Commons Collections example source code file (ListOrderedSet.java)

This example Commons Collections source code file (ListOrderedSet.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Commons Collections tags/keywords

arraylist, collection, hashset, illegalargumentexception, illegalargumentexception, iterator, list, list, listorderedset, listorderedset, object, object, orderedsetiterator, set, util

The Commons Collections ListOrderedSet.java source code

/*
 *  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.set;

import java.util.ArrayList;
import java.util.Collection;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Set;

import org.apache.commons.collections.iterators.AbstractIteratorDecorator;
import org.apache.commons.collections.list.UnmodifiableList;

/**
 * Decorates another <code>Set to ensure that the order of addition
 * is retained and used by the iterator.
 * <p>
 * If an object is added to the set for a second time, it will remain in the
 * original position in the iteration.
 * The order can be observed from the set via the iterator or toArray methods.
 * <p>
 * The ListOrderedSet also has various useful direct methods. These include many
 * from <code>List, such as get(int), remove(int)
 * and <code>indexOf(int). An unmodifiable List view of 
 * the set can be obtained via <code>asList().
 * <p>
 * This class cannot implement the <code>List interface directly as
 * various interface methods (notably equals/hashCode) are incompatable with a set.
 * <p>
 * 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 Stephen Colebourne
 * @author Henning P. Schmiedehausen
 */
public class ListOrderedSet extends AbstractSerializableSetDecorator implements Set {

    /** Serialization version */
    private static final long serialVersionUID = -228664372470420141L;

    /** Internal list to hold the sequence of objects */
    protected final List setOrder;

    /**
     * Factory method to create an ordered set specifying the list and set to use.
     * <p>
     * The list and set must both be empty.
     * 
     * @param set  the set to decorate, must be empty and not null
     * @param list  the list to decorate, must be empty and not null
     * @throws IllegalArgumentException if set or list is null
     * @throws IllegalArgumentException if either the set or list is not empty
     * @since Commons Collections 3.1
     */
    public static ListOrderedSet decorate(Set set, List list) {
        if (set == null) {
            throw new IllegalArgumentException("Set must not be null");
        }
        if (list == null) {
            throw new IllegalArgumentException("List must not be null");
        }
        if (set.size() > 0 || list.size() > 0) {
            throw new IllegalArgumentException("Set and List must be empty");
        }
        return new ListOrderedSet(set, list);
    }

    /**
     * Factory method to create an ordered set.
     * <p>
     * An <code>ArrayList is used to retain order.
     * 
     * @param set  the set to decorate, must not be null
     * @throws IllegalArgumentException if set is null
     */
    public static ListOrderedSet decorate(Set set) {
        return new ListOrderedSet(set);
    }

    /**
     * Factory method to create an ordered set using the supplied list to retain order.
     * <p>
     * A <code>HashSet is used for the set behaviour.
     * <p>
     * NOTE: If the list contains duplicates, the duplicates are removed,
     * altering the specified list.
     * 
     * @param list  the list to decorate, must not be null
     * @throws IllegalArgumentException if list is null
     */
    public static ListOrderedSet decorate(List list) {
        if (list == null) {
            throw new IllegalArgumentException("List must not be null");
        }
        Set set = new HashSet(list);
        list.retainAll(set);
        
        return new ListOrderedSet(set, list);
    }

    //-----------------------------------------------------------------------
    /**
     * Constructs a new empty <code>ListOrderedSet using
     * a <code>HashSet and an ArrayList internally.
     * 
     * @since Commons Collections 3.1
     */
    public ListOrderedSet() {
        super(new HashSet());
        setOrder = new ArrayList();
    }

    /**
     * Constructor that wraps (not copies).
     * 
     * @param set  the set to decorate, must not be null
     * @throws IllegalArgumentException if set is null
     */
    protected ListOrderedSet(Set set) {
        super(set);
        setOrder = new ArrayList(set);
    }

    /**
     * Constructor that wraps (not copies) the Set and specifies the list to use.
     * <p>
     * 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 ListOrderedSet(Set set, List list) {
        super(set);
        if (list == null) {
            throw new IllegalArgumentException("List must not be null");
        }
        setOrder = list;
    }

    //-----------------------------------------------------------------------
    /**
     * Gets an unmodifiable view of the order of the Set.
     * 
     * @return an unmodifiable list view
     */
    public List asList() {
        return UnmodifiableList.decorate(setOrder);
    }

    //-----------------------------------------------------------------------
    public void clear() {
        collection.clear();
        setOrder.clear();
    }

    public Iterator iterator() {
        return new OrderedSetIterator(setOrder.iterator(), collection);
    }

    public boolean add(Object object) {
        if (collection.contains(object)) {
            // re-adding doesn't change order
            return collection.add(object);
        } else {
            // first add, so add to both set and list
            boolean result = collection.add(object);
            setOrder.add(object);
            return result;
        }
    }

    public boolean addAll(Collection coll) {
        boolean result = false;
        for (Iterator it = coll.iterator(); it.hasNext();) {
            Object object = it.next();
            result = result | add(object);
        }
        return result;
    }

    public boolean remove(Object object) {
        boolean result = collection.remove(object);
        setOrder.remove(object);
        return result;
    }

    public boolean removeAll(Collection coll) {
        boolean result = false;
        for (Iterator it = coll.iterator(); it.hasNext();) {
            Object object = it.next();
            result = result | remove(object);
        }
        return result;
    }

    public boolean retainAll(Collection coll) {
        boolean result = collection.retainAll(coll);
        if (result == false) {
            return false;
        } else if (collection.size() == 0) {
            setOrder.clear();
        } else {
            for (Iterator it = setOrder.iterator(); it.hasNext();) {
                Object object = it.next();
                if (collection.contains(object) == false) {
                    it.remove();
                }
            }
        }
        return result;
    }

    public Object[] toArray() {
        return setOrder.toArray();
    }

    public Object[] toArray(Object a[]) {
        return setOrder.toArray(a);
    }

    //-----------------------------------------------------------------------
    public Object get(int index) {
        return setOrder.get(index);
    }

    public int indexOf(Object object) {
        return setOrder.indexOf(object);
    }

    public void add(int index, Object object) {
        if (contains(object) == false) {
            collection.add(object);
            setOrder.add(index, object);
        }
    }

    public boolean addAll(int index, Collection coll) {
        boolean changed = false;
        for (Iterator it = coll.iterator(); it.hasNext();) {
            Object object = it.next();
            if (contains(object) == false) {
                collection.add(object);
                setOrder.add(index, object);
                index++;
                changed = true;
            }
        }
        return changed;
    }

    public Object remove(int index) {
        Object obj = setOrder.remove(index);
        remove(obj);
        return obj;
    }

    /**
     * Uses the underlying List's toString so that order is achieved. 
     * This means that the decorated Set's toString is not used, so 
     * any custom toStrings will be ignored. 
     */
    // Fortunately List.toString and Set.toString look the same
    public String toString() {
        return setOrder.toString();
    }

    //-----------------------------------------------------------------------
    /**
     * Internal iterator handle remove.
     */
    static class OrderedSetIterator extends AbstractIteratorDecorator {
        
        /** Object we iterate on */
        protected final Collection set;
        /** Last object retrieved */
        protected Object last;

        private OrderedSetIterator(Iterator iterator, Collection set) {
            super(iterator);
            this.set = set;
        }

        public Object next() {
            last = iterator.next();
            return last;
        }

        public void remove() {
            set.remove(last);
            iterator.remove();
            last = null;
        }
    }

}