org.openide.util.Enumerations Maven / Gradle / Ivy
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* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
package org.openide.util;
import java.util.ArrayList;
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;
import org.openide.util.Parameters;
/**
* Factory methods for various types of {@link Enumeration}.
* Allows composition of existing enumerations, filtering their contents, and/or modifying them.
* All of this is designed to be done lazily, i.e. elements created on demand.
* @since 4.37
* @author Jaroslav Tulach
* @see NbCollections#checkedEnumerationByFilter
* @see NbCollections#iterable(Enumeration)
*/
public final class Enumerations extends Object {
/** No instances */
private Enumerations() {
}
/**
* An empty enumeration.
* Always returns false from
* empty().hasMoreElements() and throws NoSuchElementException
* from empty().nextElement().
* @return the enumeration
*/
public static final Enumeration empty() {
Collection emptyL = Collections.emptyList();
return Collections.enumeration(emptyL);
}
/**
* Creates an enumeration with one element.
* @param obj the element to be present in the enumeration.
* @return enumeration
*/
public static Enumeration singleton(T obj) {
return Collections.enumeration(Collections.singleton(obj));
}
/**
* Concatenates the content of two enumerations into one.
* Until the
* end of en1 is reached its elements are being served.
* As soon as the en1 has no more elements, the content
* of en2 is being returned.
*
* @param en1 first enumeration
* @param en2 second enumeration
* @return enumeration
*/
public static Enumeration concat(Enumeration en1, Enumeration en2) {
ArrayList> two = new ArrayList>();
two.add(en1);
two.add(en2);
return new SeqEn(Collections.enumeration(two));
}
/**
* Concatenates the content of many enumerations.
* The input value
* is enumeration of Enumeration elements and the result is composed
* all their content. Each of the provided enumeration is fully read
* and their content returned before the next enumeration is asked for
* their elements.
*
* @param enumOfEnums Enumeration of Enumeration elements
* @return enumeration
*/
public static Enumeration concat(Enumeration> enumOfEnums) {
return new SeqEn(enumOfEnums);
}
/**
* 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 Enumeration removeDuplicates(Enumeration en) {
class RDupls implements Processor {
private Set set = new HashSet();
public T process(T o, Collection 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 Enumeration 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 Enumeration removeNulls(Enumeration en) {
return filter(en, new RNulls());
}
/**
* 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 Enumeration convert(Enumeration en, Processor processor) {
return new AltEn(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 Enumeration filter(Enumeration en, Processor filter) {
Parameters.notNull("en", en);
Parameters.notNull("filter", filter);
return new FilEn(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 Enumeration queue(Enumeration en, Processor filter) {
QEn q = new QEn(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 {
/** @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 toAdd);
}
/** Altering enumeration implementation */
private static final class AltEn extends Object implements Enumeration {
/** enumeration to filter */
private Enumeration en;
/** map to alter */
private Processor process;
/**
* @param en enumeration to filter
*/
public AltEn(Enumeration en, Processor 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
/** Sequence of enumerations */
private static final class SeqEn extends Object implements Enumeration {
/** enumeration of Enumerations */
private Enumeration> en;
/** current enumeration */
private Enumeration 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 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> 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();
}
}
}
// end of SeqEn
/** QueueEnumeration
*/
private static class QEn extends Object implements Enumeration {
/** next object to be returned */
private ListItem next = null;
/** last object in the queue */
private ListItem last = null;
/** processor to use */
private Processor processor;
public QEn(Processor 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 li = new ListItem(o);
last.next = li;
last = li;
} else {
next = last = new ListItem(o);
}
}
/** Adds array of objects into the queue.
* @param arr array of objects to put into the queue
*/
public void put(Collection 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 toAdd = new ToAdd(this);
R out = processor.process(res, toAdd);
toAdd.finish();
return out;
}
/** item in linked list of Objects */
private static final class ListItem {
T object;
ListItem 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 extends Object implements Collection {
private QEn q;
public ToAdd(QEn q) {
this.q = q;
}
public void finish() {
this.q = null;
}
public boolean add(T o) {
q.put(o);
return true;
}
public boolean addAll(Collection 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 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[] toArray(X[] a) {
throw new UnsupportedOperationException(msg());
}
}
// end of ToAdd
}
// end of QEn
/** Filtering enumeration */
private static final class FilEn extends Object implements Enumeration {
/** marker object stating there is no nexte element prepared */
private static final Object EMPTY = new Object();
/** enumeration to filter */
private Enumeration 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 filter;
/**
* @param en enumeration to filter
*/
public FilEn(Enumeration en, Processor 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 implements Processor {
public T process(T original, Collection toAdd) {
return original;
}
}
// end of RNulls
}