStream Class
- 14 Where do we get the enumeration from?
An enumeration that iterates over an array.
/**
*
* JFreeReport : a free Java reporting library
*
*
* Project Info: http://reporting.pentaho.org/
*
* (C) Copyright 2001-2007, by Object Refinery Ltd, Pentaho Corporation and Contributors.
*
* This library is free software; you can redistribute it and/or modify it under the terms
* of the GNU Lesser General Public License as published by the Free Software Foundation;
* either version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
* without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
* See the GNU Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License along with this
* library; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330,
* Boston, MA 02111-1307, USA.
*
* [Java is a trademark or registered trademark of Sun Microsystems, Inc.
* in the United States and other countries.]
*
* ------------
* ArrayEnumeration.java
* ------------
* (C) Copyright 2001-2007, by Object Refinery Ltd, Pentaho Corporation and Contributors.
*/
import java.util.Enumeration;
import java.util.NoSuchElementException;
/**
* An enumeration that iterates over an array.
*
* @author Thomas Morgner
*/
public class ArrayEnumeration implements Enumeration
{
/** The base datasource. */
private Object[] objectarray = null;
/** The counter holds the current position inside the array. */
private int counter = 0;
/**
* Creates a new enumeration for the given array.
*
* @param objectarray the array over which to iterate
* @throws NullPointerException if the array is null.
*/
public ArrayEnumeration(final Object[] objectarray)
{
if (objectarray == null)
{
throw new NullPointerException("The array must not be null.");
}
this.objectarray = objectarray;
}
/**
* Returns true if this enumeration has at least one more Element.
*
* @return true, if there are more elements, false otherwise.
*/
public boolean hasMoreElements()
{
return (counter < objectarray.length);
}
/**
* Returns the next element in the Array.
*
* @return the next element in the array.
* @throws NoSuchElementException if no more elements exist.
*/
public Object nextElement()
{
if (counter >= objectarray.length)
{
throw new NoSuchElementException();
}
final Object retval = objectarray[counter];
counter += 1;
return retval;
}
}
Concatenates the content of two enumerations into one.
/*
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
*
* Copyright 1997-2007 Sun Microsystems, Inc. All rights reserved.
*
* The contents of this file are subject to the terms of either the GNU
* General Public License Version 2 only ("GPL") or the Common
* Development and Distribution License("CDDL") (collectively, the
* "License"). You may not use this file except in compliance with the
* License. You can obtain a copy of the License at
* http://www.netbeans.org/cddl-gplv2.html
* or nbbuild/licenses/CDDL-GPL-2-CP. See the License for the
* specific language governing permissions and limitations under the
* License. When distributing the software, include this License Header
* Notice in each file and include the License file at
* nbbuild/licenses/CDDL-GPL-2-CP. Sun designates this
* particular file as subject to the "Classpath" exception as provided
* by Sun in the GPL Version 2 section of the License file that
* accompanied this code. If applicable, add the following below the
* License Header, with the fields enclosed by brackets [] replaced by
* your own identifying information:
* "Portions Copyrighted [year] [name of copyright owner]"
*
* Contributor(s):
*
* The Original Software is NetBeans. The Initial Developer of the Original
* Software is Sun Microsystems, Inc. Portions Copyright 1997-2006 Sun
* Microsystems, Inc. All Rights Reserved.
*
* If you wish your version of this file to be governed by only the CDDL
* or only the GPL Version 2, indicate your decision by adding
* "[Contributor] elects to include this software in this distribution
* under the [CDDL or GPL Version 2] license." If you do not indicate a
* single choice of license, a recipient has the option to distribute
* your version of this file under either the CDDL, the GPL Version 2 or
* to extend the choice of license to its licensees as provided above.
* However, if you add GPL Version 2 code and therefore, elected the GPL
* Version 2 license, then the option applies only if the new code is
* made subject to such option by the copyright holder.
*/
import java.util.ArrayList;
import java.util.Collections;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.NoSuchElementException;
/**
* @since 4.37
* @author Jaroslav Tulach
*/
public class Utils {
/**
* Concatenates the content of two enumerations into one.
* Until the
* end of <code>en1</code> is reached its elements are being served.
* As soon as the <code>en1</code> has no more elements, the content
* of <code>en2</code> is being returned.
*
* @param en1 first enumeration
* @param en2 second enumeration
* @return enumeration
*/
public static <T> Enumeration<T> concat(Enumeration<? extends T> en1, Enumeration<? extends T> en2) {
ArrayList<Enumeration<? extends T>> two = new ArrayList<Enumeration<? extends T>>();
two.add(en1);
two.add(en2);
return new SeqEn<T>(Collections.enumeration(two));
}
}
class SeqEn<T> extends Object implements Enumeration<T> {
/** enumeration of Enumerations */
private Enumeration<? extends Enumeration<? extends T>> en;
/** current enumeration */
private Enumeration<? extends T> current;
/** is {@link #current} up-to-date and has more elements?
* The combination <CODE>current == null</CODE> and
* <CODE>checked == true means there are no more elements
* in this enumeration.
*/
private boolean checked = false;
/** Constructs new enumeration from already existing. The elements
* of <CODE>en</CODE> should be also enumerations. The resulting
* enumeration contains elements of such enumerations.
*
* @param en enumeration of Enumerations that should be sequenced
*/
public SeqEn(Enumeration<? extends Enumeration <? extends T>> en) {
this.en = en;
}
/** Ensures that current enumeration is set. If there aren"t more
* elements in the Enumerations, sets the field <CODE>current</CODE> to null.
*/
private void ensureCurrent() {
while ((current == null) || !current.hasMoreElements()) {
if (en.hasMoreElements()) {
current = en.nextElement();
} else {
// no next valid enumeration
current = null;
return;
}
}
}
/** @return true if we have more elements */
public boolean hasMoreElements() {
if (!checked) {
ensureCurrent();
checked = true;
}
return current != null;
}
/** @return next element
* @exception NoSuchElementException if there is no next element
*/
public T nextElement() {
if (!checked) {
ensureCurrent();
}
if (current != null) {
checked = false;
return current.nextElement();
} else {
checked = true;
throw new java.util.NoSuchElementException();
}
}
}
Creating Custom Enumerations
import java.lang.reflect.Array;
import java.util.Enumeration;
class ArrayEnumeration implements Enumeration {
private final int size;
private int cursor;
private final Object array;
public ArrayEnumeration(Object obj) {
Class type = obj.getClass();
if (!type.isArray()) {
throw new IllegalArgumentException("Invalid type: " + type);
}
size = Array.getLength(obj);
array = obj;
}
public boolean hasMoreElements() {
return (cursor < size);
}
public Object nextElement() {
return Array.get(array, cursor++);
}
}
public class MainClass {
public static void main(String args[]) {
Object obj = new int[] { 2, 3, 5, 8, 13, 21 };
Enumeration e = new ArrayEnumeration(obj);
while (e.hasMoreElements()) {
System.out.println(e.nextElement());
}
try {
e = new ArrayEnumeration("Not an Array");
} catch (IllegalArgumentException ex) {
System.out.println(ex.getMessage());
}
}
}
2 3 5 8 13 21 Invalid type: class java.lang.String
Filters enumeration to contain each of the provided elements just once.
/*
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
*
* Copyright 1997-2007 Sun Microsystems, Inc. All rights reserved.
*
* The contents of this file are subject to the terms of either the GNU
* General Public License Version 2 only ("GPL") or the Common
* Development and Distribution License("CDDL") (collectively, the
* "License"). You may not use this file except in compliance with the
* License. You can obtain a copy of the License at
* http://www.netbeans.org/cddl-gplv2.html
* or nbbuild/licenses/CDDL-GPL-2-CP. See the License for the
* specific language governing permissions and limitations under the
* License. When distributing the software, include this License Header
* Notice in each file and include the License file at
* nbbuild/licenses/CDDL-GPL-2-CP. Sun designates this
* particular file as subject to the "Classpath" exception as provided
* by Sun in the GPL Version 2 section of the License file that
* accompanied this code. If applicable, add the following below the
* License Header, with the fields enclosed by brackets [] replaced by
* your own identifying information:
* "Portions Copyrighted [year] [name of copyright owner]"
*
* Contributor(s):
*
* The Original Software is NetBeans. The Initial Developer of the Original
* Software is Sun Microsystems, Inc. Portions Copyright 1997-2006 Sun
* Microsystems, Inc. All Rights Reserved.
*
* If you wish your version of this file to be governed by only the CDDL
* or only the GPL Version 2, indicate your decision by adding
* "[Contributor] elects to include this software in this distribution
* under the [CDDL or GPL Version 2] license." If you do not indicate a
* single choice of license, a recipient has the option to distribute
* your version of this file under either the CDDL, the GPL Version 2 or
* to extend the choice of license to its licensees as provided above.
* However, if you add GPL Version 2 code and therefore, elected the GPL
* Version 2 license, then the option applies only if the new code is
* made subject to such option by the copyright holder.
*/
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Enumeration;
import java.util.HashSet;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Set;
/**
* @since 4.37
* @author Jaroslav Tulach
*/
final class Enumerations extends Object {
/**
* Filters the input enumeration to new one that should contain
* each of the provided elements just once.
* The elements are compared
* using their default <code>equals</code> and <code>hashCode</code> methods.
*
* @param en enumeration to filter
* @return enumeration without duplicated items
*/
public static <T> Enumeration<T> removeDuplicates(Enumeration<T> en) {
class RDupls implements Processor<T,T> {
private Set<T> set = new HashSet<T>();
public T process(T o, Collection<T> nothing) {
return set.add(o) ? o : null;
}
}
return filter(en, new RDupls());
}
/**
* Returns an enumeration that iterates over provided array.
* @param arr the array of object
* @return enumeration of those objects
*/
public static <T> Enumeration<T> array(T... arr) {
return Collections.enumeration(Arrays.asList(arr));
}
/**
* Removes all <code>null</code>s from the input enumeration.
* @param en enumeration that can contain nulls
* @return new enumeration without null values
*/
public static <T> Enumeration<T> removeNulls(Enumeration<T> en) {
return filter(en, new RNulls<T>());
}
/**
* For each element of the input enumeration <code>en</code> asks the
* {@link Processor} to provide a replacement.
* The <code>toAdd</code> argument of the processor is always null.
*
* Example to convert any objects into strings:
* <pre>
* Processor convertToString = new Processor() {
* public Object process(Object obj, Collection alwaysNull) {
* return obj.toString(); // converts to string
* }
* };
* Enumeration strings = Enumerations.convert(elems, convertToString);
* </pre>
*
* @param en enumeration of any objects
* @param processor a callback processor for the elements (its toAdd arguments is always null)
* @return new enumeration where all elements has been processed
*/
public static <T,R> Enumeration<R> convert(Enumeration<? extends T> en, Processor<T,R> processor) {
return new AltEn<T,R>(en, processor);
}
/**
* Filters some elements out from the input enumeration.
* Just make the
* {@link Processor} return <code>null</code>. Please notice the <code>toAdd</code>
* argument of the processor is always <code>null</code>.
*
* Example to remove all objects that are not strings:
* <pre>
* Processor onlyString = new Processor() {
* public Object process(Object obj, Collection alwaysNull) {
* if (obj instanceof String) {
* return obj;
* } else {
* return null;
* }
* }
* };
* Enumeration strings = Enumerations.filter(elems, onlyString);
* </pre>
*
* @param en enumeration of any objects
* @param filter a callback processor for the elements (its toAdd arguments is always null)
* @return new enumeration which does not include non-processed (returned null from processor) elements
* @see NbCollections#checkedEnumerationByFilter
*/
public static <T,R> Enumeration<R> filter(Enumeration<? extends T> en, Processor<T,R> filter) {
return new FilEn<T,R>(en, filter);
}
/**
* Support for breadth-first enumerating.
* Before any element is returned
* for the resulting enumeration it is processed in the {@link Processor} and
* the processor is allowed to modify it and also add additional elements
* at the (current) end of the <q>queue</q> by calling <code>toAdd.add</code>
* or <code>toAdd.addAll</code>. No other methods can be called on the
* provided <code>toAdd</code> collection.
*
* Example of doing breadth-first walk through a tree:
* <pre>
* Processor queueSubnodes = new Processor() {
* public Object process(Object obj, Collection toAdd) {
* Node n = (Node)obj;
* toAdd.addAll (n.getChildrenList());
* return n;
* }
* };
* Enumeration strings = Enumerations.queue(elems, queueSubnodes);
* </pre>
*
* @param en initial content of the resulting enumeration
* @param filter the processor that is called for each element and can
* add and addAll elements to its toAdd Collection argument and
* also change the value to be returned
* @return enumeration with the initial and queued content (it can contain
* <code>null</code> if the filter returned <code>null</code> from its
* {@link Processor#process} method.
*/
public static <T,R> Enumeration<R> queue(Enumeration<? extends T> en, Processor<T,R> filter) {
QEn<T,R> q = new QEn<T,R>(filter);
while (en.hasMoreElements()) {
q.put(en.nextElement());
}
return q;
}
/**
* Processor interface that can filter out objects from the enumeration,
* change them or add aditional objects to the end of the current enumeration.
*/
public static interface Processor<T,R> {
/** @param original the object that is going to be returned from the enumeration right now
* @return a replacement for this object
* @param toAdd can be non-null if one can add new objects at the end of the enumeration
*/
public R process(T original, Collection<T> toAdd);
}
/** Altering enumeration implementation */
private static final class AltEn<T,R> extends Object implements Enumeration<R> {
/** enumeration to filter */
private Enumeration<? extends T> en;
/** map to alter */
private Processor<T,R> process;
/**
* @param en enumeration to filter
*/
public AltEn(Enumeration<? extends T> en, Processor<T,R> process) {
this.en = en;
this.process = process;
}
/** @return true if there is more elements in the enumeration
*/
public boolean hasMoreElements() {
return en.hasMoreElements();
}
/** @return next object in the enumeration
* @exception NoSuchElementException can be thrown if there is no next object
* in the enumeration
*/
public R nextElement() {
return process.process(en.nextElement(), null);
}
}
// end of AltEn
/** QueueEnumeration
*/
private static class QEn<T,R> extends Object implements Enumeration<R> {
/** next object to be returned */
private ListItem<T> next = null;
/** last object in the queue */
private ListItem<T> last = null;
/** processor to use */
private Processor<T,R> processor;
public QEn(Processor<T,R> p) {
this.processor = p;
}
/** Put adds new object to the end of queue.
* @param o the object to add
*/
public void put(T o) {
if (last != null) {
ListItem<T> li = new ListItem<T>(o);
last.next = li;
last = li;
} else {
next = last = new ListItem<T>(o);
}
}
/** Adds array of objects into the queue.
* @param arr array of objects to put into the queue
*/
public void put(Collection<? extends T> arr) {
for (T e : arr) {
put(e);
}
}
/** Is there any next object?
* @return true if there is next object, false otherwise
*/
public boolean hasMoreElements() {
return next != null;
}
/** @return next object in enumeration
* @exception NoSuchElementException if there is no next object
*/
public R nextElement() {
if (next == null) {
throw new NoSuchElementException();
}
T res = next.object;
if ((next = next.next) == null) {
last = null;
}
;
ToAdd<T,R> toAdd = new ToAdd<T,R>(this);
R out = processor.process(res, toAdd);
toAdd.finish();
return out;
}
/** item in linked list of Objects */
private static final class ListItem<T> {
T object;
ListItem<T> next;
/** @param o the object for this item */
ListItem(T o) {
object = o;
}
}
/** Temporary collection that supports only add and addAll operations*/
private static final class ToAdd<T,R> extends Object implements Collection<T> {
private QEn<T,R> q;
public ToAdd(QEn<T,R> q) {
this.q = q;
}
public void finish() {
this.q = null;
}
public boolean add(T o) {
q.put(o);
return true;
}
public boolean addAll(Collection<? extends T> c) {
q.put(c);
return true;
}
private String msg() {
return "Only add and addAll are implemented"; // NOI18N
}
public void clear() {
throw new UnsupportedOperationException(msg());
}
public boolean contains(Object o) {
throw new UnsupportedOperationException(msg());
}
public boolean containsAll(Collection c) {
throw new UnsupportedOperationException(msg());
}
public boolean isEmpty() {
throw new UnsupportedOperationException(msg());
}
public Iterator<T> iterator() {
throw new UnsupportedOperationException(msg());
}
public boolean remove(Object o) {
throw new UnsupportedOperationException(msg());
}
public boolean removeAll(Collection c) {
throw new UnsupportedOperationException(msg());
}
public boolean retainAll(Collection c) {
throw new UnsupportedOperationException(msg());
}
public int size() {
throw new UnsupportedOperationException(msg());
}
public Object[] toArray() {
throw new UnsupportedOperationException(msg());
}
public<X> X[] toArray(X[] a) {
throw new UnsupportedOperationException(msg());
}
}
// end of ToAdd
}
// end of QEn
/** Filtering enumeration */
private static final class FilEn<T,R> extends Object implements Enumeration<R> {
/** marker object stating there is no nexte element prepared */
private static final Object EMPTY = new Object();
/** enumeration to filter */
private Enumeration<? extends T> en;
/** element to be returned next time or {@link #EMPTY} if there is
* no such element prepared */
private R next = empty();
/** the set to use as filter */
private Processor<T,R> filter;
/**
* @param en enumeration to filter
*/
public FilEn(Enumeration<? extends T> en, Processor<T,R> filter) {
this.en = en;
this.filter = filter;
}
/** @return true if there is more elements in the enumeration
*/
public boolean hasMoreElements() {
if (next != empty()) {
// there is a object already prepared
return true;
}
while (en.hasMoreElements()) {
// read next
next = filter.process(en.nextElement(), null);
if (next != null) {
// if the object is accepted
return true;
}
;
}
next = empty();
return false;
}
/** @return next object in the enumeration
* @exception NoSuchElementException can be thrown if there is no next object
* in the enumeration
*/
public R nextElement() {
if ((next == EMPTY) && !hasMoreElements()) {
throw new NoSuchElementException();
}
R res = next;
next = empty();
return res;
}
@SuppressWarnings("unchecked")
private R empty() {
return (R)EMPTY;
}
}
// end of FilEn
/** Returns true from contains if object is not null */
private static class RNulls<T> implements Processor<T,T> {
public T process(T original, Collection<T> toAdd) {
return original;
}
}
// end of RNulls
}
Filters some elements out from the input enumeration.
/*
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
*
* Copyright 1997-2007 Sun Microsystems, Inc. All rights reserved.
*
* The contents of this file are subject to the terms of either the GNU
* General Public License Version 2 only ("GPL") or the Common
* Development and Distribution License("CDDL") (collectively, the
* "License"). You may not use this file except in compliance with the
* License. You can obtain a copy of the License at
* http://www.netbeans.org/cddl-gplv2.html
* or nbbuild/licenses/CDDL-GPL-2-CP. See the License for the
* specific language governing permissions and limitations under the
* License. When distributing the software, include this License Header
* Notice in each file and include the License file at
* nbbuild/licenses/CDDL-GPL-2-CP. Sun designates this
* particular file as subject to the "Classpath" exception as provided
* by Sun in the GPL Version 2 section of the License file that
* accompanied this code. If applicable, add the following below the
* License Header, with the fields enclosed by brackets [] replaced by
* your own identifying information:
* "Portions Copyrighted [year] [name of copyright owner]"
*
* Contributor(s):
*
* The Original Software is NetBeans. The Initial Developer of the Original
* Software is Sun Microsystems, Inc. Portions Copyright 1997-2006 Sun
* Microsystems, Inc. All Rights Reserved.
*
* If you wish your version of this file to be governed by only the CDDL
* or only the GPL Version 2, indicate your decision by adding
* "[Contributor] elects to include this software in this distribution
* under the [CDDL or GPL Version 2] license." If you do not indicate a
* single choice of license, a recipient has the option to distribute
* your version of this file under either the CDDL, the GPL Version 2 or
* to extend the choice of license to its licensees as provided above.
* However, if you add GPL Version 2 code and therefore, elected the GPL
* Version 2 license, then the option applies only if the new code is
* made subject to such option by the copyright holder.
*/
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Enumeration;
import java.util.HashSet;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Set;
/**
* @since 4.37
* @author Jaroslav Tulach
*/
final class Enumerations extends Object {
/**
* Filters some elements out from the input enumeration.
* Just make the
* {@link Processor} return <code>null</code>. Please notice the <code>toAdd</code>
* argument of the processor is always <code>null</code>.
*
* Example to remove all objects that are not strings:
* <pre>
* Processor onlyString = new Processor() {
* public Object process(Object obj, Collection alwaysNull) {
* if (obj instanceof String) {
* return obj;
* } else {
* return null;
* }
* }
* };
* Enumeration strings = Enumerations.filter(elems, onlyString);
* </pre>
*
* @param en enumeration of any objects
* @param filter a callback processor for the elements (its toAdd arguments is always null)
* @return new enumeration which does not include non-processed (returned null from processor) elements
* @see NbCollections#checkedEnumerationByFilter
*/
public static <T,R> Enumeration<R> filter(Enumeration<? extends T> en, Processor<T,R> filter) {
return new FilEn<T,R>(en, filter);
}
/**
* Support for breadth-first enumerating.
* Before any element is returned
* for the resulting enumeration it is processed in the {@link Processor} and
* the processor is allowed to modify it and also add additional elements
* at the (current) end of the <q>queue</q> by calling <code>toAdd.add</code>
* or <code>toAdd.addAll</code>. No other methods can be called on the
* provided <code>toAdd</code> collection.
*
* Example of doing breadth-first walk through a tree:
* <pre>
* Processor queueSubnodes = new Processor() {
* public Object process(Object obj, Collection toAdd) {
* Node n = (Node)obj;
* toAdd.addAll (n.getChildrenList());
* return n;
* }
* };
* Enumeration strings = Enumerations.queue(elems, queueSubnodes);
* </pre>
*
* @param en initial content of the resulting enumeration
* @param filter the processor that is called for each element and can
* add and addAll elements to its toAdd Collection argument and
* also change the value to be returned
* @return enumeration with the initial and queued content (it can contain
* <code>null</code> if the filter returned <code>null</code> from its
* {@link Processor#process} method.
*/
public static <T,R> Enumeration<R> queue(Enumeration<? extends T> en, Processor<T,R> filter) {
QEn<T,R> q = new QEn<T,R>(filter);
while (en.hasMoreElements()) {
q.put(en.nextElement());
}
return q;
}
/**
* Processor interface that can filter out objects from the enumeration,
* change them or add aditional objects to the end of the current enumeration.
*/
public static interface Processor<T,R> {
/** @param original the object that is going to be returned from the enumeration right now
* @return a replacement for this object
* @param toAdd can be non-null if one can add new objects at the end of the enumeration
*/
public R process(T original, Collection<T> toAdd);
}
/** Altering enumeration implementation */
private static final class AltEn<T,R> extends Object implements Enumeration<R> {
/** enumeration to filter */
private Enumeration<? extends T> en;
/** map to alter */
private Processor<T,R> process;
/**
* @param en enumeration to filter
*/
public AltEn(Enumeration<? extends T> en, Processor<T,R> process) {
this.en = en;
this.process = process;
}
/** @return true if there is more elements in the enumeration
*/
public boolean hasMoreElements() {
return en.hasMoreElements();
}
/** @return next object in the enumeration
* @exception NoSuchElementException can be thrown if there is no next object
* in the enumeration
*/
public R nextElement() {
return process.process(en.nextElement(), null);
}
}
// end of AltEn
/** QueueEnumeration
*/
private static class QEn<T,R> extends Object implements Enumeration<R> {
/** next object to be returned */
private ListItem<T> next = null;
/** last object in the queue */
private ListItem<T> last = null;
/** processor to use */
private Processor<T,R> processor;
public QEn(Processor<T,R> p) {
this.processor = p;
}
/** Put adds new object to the end of queue.
* @param o the object to add
*/
public void put(T o) {
if (last != null) {
ListItem<T> li = new ListItem<T>(o);
last.next = li;
last = li;
} else {
next = last = new ListItem<T>(o);
}
}
/** Adds array of objects into the queue.
* @param arr array of objects to put into the queue
*/
public void put(Collection<? extends T> arr) {
for (T e : arr) {
put(e);
}
}
/** Is there any next object?
* @return true if there is next object, false otherwise
*/
public boolean hasMoreElements() {
return next != null;
}
/** @return next object in enumeration
* @exception NoSuchElementException if there is no next object
*/
public R nextElement() {
if (next == null) {
throw new NoSuchElementException();
}
T res = next.object;
if ((next = next.next) == null) {
last = null;
}
;
ToAdd<T,R> toAdd = new ToAdd<T,R>(this);
R out = processor.process(res, toAdd);
toAdd.finish();
return out;
}
/** item in linked list of Objects */
private static final class ListItem<T> {
T object;
ListItem<T> next;
/** @param o the object for this item */
ListItem(T o) {
object = o;
}
}
/** Temporary collection that supports only add and addAll operations*/
private static final class ToAdd<T,R> extends Object implements Collection<T> {
private QEn<T,R> q;
public ToAdd(QEn<T,R> q) {
this.q = q;
}
public void finish() {
this.q = null;
}
public boolean add(T o) {
q.put(o);
return true;
}
public boolean addAll(Collection<? extends T> c) {
q.put(c);
return true;
}
private String msg() {
return "Only add and addAll are implemented"; // NOI18N
}
public void clear() {
throw new UnsupportedOperationException(msg());
}
public boolean contains(Object o) {
throw new UnsupportedOperationException(msg());
}
public boolean containsAll(Collection c) {
throw new UnsupportedOperationException(msg());
}
public boolean isEmpty() {
throw new UnsupportedOperationException(msg());
}
public Iterator<T> iterator() {
throw new UnsupportedOperationException(msg());
}
public boolean remove(Object o) {
throw new UnsupportedOperationException(msg());
}
public boolean removeAll(Collection c) {
throw new UnsupportedOperationException(msg());
}
public boolean retainAll(Collection c) {
throw new UnsupportedOperationException(msg());
}
public int size() {
throw new UnsupportedOperationException(msg());
}
public Object[] toArray() {
throw new UnsupportedOperationException(msg());
}
public<X> X[] toArray(X[] a) {
throw new UnsupportedOperationException(msg());
}
}
// end of ToAdd
}
// end of QEn
/** Filtering enumeration */
private static final class FilEn<T,R> extends Object implements Enumeration<R> {
/** marker object stating there is no nexte element prepared */
private static final Object EMPTY = new Object();
/** enumeration to filter */
private Enumeration<? extends T> en;
/** element to be returned next time or {@link #EMPTY} if there is
* no such element prepared */
private R next = empty();
/** the set to use as filter */
private Processor<T,R> filter;
/**
* @param en enumeration to filter
*/
public FilEn(Enumeration<? extends T> en, Processor<T,R> filter) {
this.en = en;
this.filter = filter;
}
/** @return true if there is more elements in the enumeration
*/
public boolean hasMoreElements() {
if (next != empty()) {
// there is a object already prepared
return true;
}
while (en.hasMoreElements()) {
// read next
next = filter.process(en.nextElement(), null);
if (next != null) {
// if the object is accepted
return true;
}
;
}
next = empty();
return false;
}
/** @return next object in the enumeration
* @exception NoSuchElementException can be thrown if there is no next object
* in the enumeration
*/
public R nextElement() {
if ((next == EMPTY) && !hasMoreElements()) {
throw new NoSuchElementException();
}
R res = next;
next = empty();
return res;
}
@SuppressWarnings("unchecked")
private R empty() {
return (R)EMPTY;
}
}
// end of FilEn
/** Returns true from contains if object is not null */
private static class RNulls<T> implements Processor<T,T> {
public T process(T original, Collection<T> toAdd) {
return original;
}
}
// end of RNulls
}
For each element of the input enumeration asks the Processor to provide a replacement
/*
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
*
* Copyright 1997-2007 Sun Microsystems, Inc. All rights reserved.
*
* The contents of this file are subject to the terms of either the GNU
* General Public License Version 2 only ("GPL") or the Common
* Development and Distribution License("CDDL") (collectively, the
* "License"). You may not use this file except in compliance with the
* License. You can obtain a copy of the License at
* http://www.netbeans.org/cddl-gplv2.html
* or nbbuild/licenses/CDDL-GPL-2-CP. See the License for the
* specific language governing permissions and limitations under the
* License. When distributing the software, include this License Header
* Notice in each file and include the License file at
* nbbuild/licenses/CDDL-GPL-2-CP. Sun designates this
* particular file as subject to the "Classpath" exception as provided
* by Sun in the GPL Version 2 section of the License file that
* accompanied this code. If applicable, add the following below the
* License Header, with the fields enclosed by brackets [] replaced by
* your own identifying information:
* "Portions Copyrighted [year] [name of copyright owner]"
*
* Contributor(s):
*
* The Original Software is NetBeans. The Initial Developer of the Original
* Software is Sun Microsystems, Inc. Portions Copyright 1997-2006 Sun
* Microsystems, Inc. All Rights Reserved.
*
* If you wish your version of this file to be governed by only the CDDL
* or only the GPL Version 2, indicate your decision by adding
* "[Contributor] elects to include this software in this distribution
* under the [CDDL or GPL Version 2] license." If you do not indicate a
* single choice of license, a recipient has the option to distribute
* your version of this file under either the CDDL, the GPL Version 2 or
* to extend the choice of license to its licensees as provided above.
* However, if you add GPL Version 2 code and therefore, elected the GPL
* Version 2 license, then the option applies only if the new code is
* made subject to such option by the copyright holder.
*/
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Enumeration;
import java.util.HashSet;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Set;
/**
* @since 4.37
* @author Jaroslav Tulach
*/
final class Enumerations extends Object {
/**
* For each element of the input enumeration <code>en</code> asks the
* {@link Processor} to provide a replacement.
* The <code>toAdd</code> argument of the processor is always null.
*
* Example to convert any objects into strings:
* <pre>
* Processor convertToString = new Processor() {
* public Object process(Object obj, Collection alwaysNull) {
* return obj.toString(); // converts to string
* }
* };
* Enumeration strings = Enumerations.convert(elems, convertToString);
* </pre>
*
* @param en enumeration of any objects
* @param processor a callback processor for the elements (its toAdd arguments is always null)
* @return new enumeration where all elements has been processed
*/
public static <T,R> Enumeration<R> convert(Enumeration<? extends T> en, Processor<T,R> processor) {
return new AltEn<T,R>(en, processor);
}
/**
* Filters some elements out from the input enumeration.
* Just make the
* {@link Processor} return <code>null</code>. Please notice the <code>toAdd</code>
* argument of the processor is always <code>null</code>.
*
* Example to remove all objects that are not strings:
* <pre>
* Processor onlyString = new Processor() {
* public Object process(Object obj, Collection alwaysNull) {
* if (obj instanceof String) {
* return obj;
* } else {
* return null;
* }
* }
* };
* Enumeration strings = Enumerations.filter(elems, onlyString);
* </pre>
*
* @param en enumeration of any objects
* @param filter a callback processor for the elements (its toAdd arguments is always null)
* @return new enumeration which does not include non-processed (returned null from processor) elements
* @see NbCollections#checkedEnumerationByFilter
*/
public static <T,R> Enumeration<R> filter(Enumeration<? extends T> en, Processor<T,R> filter) {
return new FilEn<T,R>(en, filter);
}
/**
* Support for breadth-first enumerating.
* Before any element is returned
* for the resulting enumeration it is processed in the {@link Processor} and
* the processor is allowed to modify it and also add additional elements
* at the (current) end of the <q>queue</q> by calling <code>toAdd.add</code>
* or <code>toAdd.addAll</code>. No other methods can be called on the
* provided <code>toAdd</code> collection.
*
* Example of doing breadth-first walk through a tree:
* <pre>
* Processor queueSubnodes = new Processor() {
* public Object process(Object obj, Collection toAdd) {
* Node n = (Node)obj;
* toAdd.addAll (n.getChildrenList());
* return n;
* }
* };
* Enumeration strings = Enumerations.queue(elems, queueSubnodes);
* </pre>
*
* @param en initial content of the resulting enumeration
* @param filter the processor that is called for each element and can
* add and addAll elements to its toAdd Collection argument and
* also change the value to be returned
* @return enumeration with the initial and queued content (it can contain
* <code>null</code> if the filter returned <code>null</code> from its
* {@link Processor#process} method.
*/
public static <T,R> Enumeration<R> queue(Enumeration<? extends T> en, Processor<T,R> filter) {
QEn<T,R> q = new QEn<T,R>(filter);
while (en.hasMoreElements()) {
q.put(en.nextElement());
}
return q;
}
/**
* Processor interface that can filter out objects from the enumeration,
* change them or add aditional objects to the end of the current enumeration.
*/
public static interface Processor<T,R> {
/** @param original the object that is going to be returned from the enumeration right now
* @return a replacement for this object
* @param toAdd can be non-null if one can add new objects at the end of the enumeration
*/
public R process(T original, Collection<T> toAdd);
}
/** Altering enumeration implementation */
private static final class AltEn<T,R> extends Object implements Enumeration<R> {
/** enumeration to filter */
private Enumeration<? extends T> en;
/** map to alter */
private Processor<T,R> process;
/**
* @param en enumeration to filter
*/
public AltEn(Enumeration<? extends T> en, Processor<T,R> process) {
this.en = en;
this.process = process;
}
/** @return true if there is more elements in the enumeration
*/
public boolean hasMoreElements() {
return en.hasMoreElements();
}
/** @return next object in the enumeration
* @exception NoSuchElementException can be thrown if there is no next object
* in the enumeration
*/
public R nextElement() {
return process.process(en.nextElement(), null);
}
}
// end of AltEn
/** QueueEnumeration
*/
private static class QEn<T,R> extends Object implements Enumeration<R> {
/** next object to be returned */
private ListItem<T> next = null;
/** last object in the queue */
private ListItem<T> last = null;
/** processor to use */
private Processor<T,R> processor;
public QEn(Processor<T,R> p) {
this.processor = p;
}
/** Put adds new object to the end of queue.
* @param o the object to add
*/
public void put(T o) {
if (last != null) {
ListItem<T> li = new ListItem<T>(o);
last.next = li;
last = li;
} else {
next = last = new ListItem<T>(o);
}
}
/** Adds array of objects into the queue.
* @param arr array of objects to put into the queue
*/
public void put(Collection<? extends T> arr) {
for (T e : arr) {
put(e);
}
}
/** Is there any next object?
* @return true if there is next object, false otherwise
*/
public boolean hasMoreElements() {
return next != null;
}
/** @return next object in enumeration
* @exception NoSuchElementException if there is no next object
*/
public R nextElement() {
if (next == null) {
throw new NoSuchElementException();
}
T res = next.object;
if ((next = next.next) == null) {
last = null;
}
;
ToAdd<T,R> toAdd = new ToAdd<T,R>(this);
R out = processor.process(res, toAdd);
toAdd.finish();
return out;
}
/** item in linked list of Objects */
private static final class ListItem<T> {
T object;
ListItem<T> next;
/** @param o the object for this item */
ListItem(T o) {
object = o;
}
}
/** Temporary collection that supports only add and addAll operations*/
private static final class ToAdd<T,R> extends Object implements Collection<T> {
private QEn<T,R> q;
public ToAdd(QEn<T,R> q) {
this.q = q;
}
public void finish() {
this.q = null;
}
public boolean add(T o) {
q.put(o);
return true;
}
public boolean addAll(Collection<? extends T> c) {
q.put(c);
return true;
}
private String msg() {
return "Only add and addAll are implemented"; // NOI18N
}
public void clear() {
throw new UnsupportedOperationException(msg());
}
public boolean contains(Object o) {
throw new UnsupportedOperationException(msg());
}
public boolean containsAll(Collection c) {
throw new UnsupportedOperationException(msg());
}
public boolean isEmpty() {
throw new UnsupportedOperationException(msg());
}
public Iterator<T> iterator() {
throw new UnsupportedOperationException(msg());
}
public boolean remove(Object o) {
throw new UnsupportedOperationException(msg());
}
public boolean removeAll(Collection c) {
throw new UnsupportedOperationException(msg());
}
public boolean retainAll(Collection c) {
throw new UnsupportedOperationException(msg());
}
public int size() {
throw new UnsupportedOperationException(msg());
}
public Object[] toArray() {
throw new UnsupportedOperationException(msg());
}
public<X> X[] toArray(X[] a) {
throw new UnsupportedOperationException(msg());
}
}
// end of ToAdd
}
// end of QEn
/** Filtering enumeration */
private static final class FilEn<T,R> extends Object implements Enumeration<R> {
/** marker object stating there is no nexte element prepared */
private static final Object EMPTY = new Object();
/** enumeration to filter */
private Enumeration<? extends T> en;
/** element to be returned next time or {@link #EMPTY} if there is
* no such element prepared */
private R next = empty();
/** the set to use as filter */
private Processor<T,R> filter;
/**
* @param en enumeration to filter
*/
public FilEn(Enumeration<? extends T> en, Processor<T,R> filter) {
this.en = en;
this.filter = filter;
}
/** @return true if there is more elements in the enumeration
*/
public boolean hasMoreElements() {
if (next != empty()) {
// there is a object already prepared
return true;
}
while (en.hasMoreElements()) {
// read next
next = filter.process(en.nextElement(), null);
if (next != null) {
// if the object is accepted
return true;
}
;
}
next = empty();
return false;
}
/** @return next object in the enumeration
* @exception NoSuchElementException can be thrown if there is no next object
* in the enumeration
*/
public R nextElement() {
if ((next == EMPTY) && !hasMoreElements()) {
throw new NoSuchElementException();
}
R res = next;
next = empty();
return res;
}
@SuppressWarnings("unchecked")
private R empty() {
return (R)EMPTY;
}
}
// end of FilEn
/** Returns true from contains if object is not null */
private static class RNulls<T> implements Processor<T,T> {
public T process(T original, Collection<T> toAdd) {
return original;
}
}
// end of RNulls
}
If you prefer a for-loop
import java.util.Enumeration;
import java.util.Vector;
public class MainClass {
public static void main(String args[]) throws Exception {
Vector v = new Vector();
v.add("a");
v.add("b");
v.add("c");
for (Enumeration e = v.elements(); e.hasMoreElements();) {
Object o = e.nextElement();
System.out.println(o);
}
}
}
a b c
Removes all nulls from the input enumeration.
/*
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
*
* Copyright 1997-2007 Sun Microsystems, Inc. All rights reserved.
*
* The contents of this file are subject to the terms of either the GNU
* General Public License Version 2 only ("GPL") or the Common
* Development and Distribution License("CDDL") (collectively, the
* "License"). You may not use this file except in compliance with the
* License. You can obtain a copy of the License at
* http://www.netbeans.org/cddl-gplv2.html
* or nbbuild/licenses/CDDL-GPL-2-CP. See the License for the
* specific language governing permissions and limitations under the
* License. When distributing the software, include this License Header
* Notice in each file and include the License file at
* nbbuild/licenses/CDDL-GPL-2-CP. Sun designates this
* particular file as subject to the "Classpath" exception as provided
* by Sun in the GPL Version 2 section of the License file that
* accompanied this code. If applicable, add the following below the
* License Header, with the fields enclosed by brackets [] replaced by
* your own identifying information:
* "Portions Copyrighted [year] [name of copyright owner]"
*
* Contributor(s):
*
* The Original Software is NetBeans. The Initial Developer of the Original
* Software is Sun Microsystems, Inc. Portions Copyright 1997-2006 Sun
* Microsystems, Inc. All Rights Reserved.
*
* If you wish your version of this file to be governed by only the CDDL
* or only the GPL Version 2, indicate your decision by adding
* "[Contributor] elects to include this software in this distribution
* under the [CDDL or GPL Version 2] license." If you do not indicate a
* single choice of license, a recipient has the option to distribute
* your version of this file under either the CDDL, the GPL Version 2 or
* to extend the choice of license to its licensees as provided above.
* However, if you add GPL Version 2 code and therefore, elected the GPL
* Version 2 license, then the option applies only if the new code is
* made subject to such option by the copyright holder.
*/
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Enumeration;
import java.util.HashSet;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Set;
/**
* @since 4.37
* @author Jaroslav Tulach
*/
final class Enumerations extends Object {
/**
* Removes all <code>null</code>s from the input enumeration.
* @param en enumeration that can contain nulls
* @return new enumeration without null values
*/
public static <T> Enumeration<T> removeNulls(Enumeration<T> en) {
return filter(en, new RNulls<T>());
}
/**
* For each element of the input enumeration <code>en</code> asks the
* {@link Processor} to provide a replacement.
* The <code>toAdd</code> argument of the processor is always null.
*
* Example to convert any objects into strings:
* <pre>
* Processor convertToString = new Processor() {
* public Object process(Object obj, Collection alwaysNull) {
* return obj.toString(); // converts to string
* }
* };
* Enumeration strings = Enumerations.convert(elems, convertToString);
* </pre>
*
* @param en enumeration of any objects
* @param processor a callback processor for the elements (its toAdd arguments is always null)
* @return new enumeration where all elements has been processed
*/
public static <T,R> Enumeration<R> convert(Enumeration<? extends T> en, Processor<T,R> processor) {
return new AltEn<T,R>(en, processor);
}
/**
* Filters some elements out from the input enumeration.
* Just make the
* {@link Processor} return <code>null</code>. Please notice the <code>toAdd</code>
* argument of the processor is always <code>null</code>.
*
* Example to remove all objects that are not strings:
* <pre>
* Processor onlyString = new Processor() {
* public Object process(Object obj, Collection alwaysNull) {
* if (obj instanceof String) {
* return obj;
* } else {
* return null;
* }
* }
* };
* Enumeration strings = Enumerations.filter(elems, onlyString);
* </pre>
*
* @param en enumeration of any objects
* @param filter a callback processor for the elements (its toAdd arguments is always null)
* @return new enumeration which does not include non-processed (returned null from processor) elements
* @see NbCollections#checkedEnumerationByFilter
*/
public static <T,R> Enumeration<R> filter(Enumeration<? extends T> en, Processor<T,R> filter) {
return new FilEn<T,R>(en, filter);
}
/**
* Support for breadth-first enumerating.
* Before any element is returned
* for the resulting enumeration it is processed in the {@link Processor} and
* the processor is allowed to modify it and also add additional elements
* at the (current) end of the <q>queue</q> by calling <code>toAdd.add</code>
* or <code>toAdd.addAll</code>. No other methods can be called on the
* provided <code>toAdd</code> collection.
*
* Example of doing breadth-first walk through a tree:
* <pre>
* Processor queueSubnodes = new Processor() {
* public Object process(Object obj, Collection toAdd) {
* Node n = (Node)obj;
* toAdd.addAll (n.getChildrenList());
* return n;
* }
* };
* Enumeration strings = Enumerations.queue(elems, queueSubnodes);
* </pre>
*
* @param en initial content of the resulting enumeration
* @param filter the processor that is called for each element and can
* add and addAll elements to its toAdd Collection argument and
* also change the value to be returned
* @return enumeration with the initial and queued content (it can contain
* <code>null</code> if the filter returned <code>null</code> from its
* {@link Processor#process} method.
*/
public static <T,R> Enumeration<R> queue(Enumeration<? extends T> en, Processor<T,R> filter) {
QEn<T,R> q = new QEn<T,R>(filter);
while (en.hasMoreElements()) {
q.put(en.nextElement());
}
return q;
}
/**
* Processor interface that can filter out objects from the enumeration,
* change them or add aditional objects to the end of the current enumeration.
*/
public static interface Processor<T,R> {
/** @param original the object that is going to be returned from the enumeration right now
* @return a replacement for this object
* @param toAdd can be non-null if one can add new objects at the end of the enumeration
*/
public R process(T original, Collection<T> toAdd);
}
/** Altering enumeration implementation */
private static final class AltEn<T,R> extends Object implements Enumeration<R> {
/** enumeration to filter */
private Enumeration<? extends T> en;
/** map to alter */
private Processor<T,R> process;
/**
* @param en enumeration to filter
*/
public AltEn(Enumeration<? extends T> en, Processor<T,R> process) {
this.en = en;
this.process = process;
}
/** @return true if there is more elements in the enumeration
*/
public boolean hasMoreElements() {
return en.hasMoreElements();
}
/** @return next object in the enumeration
* @exception NoSuchElementException can be thrown if there is no next object
* in the enumeration
*/
public R nextElement() {
return process.process(en.nextElement(), null);
}
}
// end of AltEn
/** QueueEnumeration
*/
private static class QEn<T,R> extends Object implements Enumeration<R> {
/** next object to be returned */
private ListItem<T> next = null;
/** last object in the queue */
private ListItem<T> last = null;
/** processor to use */
private Processor<T,R> processor;
public QEn(Processor<T,R> p) {
this.processor = p;
}
/** Put adds new object to the end of queue.
* @param o the object to add
*/
public void put(T o) {
if (last != null) {
ListItem<T> li = new ListItem<T>(o);
last.next = li;
last = li;
} else {
next = last = new ListItem<T>(o);
}
}
/** Adds array of objects into the queue.
* @param arr array of objects to put into the queue
*/
public void put(Collection<? extends T> arr) {
for (T e : arr) {
put(e);
}
}
/** Is there any next object?
* @return true if there is next object, false otherwise
*/
public boolean hasMoreElements() {
return next != null;
}
/** @return next object in enumeration
* @exception NoSuchElementException if there is no next object
*/
public R nextElement() {
if (next == null) {
throw new NoSuchElementException();
}
T res = next.object;
if ((next = next.next) == null) {
last = null;
}
;
ToAdd<T,R> toAdd = new ToAdd<T,R>(this);
R out = processor.process(res, toAdd);
toAdd.finish();
return out;
}
/** item in linked list of Objects */
private static final class ListItem<T> {
T object;
ListItem<T> next;
/** @param o the object for this item */
ListItem(T o) {
object = o;
}
}
/** Temporary collection that supports only add and addAll operations*/
private static final class ToAdd<T,R> extends Object implements Collection<T> {
private QEn<T,R> q;
public ToAdd(QEn<T,R> q) {
this.q = q;
}
public void finish() {
this.q = null;
}
public boolean add(T o) {
q.put(o);
return true;
}
public boolean addAll(Collection<? extends T> c) {
q.put(c);
return true;
}
private String msg() {
return "Only add and addAll are implemented"; // NOI18N
}
public void clear() {
throw new UnsupportedOperationException(msg());
}
public boolean contains(Object o) {
throw new UnsupportedOperationException(msg());
}
public boolean containsAll(Collection c) {
throw new UnsupportedOperationException(msg());
}
public boolean isEmpty() {
throw new UnsupportedOperationException(msg());
}
public Iterator<T> iterator() {
throw new UnsupportedOperationException(msg());
}
public boolean remove(Object o) {
throw new UnsupportedOperationException(msg());
}
public boolean removeAll(Collection c) {
throw new UnsupportedOperationException(msg());
}
public boolean retainAll(Collection c) {
throw new UnsupportedOperationException(msg());
}
public int size() {
throw new UnsupportedOperationException(msg());
}
public Object[] toArray() {
throw new UnsupportedOperationException(msg());
}
public<X> X[] toArray(X[] a) {
throw new UnsupportedOperationException(msg());
}
}
// end of ToAdd
}
// end of QEn
/** Filtering enumeration */
private static final class FilEn<T,R> extends Object implements Enumeration<R> {
/** marker object stating there is no nexte element prepared */
private static final Object EMPTY = new Object();
/** enumeration to filter */
private Enumeration<? extends T> en;
/** element to be returned next time or {@link #EMPTY} if there is
* no such element prepared */
private R next = empty();
/** the set to use as filter */
private Processor<T,R> filter;
/**
* @param en enumeration to filter
*/
public FilEn(Enumeration<? extends T> en, Processor<T,R> filter) {
this.en = en;
this.filter = filter;
}
/** @return true if there is more elements in the enumeration
*/
public boolean hasMoreElements() {
if (next != empty()) {
// there is a object already prepared
return true;
}
while (en.hasMoreElements()) {
// read next
next = filter.process(en.nextElement(), null);
if (next != null) {
// if the object is accepted
return true;
}
;
}
next = empty();
return false;
}
/** @return next object in the enumeration
* @exception NoSuchElementException can be thrown if there is no next object
* in the enumeration
*/
public R nextElement() {
if ((next == EMPTY) && !hasMoreElements()) {
throw new NoSuchElementException();
}
R res = next;
next = empty();
return res;
}
@SuppressWarnings("unchecked")
private R empty() {
return (R)EMPTY;
}
}
// end of FilEn
/** Returns true from contains if object is not null */
private static class RNulls<T> implements Processor<T,T> {
public T process(T original, Collection<T> toAdd) {
return original;
}
}
// end of RNulls
}
Returns an enumeration that iterates over provided array.
/*
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
*
* Copyright 1997-2007 Sun Microsystems, Inc. All rights reserved.
*
* The contents of this file are subject to the terms of either the GNU
* General Public License Version 2 only ("GPL") or the Common
* Development and Distribution License("CDDL") (collectively, the
* "License"). You may not use this file except in compliance with the
* License. You can obtain a copy of the License at
* http://www.netbeans.org/cddl-gplv2.html
* or nbbuild/licenses/CDDL-GPL-2-CP. See the License for the
* specific language governing permissions and limitations under the
* License. When distributing the software, include this License Header
* Notice in each file and include the License file at
* nbbuild/licenses/CDDL-GPL-2-CP. Sun designates this
* particular file as subject to the "Classpath" exception as provided
* by Sun in the GPL Version 2 section of the License file that
* accompanied this code. If applicable, add the following below the
* License Header, with the fields enclosed by brackets [] replaced by
* your own identifying information:
* "Portions Copyrighted [year] [name of copyright owner]"
*
* Contributor(s):
*
* The Original Software is NetBeans. The Initial Developer of the Original
* Software is Sun Microsystems, Inc. Portions Copyright 1997-2006 Sun
* Microsystems, Inc. All Rights Reserved.
*
* If you wish your version of this file to be governed by only the CDDL
* or only the GPL Version 2, indicate your decision by adding
* "[Contributor] elects to include this software in this distribution
* under the [CDDL or GPL Version 2] license." If you do not indicate a
* single choice of license, a recipient has the option to distribute
* your version of this file under either the CDDL, the GPL Version 2 or
* to extend the choice of license to its licensees as provided above.
* However, if you add GPL Version 2 code and therefore, elected the GPL
* Version 2 license, then the option applies only if the new code is
* made subject to such option by the copyright holder.
*/
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Enumeration;
import java.util.HashSet;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Set;
/**
* @since 4.37
* @author Jaroslav Tulach
*/
final class Enumerations extends Object {
/**
* Returns an enumeration that iterates over provided array.
* @param arr the array of object
* @return enumeration of those objects
*/
public static <T> Enumeration<T> array(T... arr) {
return Collections.enumeration(Arrays.asList(arr));
}
/**
* Removes all <code>null</code>s from the input enumeration.
* @param en enumeration that can contain nulls
* @return new enumeration without null values
*/
public static <T> Enumeration<T> removeNulls(Enumeration<T> en) {
return filter(en, new RNulls<T>());
}
/**
* For each element of the input enumeration <code>en</code> asks the
* {@link Processor} to provide a replacement.
* The <code>toAdd</code> argument of the processor is always null.
*
* Example to convert any objects into strings:
* <pre>
* Processor convertToString = new Processor() {
* public Object process(Object obj, Collection alwaysNull) {
* return obj.toString(); // converts to string
* }
* };
* Enumeration strings = Enumerations.convert(elems, convertToString);
* </pre>
*
* @param en enumeration of any objects
* @param processor a callback processor for the elements (its toAdd arguments is always null)
* @return new enumeration where all elements has been processed
*/
public static <T,R> Enumeration<R> convert(Enumeration<? extends T> en, Processor<T,R> processor) {
return new AltEn<T,R>(en, processor);
}
/**
* Filters some elements out from the input enumeration.
* Just make the
* {@link Processor} return <code>null</code>. Please notice the <code>toAdd</code>
* argument of the processor is always <code>null</code>.
*
* Example to remove all objects that are not strings:
* <pre>
* Processor onlyString = new Processor() {
* public Object process(Object obj, Collection alwaysNull) {
* if (obj instanceof String) {
* return obj;
* } else {
* return null;
* }
* }
* };
* Enumeration strings = Enumerations.filter(elems, onlyString);
* </pre>
*
* @param en enumeration of any objects
* @param filter a callback processor for the elements (its toAdd arguments is always null)
* @return new enumeration which does not include non-processed (returned null from processor) elements
* @see NbCollections#checkedEnumerationByFilter
*/
public static <T,R> Enumeration<R> filter(Enumeration<? extends T> en, Processor<T,R> filter) {
return new FilEn<T,R>(en, filter);
}
/**
* Support for breadth-first enumerating.
* Before any element is returned
* for the resulting enumeration it is processed in the {@link Processor} and
* the processor is allowed to modify it and also add additional elements
* at the (current) end of the <q>queue</q> by calling <code>toAdd.add</code>
* or <code>toAdd.addAll</code>. No other methods can be called on the
* provided <code>toAdd</code> collection.
*
* Example of doing breadth-first walk through a tree:
* <pre>
* Processor queueSubnodes = new Processor() {
* public Object process(Object obj, Collection toAdd) {
* Node n = (Node)obj;
* toAdd.addAll (n.getChildrenList());
* return n;
* }
* };
* Enumeration strings = Enumerations.queue(elems, queueSubnodes);
* </pre>
*
* @param en initial content of the resulting enumeration
* @param filter the processor that is called for each element and can
* add and addAll elements to its toAdd Collection argument and
* also change the value to be returned
* @return enumeration with the initial and queued content (it can contain
* <code>null</code> if the filter returned <code>null</code> from its
* {@link Processor#process} method.
*/
public static <T,R> Enumeration<R> queue(Enumeration<? extends T> en, Processor<T,R> filter) {
QEn<T,R> q = new QEn<T,R>(filter);
while (en.hasMoreElements()) {
q.put(en.nextElement());
}
return q;
}
/**
* Processor interface that can filter out objects from the enumeration,
* change them or add aditional objects to the end of the current enumeration.
*/
public static interface Processor<T,R> {
/** @param original the object that is going to be returned from the enumeration right now
* @return a replacement for this object
* @param toAdd can be non-null if one can add new objects at the end of the enumeration
*/
public R process(T original, Collection<T> toAdd);
}
/** Altering enumeration implementation */
private static final class AltEn<T,R> extends Object implements Enumeration<R> {
/** enumeration to filter */
private Enumeration<? extends T> en;
/** map to alter */
private Processor<T,R> process;
/**
* @param en enumeration to filter
*/
public AltEn(Enumeration<? extends T> en, Processor<T,R> process) {
this.en = en;
this.process = process;
}
/** @return true if there is more elements in the enumeration
*/
public boolean hasMoreElements() {
return en.hasMoreElements();
}
/** @return next object in the enumeration
* @exception NoSuchElementException can be thrown if there is no next object
* in the enumeration
*/
public R nextElement() {
return process.process(en.nextElement(), null);
}
}
// end of AltEn
/** QueueEnumeration
*/
private static class QEn<T,R> extends Object implements Enumeration<R> {
/** next object to be returned */
private ListItem<T> next = null;
/** last object in the queue */
private ListItem<T> last = null;
/** processor to use */
private Processor<T,R> processor;
public QEn(Processor<T,R> p) {
this.processor = p;
}
/** Put adds new object to the end of queue.
* @param o the object to add
*/
public void put(T o) {
if (last != null) {
ListItem<T> li = new ListItem<T>(o);
last.next = li;
last = li;
} else {
next = last = new ListItem<T>(o);
}
}
/** Adds array of objects into the queue.
* @param arr array of objects to put into the queue
*/
public void put(Collection<? extends T> arr) {
for (T e : arr) {
put(e);
}
}
/** Is there any next object?
* @return true if there is next object, false otherwise
*/
public boolean hasMoreElements() {
return next != null;
}
/** @return next object in enumeration
* @exception NoSuchElementException if there is no next object
*/
public R nextElement() {
if (next == null) {
throw new NoSuchElementException();
}
T res = next.object;
if ((next = next.next) == null) {
last = null;
}
;
ToAdd<T,R> toAdd = new ToAdd<T,R>(this);
R out = processor.process(res, toAdd);
toAdd.finish();
return out;
}
/** item in linked list of Objects */
private static final class ListItem<T> {
T object;
ListItem<T> next;
/** @param o the object for this item */
ListItem(T o) {
object = o;
}
}
/** Temporary collection that supports only add and addAll operations*/
private static final class ToAdd<T,R> extends Object implements Collection<T> {
private QEn<T,R> q;
public ToAdd(QEn<T,R> q) {
this.q = q;
}
public void finish() {
this.q = null;
}
public boolean add(T o) {
q.put(o);
return true;
}
public boolean addAll(Collection<? extends T> c) {
q.put(c);
return true;
}
private String msg() {
return "Only add and addAll are implemented"; // NOI18N
}
public void clear() {
throw new UnsupportedOperationException(msg());
}
public boolean contains(Object o) {
throw new UnsupportedOperationException(msg());
}
public boolean containsAll(Collection c) {
throw new UnsupportedOperationException(msg());
}
public boolean isEmpty() {
throw new UnsupportedOperationException(msg());
}
public Iterator<T> iterator() {
throw new UnsupportedOperationException(msg());
}
public boolean remove(Object o) {
throw new UnsupportedOperationException(msg());
}
public boolean removeAll(Collection c) {
throw new UnsupportedOperationException(msg());
}
public boolean retainAll(Collection c) {
throw new UnsupportedOperationException(msg());
}
public int size() {
throw new UnsupportedOperationException(msg());
}
public Object[] toArray() {
throw new UnsupportedOperationException(msg());
}
public<X> X[] toArray(X[] a) {
throw new UnsupportedOperationException(msg());
}
}
// end of ToAdd
}
// end of QEn
/** Filtering enumeration */
private static final class FilEn<T,R> extends Object implements Enumeration<R> {
/** marker object stating there is no nexte element prepared */
private static final Object EMPTY = new Object();
/** enumeration to filter */
private Enumeration<? extends T> en;
/** element to be returned next time or {@link #EMPTY} if there is
* no such element prepared */
private R next = empty();
/** the set to use as filter */
private Processor<T,R> filter;
/**
* @param en enumeration to filter
*/
public FilEn(Enumeration<? extends T> en, Processor<T,R> filter) {
this.en = en;
this.filter = filter;
}
/** @return true if there is more elements in the enumeration
*/
public boolean hasMoreElements() {
if (next != empty()) {
// there is a object already prepared
return true;
}
while (en.hasMoreElements()) {
// read next
next = filter.process(en.nextElement(), null);
if (next != null) {
// if the object is accepted
return true;
}
;
}
next = empty();
return false;
}
/** @return next object in the enumeration
* @exception NoSuchElementException can be thrown if there is no next object
* in the enumeration
*/
public R nextElement() {
if ((next == EMPTY) && !hasMoreElements()) {
throw new NoSuchElementException();
}
R res = next;
next = empty();
return res;
}
@SuppressWarnings("unchecked")
private R empty() {
return (R)EMPTY;
}
}
// end of FilEn
/** Returns true from contains if object is not null */
private static class RNulls<T> implements Processor<T,T> {
public T process(T original, Collection<T> toAdd) {
return original;
}
}
// end of RNulls
}
Serializable Enumeration
/*
* JBoss, Home of Professional Open Source
* Copyright 2005, JBoss Inc., and individual contributors as indicated
* by the @authors tag. See the copyright.txt in the distribution for a
* full listing of individual contributors.
*
* This is free software; you can redistribute it and/or modify it
* under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation; either version 2.1 of
* the License, or (at your option) any later version.
*
* This software is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this software; if not, write to the Free
* Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
* 02110-1301 USA, or see the FSF site: http://www.fsf.org.
*/
import java.util.ArrayList;
import java.util.Collection;
import java.util.Enumeration;
import java.util.NoSuchElementException;
/**
* ???
*
* @author ???
* @version $Revision: 2800 $
*/
@SuppressWarnings("unchecked")
public class SerializableEnumeration
extends ArrayList
implements Enumeration
{
/** The serialVersionUID */
private static final long serialVersionUID = 8678951571196067510L;
private int index;
public SerializableEnumeration () {
index = 0;
}
public SerializableEnumeration (Collection c) {
super(c);
index = 0;
}
public SerializableEnumeration (int initialCapacity) {
super(initialCapacity);
index = 0;
}
public boolean hasMoreElements() {
return (index < size());
}
public Object nextElement() throws NoSuchElementException
{
try {
Object nextObj = get(index);
index++;
return nextObj;
}
catch (IndexOutOfBoundsException e) {
throw new NoSuchElementException();
}
}
private void writeObject(java.io.ObjectOutputStream out)
throws java.io.IOException
{
// the only thing to write is the index field
out.defaultWriteObject();
}
private void readObject(java.io.ObjectInputStream in)
throws java.io.IOException, ClassNotFoundException
{
in.defaultReadObject();
}
}
Support for breadth-first enumerating.
/*
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
*
* Copyright 1997-2007 Sun Microsystems, Inc. All rights reserved.
*
* The contents of this file are subject to the terms of either the GNU
* General Public License Version 2 only ("GPL") or the Common
* Development and Distribution License("CDDL") (collectively, the
* "License"). You may not use this file except in compliance with the
* License. You can obtain a copy of the License at
* http://www.netbeans.org/cddl-gplv2.html
* or nbbuild/licenses/CDDL-GPL-2-CP. See the License for the
* specific language governing permissions and limitations under the
* License. When distributing the software, include this License Header
* Notice in each file and include the License file at
* nbbuild/licenses/CDDL-GPL-2-CP. Sun designates this
* particular file as subject to the "Classpath" exception as provided
* by Sun in the GPL Version 2 section of the License file that
* accompanied this code. If applicable, add the following below the
* License Header, with the fields enclosed by brackets [] replaced by
* your own identifying information:
* "Portions Copyrighted [year] [name of copyright owner]"
*
* Contributor(s):
*
* The Original Software is NetBeans. The Initial Developer of the Original
* Software is Sun Microsystems, Inc. Portions Copyright 1997-2006 Sun
* Microsystems, Inc. All Rights Reserved.
*
* If you wish your version of this file to be governed by only the CDDL
* or only the GPL Version 2, indicate your decision by adding
* "[Contributor] elects to include this software in this distribution
* under the [CDDL or GPL Version 2] license." If you do not indicate a
* single choice of license, a recipient has the option to distribute
* your version of this file under either the CDDL, the GPL Version 2 or
* to extend the choice of license to its licensees as provided above.
* However, if you add GPL Version 2 code and therefore, elected the GPL
* Version 2 license, then the option applies only if the new code is
* made subject to such option by the copyright holder.
*/
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Enumeration;
import java.util.HashSet;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Set;
/**
* @since 4.37
* @author Jaroslav Tulach
*/
final class Enumerations extends Object {
/**
* Support for breadth-first enumerating.
* Before any element is returned
* for the resulting enumeration it is processed in the {@link Processor} and
* the processor is allowed to modify it and also add additional elements
* at the (current) end of the <q>queue</q> by calling <code>toAdd.add</code>
* or <code>toAdd.addAll</code>. No other methods can be called on the
* provided <code>toAdd</code> collection.
*
* Example of doing breadth-first walk through a tree:
* <pre>
* Processor queueSubnodes = new Processor() {
* public Object process(Object obj, Collection toAdd) {
* Node n = (Node)obj;
* toAdd.addAll (n.getChildrenList());
* return n;
* }
* };
* Enumeration strings = Enumerations.queue(elems, queueSubnodes);
* </pre>
*
* @param en initial content of the resulting enumeration
* @param filter the processor that is called for each element and can
* add and addAll elements to its toAdd Collection argument and
* also change the value to be returned
* @return enumeration with the initial and queued content (it can contain
* <code>null</code> if the filter returned <code>null</code> from its
* {@link Processor#process} method.
*/
public static <T,R> Enumeration<R> queue(Enumeration<? extends T> en, Processor<T,R> filter) {
QEn<T,R> q = new QEn<T,R>(filter);
while (en.hasMoreElements()) {
q.put(en.nextElement());
}
return q;
}
/**
* Processor interface that can filter out objects from the enumeration,
* change them or add aditional objects to the end of the current enumeration.
*/
public static interface Processor<T,R> {
/** @param original the object that is going to be returned from the enumeration right now
* @return a replacement for this object
* @param toAdd can be non-null if one can add new objects at the end of the enumeration
*/
public R process(T original, Collection<T> toAdd);
}
/** Altering enumeration implementation */
private static final class AltEn<T,R> extends Object implements Enumeration<R> {
/** enumeration to filter */
private Enumeration<? extends T> en;
/** map to alter */
private Processor<T,R> process;
/**
* @param en enumeration to filter
*/
public AltEn(Enumeration<? extends T> en, Processor<T,R> process) {
this.en = en;
this.process = process;
}
/** @return true if there is more elements in the enumeration
*/
public boolean hasMoreElements() {
return en.hasMoreElements();
}
/** @return next object in the enumeration
* @exception NoSuchElementException can be thrown if there is no next object
* in the enumeration
*/
public R nextElement() {
return process.process(en.nextElement(), null);
}
}
// end of AltEn
/** QueueEnumeration
*/
private static class QEn<T,R> extends Object implements Enumeration<R> {
/** next object to be returned */
private ListItem<T> next = null;
/** last object in the queue */
private ListItem<T> last = null;
/** processor to use */
private Processor<T,R> processor;
public QEn(Processor<T,R> p) {
this.processor = p;
}
/** Put adds new object to the end of queue.
* @param o the object to add
*/
public void put(T o) {
if (last != null) {
ListItem<T> li = new ListItem<T>(o);
last.next = li;
last = li;
} else {
next = last = new ListItem<T>(o);
}
}
/** Adds array of objects into the queue.
* @param arr array of objects to put into the queue
*/
public void put(Collection<? extends T> arr) {
for (T e : arr) {
put(e);
}
}
/** Is there any next object?
* @return true if there is next object, false otherwise
*/
public boolean hasMoreElements() {
return next != null;
}
/** @return next object in enumeration
* @exception NoSuchElementException if there is no next object
*/
public R nextElement() {
if (next == null) {
throw new NoSuchElementException();
}
T res = next.object;
if ((next = next.next) == null) {
last = null;
}
;
ToAdd<T,R> toAdd = new ToAdd<T,R>(this);
R out = processor.process(res, toAdd);
toAdd.finish();
return out;
}
/** item in linked list of Objects */
private static final class ListItem<T> {
T object;
ListItem<T> next;
/** @param o the object for this item */
ListItem(T o) {
object = o;
}
}
/** Temporary collection that supports only add and addAll operations*/
private static final class ToAdd<T,R> extends Object implements Collection<T> {
private QEn<T,R> q;
public ToAdd(QEn<T,R> q) {
this.q = q;
}
public void finish() {
this.q = null;
}
public boolean add(T o) {
q.put(o);
return true;
}
public boolean addAll(Collection<? extends T> c) {
q.put(c);
return true;
}
private String msg() {
return "Only add and addAll are implemented"; // NOI18N
}
public void clear() {
throw new UnsupportedOperationException(msg());
}
public boolean contains(Object o) {
throw new UnsupportedOperationException(msg());
}
public boolean containsAll(Collection c) {
throw new UnsupportedOperationException(msg());
}
public boolean isEmpty() {
throw new UnsupportedOperationException(msg());
}
public Iterator<T> iterator() {
throw new UnsupportedOperationException(msg());
}
public boolean remove(Object o) {
throw new UnsupportedOperationException(msg());
}
public boolean removeAll(Collection c) {
throw new UnsupportedOperationException(msg());
}
public boolean retainAll(Collection c) {
throw new UnsupportedOperationException(msg());
}
public int size() {
throw new UnsupportedOperationException(msg());
}
public Object[] toArray() {
throw new UnsupportedOperationException(msg());
}
public<X> X[] toArray(X[] a) {
throw new UnsupportedOperationException(msg());
}
}
// end of ToAdd
}
// end of QEn
/** Filtering enumeration */
private static final class FilEn<T,R> extends Object implements Enumeration<R> {
/** marker object stating there is no nexte element prepared */
private static final Object EMPTY = new Object();
/** enumeration to filter */
private Enumeration<? extends T> en;
/** element to be returned next time or {@link #EMPTY} if there is
* no such element prepared */
private R next = empty();
/** the set to use as filter */
private Processor<T,R> filter;
/**
* @param en enumeration to filter
*/
public FilEn(Enumeration<? extends T> en, Processor<T,R> filter) {
this.en = en;
this.filter = filter;
}
/** @return true if there is more elements in the enumeration
*/
public boolean hasMoreElements() {
if (next != empty()) {
// there is a object already prepared
return true;
}
while (en.hasMoreElements()) {
// read next
next = filter.process(en.nextElement(), null);
if (next != null) {
// if the object is accepted
return true;
}
;
}
next = empty();
return false;
}
/** @return next object in the enumeration
* @exception NoSuchElementException can be thrown if there is no next object
* in the enumeration
*/
public R nextElement() {
if ((next == EMPTY) && !hasMoreElements()) {
throw new NoSuchElementException();
}
R res = next;
next = empty();
return res;
}
@SuppressWarnings("unchecked")
private R empty() {
return (R)EMPTY;
}
}
// end of FilEn
/** Returns true from contains if object is not null */
private static class RNulls<T> implements Processor<T,T> {
public T process(T original, Collection<T> toAdd) {
return original;
}
}
// end of RNulls
}
The Enumeration Interface
The Enumeration interface defines a way to traverse all the members of a collection of objects.
The hasMoreElements() method checks to see if there are more elements and returns a boolean.
If there are more elements, nextElement() will return the next element as an Object.
If there are no more elements when nextElement() is called, the runtime NoSuchElementException will be thrown.
import java.util.Enumeration;
import java.util.Vector;
public class MainClass {
public static void main(String args[]) throws Exception {
Vector v = new Vector();
v.add("a");
v.add("b");
v.add("c");
Enumeration e = v.elements();
while (e.hasMoreElements()) {
Object o = e.nextElement();
System.out.println(o);
}
}
}
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The SequenceInputStream Class
import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.InputStreamReader;
import java.io.SequenceInputStream;
import java.util.Enumeration;
import java.util.Vector;
public class MainClass {
public static void main(String args[]) throws Exception {
Vector v = new Vector(3);
v.add(new FileInputStream("/a/b"));
v.add(new FileInputStream("yourfile.bar"));
v.add(new FileInputStream("/yourfile.txt"));
Enumeration e = v.elements();
SequenceInputStream sis = new SequenceInputStream(e);
InputStreamReader isr = new InputStreamReader(sis);
BufferedReader br = new BufferedReader(isr);
String line;
while ((line = br.readLine()) != null) {
System.out.println(line);
}
br.close();
}
}
Where do we get the enumeration from?
Vector, Stack: elements()
Dictionary, Hashtable, Properties: elements(), keys()
import java.util.Collection;
import java.util.Collections;
import java.util.Enumeration;
import java.util.Vector;
public class MainClass {
public static void main(String args[]) throws Exception {
Vector v = new Vector();
v.add("a");
v.add("b");
v.add("c");
Collection col = v;
Enumeration e = Collections.enumeration(col);
for (; e.hasMoreElements();) {
Object o = e.nextElement();
System.out.println(o);
}
}
}
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