Swing Hacks

Don’t Block the GUI #92

Chapter 12, Miscellany

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463

HACK

To Block or Not to Block

The demo application is shown in Figure 12-7.

class NonBlockingLoadAction extends AbstractAction implements Runnable {

// note that this doesn't offer a means of being interrupted

// so it refuses second launch instead

public void actionPerformed (ActionEvent e) {

if (loaderThread != null)

return;

loaderThread = new Thread ((Runnable) this);

loaderThread.start( );

}

public void run( ) {

loadURL(true);

loaderThread = null;

}

}

}

Figure 12-7. Blocking and not blocking AWT event dispatch by loading a URL into a

JTextArea

Example 12-8. Demonstration of both blocking and not blocking the AWT event-dispatch

thread during lengthy actions (continued)

464

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Chapter 12, Miscellany

#92 Don’t Block the GUI

HACK

After launching the application, try loading the same address with the block-

ing and non-blocking Load buttons. In the blocking version, you should see

that you can’t open the

JMenu

or reposition the caret in the

JTextField

. If

you’ve already filled the

JTextArea

, you’ll find that the scrollbar is unrespon-

sive while you’re blocking. Drag a window over the demo and then bring the

demo to the foreground—on some operating systems, the area previously

obscured by the window won’t repaint.

Of course, none of this happens when you ...