/*
 *  Copyright 2003-2004 The Apache Software Foundation
 *
 *  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.apache.commons.collections.collection;

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

import org.apache.commons.collections.Unmodifiable;
import org.apache.commons.collections.iterators.UnmodifiableIterator;

/**
 * Decorates another <code>Collection</code> to ensure it can't be altered.
 * <p>
 * This class is Serializable from Commons Collections 3.1.
 *
 * @since Commons Collections 3.0
 * @version $Revision: 155406 $ $Date: 2005-02-26 12:55:26 +0000 (Sat, 26 Feb 2005) $
 * 
 * @author Stephen Colebourne
 */
public final class UnmodifiableCollection
        extends AbstractSerializableCollectionDecorator
        implements Unmodifiable {

    /** Serialization version */
    private static final long serialVersionUID = -239892006883819945L;

    /**
     * Factory method to create an unmodifiable collection.
     * <p>
     * If the collection passed in is already unmodifiable, it is returned.
     * 
     * @param coll  the collection to decorate, must not be null
     * @return an unmodifiable collection
     * @throws IllegalArgumentException if collection is null
     */
    public static Collection decorate(Collection coll) {
        if (coll instanceof Unmodifiable) {
            return coll;
        }
        return new UnmodifiableCollection(coll);
    }
    
    //-----------------------------------------------------------------------
    /**
     * Constructor that wraps (not copies).
     * 
     * @param coll  the collection to decorate, must not be null
     * @throws IllegalArgumentException if collection is null
     */
    private UnmodifiableCollection(Collection coll) {
        super(coll);
    }

    //-----------------------------------------------------------------------
    public Iterator iterator() {
        return UnmodifiableIterator.decorate(getCollection().iterator());
    }

    public boolean add(Object object) {
        throw new UnsupportedOperationException();
    }

    public boolean addAll(Collection coll) {
        throw new UnsupportedOperationException();
    }

    public void clear() {
        throw new UnsupportedOperationException();
    }

    public boolean remove(Object object) {
        throw new UnsupportedOperationException();
    }

    public boolean removeAll(Collection coll) {
        throw new UnsupportedOperationException();
    }

    public boolean retainAll(Collection coll) {
        throw new UnsupportedOperationException();
    }

}