jdk/src/share/classes/javax/swing/text/SegmentCache.java

/*
 * Copyright 2001 Sun Microsystems, Inc.  All Rights Reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Sun designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Sun in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
 * CA 95054 USA or visit www.sun.com if you need additional information or
 * have any questions.
 */
package javax.swing.text;

import java.util.ArrayList;
import java.util.List;

/**
 * SegmentCache caches <code>Segment</code>s to avoid continually creating
 * and destroying of <code>Segment</code>s. A common use of this class would
 * be:
 * <pre>
 *   Segment segment = segmentCache.getSegment();
 *   // do something with segment
 *   ...
 *   segmentCache.releaseSegment(segment);
 * </pre>
 *
 */
class SegmentCache {
    /**
     * A global cache.
     */
    private static SegmentCache sharedCache = new SegmentCache();

    /**
     * A list of the currently unused Segments.
     */
    private List segments;


    /**
     * Returns the shared SegmentCache.
     */
    public static SegmentCache getSharedInstance() {
        return sharedCache;
    }

    /**
     * A convenience method to get a Segment from the shared
     * <code>SegmentCache</code>.
     */
    public static Segment getSharedSegment() {
        return getSharedInstance().getSegment();
    }

    /**
     * A convenience method to release a Segment to the shared
     * <code>SegmentCache</code>.
     */
    public static void releaseSharedSegment(Segment segment) {
        getSharedInstance().releaseSegment(segment);
    }



    /**
     * Creates and returns a SegmentCache.
     */
    public SegmentCache() {
        segments = new ArrayList(11);
    }

    /**
     * Returns a <code>Segment</code>. When done, the <code>Segment</code>
     * should be recycled by invoking <code>releaseSegment</code>.
     */
    public Segment getSegment() {
        synchronized(this) {
            int size = segments.size();

            if (size > 0) {
                return (Segment)segments.remove(size - 1);
            }
        }
        return new CachedSegment();
    }

    /**
     * Releases a Segment. You should not use a Segment after you release it,
     * and you should NEVER release the same Segment more than once, eg:
     * <pre>
     *   segmentCache.releaseSegment(segment);
     *   segmentCache.releaseSegment(segment);
     * </pre>
     * Will likely result in very bad things happening!
     */
    public void releaseSegment(Segment segment) {
        if (segment instanceof CachedSegment) {
            synchronized(this) {
                segment.array = null;
                segment.count = 0;
                segments.add(segment);
            }
        }
    }


    /**
     * CachedSegment is used as a tagging interface to determine if
     * a Segment can successfully be shared.
     */
    private static class CachedSegment extends Segment {
    }
}