import javax.swing.SwingUtilities;

/**
 * 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/products/jfc/swingdoc/threads.html
 */

abstract class SwingWorker {
    private Object value;
    private Thread thread;

    /** 
     * 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() {
    }

    /**
     * Return the value created by the <code>construct</code> method.  
     */
    public Object get() {
	while (true) {  // keep trying if we're interrupted
	    Thread t;
	    synchronized (SwingWorker.this) {
		t = thread;
		if (t == null) {
		    return value;
		}
	    }
	    try {
		t.join();
	    }
	    catch (InterruptedException e) {
	    }
	}
    }

    /**
     * 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() {
		synchronized(SwingWorker.this) {
		    value = construct();
		    thread = null;
		}
		SwingUtilities.invokeLater(doFinished);
	    }
	};

	thread = new Thread(doConstruct);
	thread.start();
    }
}