LRUCacheEnumerator.java

/*******************************************************************************
 * Copyright (c) 2000, 2004 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials 
 * are made available under the terms of the Common Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/cpl-v10.html
 * 
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.rubypeople.rdt.internal.core.buffer;

import java.util.Enumeration;

/**
 * The <code>LRUCacheEnumerator</code> returns its elements in the order they
 * are found in the <code>LRUCache</code>, with the most recent elements
 * first.
 * 
 * Once the enumerator is created, elements which are later added to the cache
 * are not returned by the enumerator. However, elements returned from the
 * enumerator could have been closed by the cache.
 */
public class LRUCacheEnumerator implements Enumeration {

    /**
     * Current element;
     */
    protected LRUEnumeratorElement fElementQueue;

    public static class LRUEnumeratorElement {

        /**
         * Value returned by <code>nextElement()</code>;
         */
        public Object fValue;

        /**
         * Next element
         */
        public LRUEnumeratorElement fNext;

        /**
         * Constructor
         */
        public LRUEnumeratorElement(Object value) {
            fValue = value;
        }
    }

    /**
     * Creates a CacheEnumerator on the list of
     * <code>LRUEnumeratorElements</code>.
     */
    public LRUCacheEnumerator(LRUEnumeratorElement firstElement) {
        fElementQueue = firstElement;
    }

    /**
     * Returns true if more elements exist.
     */
    public boolean hasMoreElements() {
        return fElementQueue != null;
    }

    /**
     * Returns the next element.
     */
    public Object nextElement() {
        Object temp = fElementQueue.fValue;
        fElementQueue = fElementQueue.fNext;
        return temp;
    }
}