Application: gvSIG desktop » gvSIG projections

package org.gvsig.proj.swing.impl.history;

import java.util.Collections;

import java.util.Iterator;

import java.util.List;

import java.util.concurrent.CopyOnWriteArrayList;

import org.gvsig.proj.swing.RecentHistory;

/**

 * Stores a collection of objects, removing the oldest objects when the size

 * of the collection grows beyond the allowed {@link #getMaxSize() maxSize}.

 * 

 * This implementation is thread-safe. It is optimized for small collections of

 * objects which are queried more often than modified. The collection is backed 

 * by a CopyOnWriteArrayList instance.

 * 

 * @author Cesar Martinez Izquierdo

 *

 * @param <E>

 */

public class History<E> implements RecentHistory<E> {

        public static final int DEFAULT_MAX_SIZE = 8;

        private final CopyOnWriteArrayList<E> historyArray;

        private final int maxSize;

        public History() {

                this(DEFAULT_MAX_SIZE);

        }

        public History(int maxSize) {

                historyArray = new CopyOnWriteArrayList<E>();

                this.maxSize = maxSize;

        }

        public History(List<E> values, int maxSize) {

                historyArray = new CopyOnWriteArrayList<E>(values);

                this.maxSize = maxSize;

        }

        /* (non-Javadoc)

         * @see org.gvsig.proj.swing.impl.history.IHistory#getMaxSize()

         */

        @Override

        public int getMaxSize() {

                return this.maxSize;

        }

        /* (non-Javadoc)

         * @see org.gvsig.proj.swing.impl.history.IHistory#add(E)

         */

        @Override

        public synchronized boolean add(E element) {

                int pos;

                if ((pos = historyArray.indexOf(element)) != -1) {

                        if (pos==0) {

                                // already in the top of the queue

                                return false;

                        }

                        historyArray.remove(pos);

                }

                if (historyArray.size() == maxSize) {

                        historyArray.remove(maxSize-1);

                }

                historyArray.add(0, element);

                return true;

        }

        @Override

        public int size() {

                return historyArray.size();

        }

        @Override

        public boolean isEmpty() {

                return historyArray.isEmpty();

        }

        @Override

        public boolean contains(Object o) {

                return historyArray.contains(o);

        }

        @Override

        public Iterator<E> iterator() {

                return historyArray.iterator();

        }

        @Override

        public List<E> toList() {

                return Collections.unmodifiableList(historyArray);

        }

}