java线程在运行多个线程时不会中断

Question

My project run on java swing there are 2 button (start/stop) for counting.

When I click start button. There is one thread running (Thread-0) ,then click stop button "Thread-0" disappear but when I click start button many times. there are many threads such as Thread-5, Thread-6, .. Thread-10 are running.

Problem : If click start and then stop counting is ok. but click start many times it's incorrect counting.

start button

private void btnStartActionPerformed(java.awt.event.ActionEvent evt) {         
    start();
    btnStart.setEnabled(false);
    btnStop.setEnabled(true);
}   

stop button

private void btnStopActionPerformed(java.awt.event.ActionEvent evt) {            
    isEnable = false;
    btnStop.setEnabled(false);
    btnStart.setEnabled(true);
}    

start() method :

isEnable = true;
Thread refreshPlan = new Thread() {  
    @Override
    public void run() {
        while(isEnable) {
            try {
                sleep(CYCLE_TIME * 1000);
                PLAN += 1;
                planValue.setText(String.valueOf(PLAN));
            } catch (InterruptedException ex) {
                //ignore
            }
        }
    };
    };
    refreshPlan.start();

Can I run only single thread when click many times in start button ? any suggestion? thanks.

sorry for my bad english.

Answer 1

There are four significant problems here:

• Unless isEnable is declared as a volatile variable, there's no guarantee that a write from one thread will be seen in another thread
• Likewise your access to the PLAN counter (which is badly named - please follow Java naming conventions) is unsafe. You may wish to consider using AtomicInteger for this.
• You're making changes to the UI from your extra thread. You can't do that - in Swing (and most UIs) all access to UI components has to be done on the thread responsible for that UI. See the Swing concurrency tutorial for more details.
• Because you only check isEnabled one per second, it would be possible to stop and start multiple threads in the meantime... leading to several threads being active at once. This could interfere with your counting.

You might find it's better to use a javax.swing.Timer which fires once a second, and just checks whether or not it's meant to do anything. That way everything can be on the UI thread.

Answer 2

start method is instantiating new Thread() that's why every time u click it, it brings new thread into life.

declare Thread refreshPlan class variable then in start method put all the code in this check

if(refreshPlan == null || !refreshPlan.isAlive()){
//ur existing code to instantiate new thread.
}