Event Dispatching Thread and invokeLater 's argument
Hello there:
I have a question about the Event Dispatching Thread and SwingUtilities.invokeLater.
Normally, we construct a runnable object to include GUI-update code, and pass this object as an argument to SwingUtilities.invokeLater. By doing so the EDT will take over to take care of the component update (for the thread-safe APIs we don't have to do like this).
Question is, I thought EDT is a single thread, but obviously when we create runnable objects as above, a couple new threads have been generated. So how does invokeLater work on EDT to resolve this mystery?
I hope I've mede myself understood,
Thanks for your answers,
Sway
# 2
bsampieri:
Thx for the reply. However, I need to clarify: Runnable is an interface, I know that. When I say a runnable object, what I meant was to construct an object to implement runnable interface, which creates a new thread.
Very often we do like this:
SwingUtilities.invokeLater(new Runnable(){
public void run(){
...
}
});
Supposed if we write code like above a couple times in an app, several threads will be created. My question was, if this is what's happened, how does EDT, which is a single thread, handle these threads? Does it queue them? Or in another word, how does invokeLater work on EDT?
Thanks,
Sway
# 3
Creating a Runnable does not start a new Thread. Running a Runnable does not start a new Thread either. A Runnable is just a normal object, like any other object, and its run() method is just a normal method, like any other method.
Now, you can start a new thread in which you run your Runnable, but the Runnable itself will not do that:
Runnable job = new Runnable() {
public void run() {
...
}
};
job.run() // the call to run() is made from the current thread. No new thread is started.
new Thread(job).start(); // you start a new thread, that runs the job
# 4
>
> Supposed if we write code like above a couple times
> in an app, several threads will be created. My
> question was, if this is what's happened, how does
> EDT, which is a single thread, handle these threads?
> Does it queue them? Or in another word, how does
> invokeLater work on EDT?
>
Yes, everytime you call invokeLater(), the Runnable will be placed on the event queue. The EDT will run them one by one, in the same order as they were added.
# 5
SwingUtilities.invokeLater(new Runnable(){
public void run(){
...
}
});
...does not create nor start a new thread.
Only...
new Thread(new Runnable(){
public void run(){
...
}
}).start();
...does create and start a new thread. SwingUtilities.invokeXxx() methods do not do this. It simply dumps the Runnable object into a queue and the EDT will get to it eventually and see it's a Runnable and will call the run() method.
