在Java中使用Swing GUI中的线程

Question

I am using the following codes, to replace a JLabel each 0.5 seconds, with the same sentence but with another dot.

    Runnable r1=new Runnable() {
        @Override
        public void run() {
            while(true){
                try {
                    connectionStatus.setText("Connection Established...");
                    Thread.sleep(500L);
                    connectionStatus.setText("Connection Established.");
                    Thread.sleep(500L);
                    connectionStatus.setText("Connection Established..");
                    Thread.sleep(500L);
                } catch (InterruptedException ex) {

                }
            }
        }
    };
Thread th1=new Thread(r1);
th1.start();

Is this the real purpose from using threads? Does this affect the speed of the program? If the thing that I'm doing is so stupid, is there any other way to do such stupid things?

Answer 1

Is this the real purpose from using threads?

If you want these operations to run in parallel then the answer is yes

is there any other way to do such stupid things?

If you update your label at a fixed intervals then you should probably go for using Timer s instead

On a side note:

• You should avoid using while(true) when doing multithreading, you should either define a stop boolean that you test in the loop or use Thread.interrupted() if you extend the Thread class
• When updating UI elements from non EDT thread, you should use SwingUtilities.invokeLater

Answer 2

Try using a Timer from Swing library instead. It's generally a better idea to use these for GUI-related tasks. This will especially come in handy when you try to use timed events on multiple components as all Timers share the same timer thread.

It also provides a flexible and intuitive programming model based on listeners.

No need to reinvent the wheel.

Timer tutorial

EDIT:

A little followup on the wheel reinvention part. You should also take Andrew Thompson's suggestion into consideration. There are components in Swing that have been designed specifically to indicate progress. It's unnecessary to do it using a label, as you're trying to do. Take a look at JProgressBar . It's going to be simple and it will look more professional.

Answer 3

First one suggestion, rather use something like this:

while(!isStopped) {
  // do some work
}

With your approach you just created infinity loop.

Note: Have look at Java Timer . It's very usefull and efficient.

Answer 4

There are several issues with this code.

1. Swing components should be accessed/updated on the Event Dispatch Thread and are not thread-safe. So starting another Thread to update your JLabel is simply not done. See the 'Concurrency in Swing' tutorial for more information
2. Even if you would call the code above on the EDT, you would not see any updates of the JLabel as the Thread.sleep would block the EDT, and avoiding a repaint.

So the solution is to use the javax.swing.Timer class, which allows to perform operations on the EDT at regular intervals, and does not block the EDT in between. See also the Timer tutorial . As a side effect, using timers avoids the while(true) loop which would never end.

You can find a more complete answer here .

Answer 5

Try this,

1. You will need the above approach if your purpose is parallel processing .

2. You have given while (true) , which will lead to a Infinite loop, you must control it, its better to have a boolean variable to control the nos. of iteration of the while loop.

3. Keep you non-ui thread processing OUT of the Event Dispatcher Thread , else you will make the GUI hang till your thread has finished its run() method. In your case its Infinite, as while (true).

4. If you want to sync the non-ui work and ui work , then you can use Handler or Swing-Worker.

5. Last but not the least, Take a look at TimeTask , see this link

   http://enos.itcollege.ee/~jpoial/docs/tutorial/essential/threads/timer.html