Swing Hacks

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Chapter 12, Miscellany

#97 Mirror an Application

HACK

Put all of this together, with the following main( ) method, and then fire up

two copies of your program. The first one will wait for a connection. When

the second one starts, it will send every mouse event over the network to the

first copy, which will then reuse it. If you click on the button in the second

window, you will see the button depress in the first.

public static void main(String[] args) throws Exception {

ApplicationMirrorTest mirror = new ApplicationMirrorTest( );

mirror.start( );

}

Component Problems

Wait...did this work? No, it didn’t. The events still don’t work after being

sent over the network. A little debugging will show that every part of the

reconstituted event works properly except for the

getComponent( ) method,

which returns

null. Why?

The reference to the component doesn’t get sent over the wire because that

would require sending the component itself. That component, of course, is

part of your entire Swing tree, which would also have to be sent over. Pretty

soon you’d be sending a few megabytes through the network for every event.

To avoid this, the developers of Java made the component reference tran-

sient, which means the object will be skipped during serialization. That

makes the component fast, but it presents a problem: how do you know

which component the event goes with?

When you think about it, you wouldn’t