<Swing Dev> BasicButtonListener surprising behaviour

[Jean-Rémi Desjardins]

Hi,

I came across this some time ago while working on a project using JDK 6. I
found the behaviour odd and looked at the source code for JDK 7 and was able
find the code that was responsible for the odd behaviour.

Of course, it may well be intended behaviour, but to me it was surprising.

I have looked at the most recent release of the JDK 7 source code, and the
behaviour is still as it was.

I call your attention to the mousePressed(MouseEvent e) function present at
line 213 of BasicButtonListener (javax.swing.plaf.basic) :

public void mousePressed(MouseEvent e) {
       if (SwingUtilities.isLeftMouseButton(e) ) {
          AbstractButton b = (AbstractButton) e.getSource();

          if(b.contains(e.getX(), e.getY())) {
              long multiClickThreshhold = b.getMultiClickThreshhold();
              long lastTime = lastPressedTimestamp;
              long currentTime = lastPressedTimestamp = e.getWhen();
              if (lastTime != -1 && currentTime - lastTime <
multiClickThreshhold) {
                  shouldDiscardRelease = true;
                  return;
              }

             ButtonModel model = b.getModel();
             if (!model.isEnabled()) {
                // Disabled buttons ignore all input...
                return;
             }
             if (!model.isArmed()) {
                // button not armed, should be
                model.setArmed(true);
             }
             model.setPressed(true);
             if(!b.hasFocus() && b.isRequestFocusEnabled()) {
                b.requestFocus();
             }
          }
       }
    }

This behaviour seems odd to me because if one sets the threshold to 0.6
seconds for instance, and the user clicks every 0.5 seconds for
whatever length of time, no mouse clicked event while be generated and
application code while never get notified of any mouse click event. The
behaviour I expected from setting the threshold in the JButton class was
that the second click from the user would generate an event. Indeed, this
seems like it would be the generally desired behaviours and appears to be
the documented behaviour :

Copied from the JDK 7 API documentation :

Sets the amount of time (in milliseconds) required between mouse press
events for the button to generate the corresponding action events. After the
initial mouse press occurs (and action event generated) any subsequent mouse
press events which occur on intervals less than the threshhold will be
ignored and no corresponding action event generated. By default the
threshhold is 0, which means that for each mouse press, an action event will
be fired, no matter how quickly the mouse clicks occur. In buttons where
this behavior is not desirable (for example, the "OK" button in a dialog),
this threshhold should be set to an appropriate positive value.

Could someone let me know if I am missing something or if this is expected
behaviour and why.

Jean-Remi Desjardins

n.b. The code to deliver the behaviour I expect would be something like this
(but I haven't bothered compiling this so no promises) :

public void mousePressed(MouseEvent e) {
       if (SwingUtilities.isLeftMouseButton(e) ) {
          AbstractButton b = (AbstractButton) e.getSource();

          if(b.contains(e.getX(), e.getY())) {
              long multiClickThreshhold = b.getMultiClickThreshhold();
              long lastTime = lastPressedTimestamp;
              long currentTime = e.getWhen();
              if (lastTime != -1 && currentTime - lastTime <
multiClickThreshhold) {
                  shouldDiscardRelease = true;
                  return;
              }
              else {
                  lastPressedTimestamp = currentTime;
              }

             ButtonModel model = b.getModel();
             if (!model.isEnabled()) {
                // Disabled buttons ignore all input...
                return;
             }
             if (!model.isArmed()) {
                // button not armed, should be
                model.setArmed(true);
             }
             model.setPressed(true);
             if(!b.hasFocus() && b.isRequestFocusEnabled()) {
                b.requestFocus();
             }
          }
       }
    }
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