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'databene commons' is an open source Java library by Volker Bergmann. It provides extensions to the Java core library by utility classes, abstract concepts and concrete implementations.
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/*
 * Copyright (C) 2004-2015 Volker Bergmann ([email protected]).
 * All rights reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * http://www.apache.org/licenses/LICENSE-2.0
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.databene.commons;

import java.util.Collection;
import java.util.Iterator;
import java.util.Set;

/**
 * {@link Set} implementation that tracks the order in which elements where added
 * and returns them in that order by the iterator() method. 
 * This is useful for all cases in which elements need to be unique
 * but processed in the original order.
 * Created at 28.02.2009 12:26:35
 * @param  the type of the collection's elements
 * @since 0.4.8
 * @author Volker Bergmann
 */

public class OrderedSet implements Set {
	
	private OrderedMap map;
	
    public OrderedSet() {
        map = new OrderedMap();
    }

    public OrderedSet(int initialCapacity) {
        map = new OrderedMap(initialCapacity);
    }

    public OrderedSet(int initialCapacity, float loadFactor) {
        map = new OrderedMap(initialCapacity, loadFactor);
    }

    public OrderedSet(Collection source) {
        map = new OrderedMap(source.size());
        addAll(source);
    }
    
    // Set interface implementation ------------------------------------------------------------------------------------

    @Override
	public boolean add(E item) {
	    return (map.put(item, item) == null);
    }

    @Override
	public boolean addAll(Collection source) {
    	boolean changed = false;
    	for (E item : source)
        	changed |= add(item);
    	return changed; 
    }

    @Override
	public void clear() {
	    map.clear();
    }

    @Override
	public boolean contains(Object item) {
	    return map.containsKey(item);
    }

    @Override
	public boolean containsAll(Collection items) {
	    for (Object o : items)
	    	if (!map.containsKey(o))
	    		return false;
	    return true;
    }

    @Override
	public boolean isEmpty() {
	    return map.isEmpty();
    }

    @Override
	public Iterator iterator() {
	    return map.keySet().iterator();
    }

    @Override
	public boolean remove(Object item) {
	    return (map.remove(item) != null);
    }

    @Override
	public boolean removeAll(Collection items) {
    	boolean changed = false;
	    for (Object item : items)
	    	changed |= remove(item);
	    return changed;
    }

    @Override
	public boolean retainAll(Collection items) {
    	boolean changed = false;
	    for (E item : map.keySet())
	    	if (!items.contains(item)) {
	    		map.remove(item);
	    		changed = true;
	    	}
	    return changed;
    }

    @Override
	public int size() {
	    return map.size();
    }

    @Override
	public Object[] toArray() {
	    return map.keySet().toArray();
    }

    @Override
	public  T[] toArray(T[] array) {
	    return map.keySet().toArray(array);
    }
    
    // List interface --------------------------------------------------------------------------------------------------

    public E get(int index) {
        return map.valueAt(index);
    }
    
    // java.lang.Object overrides --------------------------------------------------------------------------------------

	@Override
    public int hashCode() {
	    return map.hashCode();
    }

	@SuppressWarnings("rawtypes")
    @Override
    public boolean equals(Object obj) {
	    if (this == obj)
		    return true;
	    if (obj == null || getClass() != obj.getClass())
		    return false;
	    return (this.map.equals(((OrderedSet) obj).map));
    }

    @Override
    public String toString() {
        return map.toString();
    }
}