Question

I am trying to flash the background colour in a textfield. My timer setup is as follows:

 Flash flash = new Flash();                      //set up timer
 tmr = new javax.swing.Timer(1000, new Flash());
 tmr.addActionListener(flash);
 tmr.setInitialDelay(0);
 tmr.setRepeats(true);
 tmr.start();                 

My actionListener is as follows:

 static class Flash implements ActionListener
 {
    public void actionPerformed(ActionEvent evt)
    {
        if (flasher)
        {
            SpreademPanel.historyPnl.NameTxt.setBackground(Color.white);
        }
        else
        {
            SpreademPanel.historyPnl.NameTxt.setBackground(Color.pink);
        }
        flasher = !flasher;
    } //actionPerformed
} //Flash

Now, when I put this in debug and follow the action, the program does repeatedly step through flash and toggle between the two alternatives. But onscreen, only the first toggle
occurs. After that, no action, although flash is still functioning.

What is wrong here?

Thanks in advance for any help.

Answer 1

There are a couple of problems here.

The first obvious thing is that you appear to be using mutable statics. This is a really bad idea and indicates (and causes!) confusion. In this particular case, one of the problems caused is that the flasher static is shared.

Flash flash = new Flash();                      //set up timer
tmr = new javax.swing.Timer(1000, new Flash());
tmr.addActionListener(flash);

We are adding two Flash actions. Ordinarily this would be bad, but just produce an undetectable “bug”. The colour would be set twice.

Bring these two things together, and we have two actions without a break that perform the same toggle. Two toggles. The state does not change (although there are repaint, property change events, etc.).

So, don’t use mutable statics, and keep the code clean.