package com.bbn.openmap.util;import javax.swing.SwingUtilities;/** * This is the 3rd version of SwingWorker (also known as SwingWorker * 3), an abstract class that you subclass to perform GUI-related work * in a dedicated thread. For instructions on using this class, see: *  * http://java.sun.com/docs/books/tutorial/uiswing/misc/threads.html *  * Note that the API changed slightly in the 3rd version: You must now * invoke start() on the SwingWorker after creating it. */public abstract class SwingWorker {    private Object value; // see getValue(), setValue()    /**     * Class to maintain reference to current worker thread under     * separate synchronization control.     */    private static class ThreadVar {        private Thread thread;        ThreadVar(Thread t) {            thread = t;        }        synchronized Thread get() {            return thread;        }        synchronized void clear() {            thread = null;        }    }    private ThreadVar threadVar;    /**     * Get the value produced by the worker thread, or null if it     * hasn't been constructed yet.     */    protected synchronized Object getValue() {        return value;    }    /**     * Set the value produced by worker thread     */    private synchronized void setValue(Object x) {        value = x;    }    /**     * Compute the value to be returned by the <code>get</code>     * method.     */    public abstract Object construct();    /**     * Called on the event dispatching thread (not on the worker     * thread) after the <code>construct</code> method has returned.     */    public void finished() {}    /**     * A new method that interrupts the worker thread. Call this     * method to force the worker to stop what it's doing.     */    public void interrupt() {        Thread t = threadVar.get();        if (t != null) {            t.interrupt();        }        threadVar.clear();    }    /**     * Return the value created by the <code>construct</code>     * method. Returns null if either the constructing thread or the     * current thread was interrupted before a value was produced.     *      * @return the value created by the <code>construct</code>     *         method     */    public Object get() {        while (true) {            Thread t = threadVar.get();            if (t == null) {                return getValue();            }            try {                t.join();            } catch (InterruptedException e) {                Thread.currentThread().interrupt(); // propagate                return null;            }        }    }    /**     * Start a thread that will call the <code>construct</code>     * method and then exit.     */    public SwingWorker() {        final Runnable doFinished = new Runnable() {            public void run() {                finished();            }        };        Runnable doConstruct = new Runnable() {            public void run() {                try {                    setValue(construct());                } finally {                    threadVar.clear();                }                SwingUtilities.invokeLater(doFinished);            }        };        Thread t = new Thread(doConstruct);        threadVar = new ThreadVar(t);    }    /**     * Start the worker thread.     */    public void start() {        Thread t = threadVar.get();        if (t != null) {            t.start();        }    }    /**     * For compatibility with old versions of SwingWorker, calls     * start().     */    public void execute() {        start();    }}