package net.sourceforge.jwap.util;import javax.swing.SwingUtilities;public abstract class SwingWorker {    private Object value; private ThreadVar threadVar;    /**
 * 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);    }    /**
 * 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 the worker thread.
 */    public void start() {        Thread t = threadVar.get();        if (t != null) {            t.start();        }    }    /**
 * 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;        }    }}