Java Tutorial/Collections/Enumeration Interface
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.
<source lang="java">
/**
* * 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;
}
}</source>
Concatenates the content of two enumerations into one.
<source lang="java">
/*
* 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 ofen1is reached its elements are being served. * As soon as theen1has no more elements, the content * ofen2is 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 current == null and
* 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 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 current 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();
}
}
}</source>
Creating Custom Enumerations
<source lang="java">
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());
}
}
}</source>
2 3 5 8 13 21 Invalid type: class java.lang.String
Filters enumeration to contain each of the provided elements just once.
<source lang="java">
/*
* 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 equals and hashCode 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 nulls 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 en asks the
* {@link Processor} to provide a replacement.
* The toAdd argument of the processor is always null.
*
* Example to convert any objects into strings:
*
* Processor convertToString = new Processor() {
* public Object process(Object obj, Collection alwaysNull) {
* return obj.toString(); // converts to string
* }
* };
* Enumeration strings = Enumerations.convert(elems, convertToString);
*
*
* @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 null. Please notice the toAdd
* argument of the processor is always null.
*
* Example to remove all objects that are not strings:
*
* 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);
*
*
* @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 queue
by calling toAdd.add
* or toAdd.addAll. No other methods can be called on the
* provided toAdd collection.
*
* Example of doing breadth-first walk through a tree:
*
* 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);
*
*
* @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
* null if the filter returned null 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
}</source>
Filters some elements out from the input enumeration.
<source lang="java">
/*
* 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 null. Please notice the toAdd
* argument of the processor is always null.
*
* Example to remove all objects that are not strings:
*
* 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);
*
*
* @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 queue
by calling toAdd.add
* or toAdd.addAll. No other methods can be called on the
* provided toAdd collection.
*
* Example of doing breadth-first walk through a tree:
*
* 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);
*
*
* @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
* null if the filter returned null 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
}</source>
For each element of the input enumeration asks the Processor to provide a replacement
<source lang="java">
/*
* 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 en asks the
* {@link Processor} to provide a replacement.
* The toAdd argument of the processor is always null.
*
* Example to convert any objects into strings:
*
* Processor convertToString = new Processor() {
* public Object process(Object obj, Collection alwaysNull) {
* return obj.toString(); // converts to string
* }
* };
* Enumeration strings = Enumerations.convert(elems, convertToString);
*
*
* @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 null. Please notice the toAdd
* argument of the processor is always null.
*
* Example to remove all objects that are not strings:
*
* 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);
*
*
* @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 queue
by calling toAdd.add
* or toAdd.addAll. No other methods can be called on the
* provided toAdd collection.
*
* Example of doing breadth-first walk through a tree:
*
* 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);
*
*
* @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
* null if the filter returned null 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
}</source>
If you prefer a for-loop
<source lang="java">
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);
}
}
}</source>
a b c
Removes all nulls from the input enumeration.
<source lang="java">
/*
* 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 nulls 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 en asks the
* {@link Processor} to provide a replacement.
* The toAdd argument of the processor is always null.
*
* Example to convert any objects into strings:
*
* Processor convertToString = new Processor() {
* public Object process(Object obj, Collection alwaysNull) {
* return obj.toString(); // converts to string
* }
* };
* Enumeration strings = Enumerations.convert(elems, convertToString);
*
*
* @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 null. Please notice the toAdd
* argument of the processor is always null.
*
* Example to remove all objects that are not strings:
*
* 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);
*
*
* @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 queue
by calling toAdd.add
* or toAdd.addAll. No other methods can be called on the
* provided toAdd collection.
*
* Example of doing breadth-first walk through a tree:
*
* 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);
*
*
* @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
* null if the filter returned null 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
}</source>
Returns an enumeration that iterates over provided array.
<source lang="java">
/*
* 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 nulls 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 en asks the
* {@link Processor} to provide a replacement.
* The toAdd argument of the processor is always null.
*
* Example to convert any objects into strings:
*
* Processor convertToString = new Processor() {
* public Object process(Object obj, Collection alwaysNull) {
* return obj.toString(); // converts to string
* }
* };
* Enumeration strings = Enumerations.convert(elems, convertToString);
*
*
* @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 null. Please notice the toAdd
* argument of the processor is always null.
*
* Example to remove all objects that are not strings:
*
* 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);
*
*
* @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 queue
by calling toAdd.add
* or toAdd.addAll. No other methods can be called on the
* provided toAdd collection.
*
* Example of doing breadth-first walk through a tree:
*
* 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);
*
*
* @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
* null if the filter returned null 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
}</source>
Serializable Enumeration
<source lang="java">
/*
* 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();
}
}</source>
Support for breadth-first enumerating.
<source lang="java">
/*
* 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 queue
by calling toAdd.add
* or toAdd.addAll. No other methods can be called on the
* provided toAdd collection.
*
* Example of doing breadth-first walk through a tree:
*
* 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);
*
*
* @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
* null if the filter returned null 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
}</source>
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.
<source lang="java">
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);
}
}
}</source>
a b c
The SequenceInputStream Class
<source lang="java">
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();
}
}</source>
Where do we get the enumeration from?
Vector, Stack: elements()
Dictionary, Hashtable, Properties: elements(), keys()
<source lang="java">
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);
}
}
}</source>
a b c
