org.apache.commons.collections.list.SetUniqueList Maven / Gradle / Ivy
/*
* 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.apache.commons.collections.list;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;
import java.util.Set;
import org.apache.commons.collections.iterators.AbstractIteratorDecorator;
import org.apache.commons.collections.iterators.AbstractListIteratorDecorator;
import org.apache.commons.collections.set.UnmodifiableSet;
/**
* Decorates a List to ensure that no duplicates are present
* much like a Set.
*
* The List interface makes certain assumptions/requirements.
* This implementation breaks these in certain ways, but this is merely the
* result of rejecting duplicates.
* Each violation is explained in the method, but it should not affect you.
* Bear in mind that Sets require immutable objects to function correctly.
*
* The {@link org.apache.commons.collections.set.ListOrderedSet ListOrderedSet}
* class provides an alternative approach, by wrapping an existing Set and
* retaining insertion order in the iterator.
*
* This class is Serializable from Commons Collections 3.1.
*
* @since Commons Collections 3.0
* @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
*
* @author Matthew Hawthorne
* @author Stephen Colebourne
* @author Tom Dunham
*/
public class SetUniqueList extends AbstractSerializableListDecorator {
/** Serialization version */
private static final long serialVersionUID = 7196982186153478694L;
/**
* Internal Set to maintain uniqueness.
*/
protected final Set set;
/**
* Factory method to create a SetList using the supplied list to retain order.
*
* If the list contains duplicates, these are removed (first indexed one kept).
* A HashSet is used for the set behaviour.
*
* @param list the list to decorate, must not be null
* @throws IllegalArgumentException if list is null
*/
public static SetUniqueList decorate(List list) {
if (list == null) {
throw new IllegalArgumentException("List must not be null");
}
if (list.isEmpty()) {
return new SetUniqueList(list, new HashSet());
} else {
List temp = new ArrayList(list);
list.clear();
SetUniqueList sl = new SetUniqueList(list, new HashSet());
sl.addAll(temp);
return sl;
}
}
//-----------------------------------------------------------------------
/**
* Constructor that wraps (not copies) the List and specifies the set to use.
*
* The set and list must both be correctly initialised to the same elements.
*
* @param set the set to decorate, must not be null
* @param list the list to decorate, must not be null
* @throws IllegalArgumentException if set or list is null
*/
protected SetUniqueList(List list, Set set) {
super(list);
if (set == null) {
throw new IllegalArgumentException("Set must not be null");
}
this.set = set;
}
//-----------------------------------------------------------------------
/**
* Gets an unmodifiable view as a Set.
*
* @return an unmodifiable set view
*/
public Set asSet() {
return UnmodifiableSet.decorate(set);
}
//-----------------------------------------------------------------------
/**
* Adds an element to the list if it is not already present.
*
* (Violation)
* The List interface requires that this method returns
* true always. However this class may return false
* because of the Set behaviour.
*
* @param object the object to add
* @return true if object was added
*/
public boolean add(Object object) {
// gets initial size
final int sizeBefore = size();
// adds element if unique
add(size(), object);
// compares sizes to detect if collection changed
return (sizeBefore != size());
}
/**
* Adds an element to a specific index in the list if it is not already present.
*
* (Violation)
* The List interface makes the assumption that the element is
* always inserted. This may not happen with this implementation.
*
* @param index the index to insert at
* @param object the object to add
*/
public void add(int index, Object object) {
// adds element if it is not contained already
if (set.contains(object) == false) {
super.add(index, object);
set.add(object);
}
}
/**
* Adds an element to the end of the list if it is not already present.
*
* (Violation)
* The List interface makes the assumption that the element is
* always inserted. This may not happen with this implementation.
*
* @param coll the collection to add
*/
public boolean addAll(Collection coll) {
return addAll(size(), coll);
}
/**
* Adds a collection of objects to the end of the list avoiding duplicates.
*
* Only elements that are not already in this list will be added, and
* duplicates from the specified collection will be ignored.
*
* (Violation)
* The List interface makes the assumption that the elements
* are always inserted. This may not happen with this implementation.
*
* @param index the index to insert at
* @param coll the collection to add in iterator order
* @return true if this collection changed
*/
public boolean addAll(int index, Collection coll) {
// gets initial size
final int sizeBefore = size();
// adds all elements
for (final Iterator it = coll.iterator(); it.hasNext();) {
add(it.next());
}
// compares sizes to detect if collection changed
return sizeBefore != size();
}
//-----------------------------------------------------------------------
/**
* Sets the value at the specified index avoiding duplicates.
*
* The object is set into the specified index.
* Afterwards, any previous duplicate is removed
* If the object is not already in the list then a normal set occurs.
* If it is present, then the old version is removed.
*
* @param index the index to insert at
* @param object the object to set
* @return the previous object
*/
public Object set(int index, Object object) {
int pos = indexOf(object);
Object removed = super.set(index, object);
if (pos == -1 || pos == index) {
return removed;
}
// the object is already in the uniq list
// (and it hasn't been swapped with itself)
super.remove(pos); // remove the duplicate by index
set.remove(removed); // remove the item deleted by the set
return removed; // return the item deleted by the set
}
public boolean remove(Object object) {
boolean result = super.remove(object);
set.remove(object);
return result;
}
public Object remove(int index) {
Object result = super.remove(index);
set.remove(result);
return result;
}
public boolean removeAll(Collection coll) {
boolean result = super.removeAll(coll);
set.removeAll(coll);
return result;
}
public boolean retainAll(Collection coll) {
boolean result = super.retainAll(coll);
set.retainAll(coll);
return result;
}
public void clear() {
super.clear();
set.clear();
}
public boolean contains(Object object) {
return set.contains(object);
}
public boolean containsAll(Collection coll) {
return set.containsAll(coll);
}
public Iterator iterator() {
return new SetListIterator(super.iterator(), set);
}
public ListIterator listIterator() {
return new SetListListIterator(super.listIterator(), set);
}
public ListIterator listIterator(int index) {
return new SetListListIterator(super.listIterator(index), set);
}
public List subList(int fromIndex, int toIndex) {
return new SetUniqueList(super.subList(fromIndex, toIndex), set);
}
//-----------------------------------------------------------------------
/**
* Inner class iterator.
*/
static class SetListIterator extends AbstractIteratorDecorator {
protected final Set set;
protected Object last = null;
protected SetListIterator(Iterator it, Set set) {
super(it);
this.set = set;
}
public Object next() {
last = super.next();
return last;
}
public void remove() {
super.remove();
set.remove(last);
last = null;
}
}
/**
* Inner class iterator.
*/
static class SetListListIterator extends AbstractListIteratorDecorator {
protected final Set set;
protected Object last = null;
protected SetListListIterator(ListIterator it, Set set) {
super(it);
this.set = set;
}
public Object next() {
last = super.next();
return last;
}
public Object previous() {
last = super.previous();
return last;
}
public void remove() {
super.remove();
set.remove(last);
last = null;
}
public void add(Object object) {
if (set.contains(object) == false) {
super.add(object);
set.add(object);
}
}
public void set(Object object) {
throw new UnsupportedOperationException("ListIterator does not support set");
}
}
}