IsEnabled not working when a function is triggered in Java applet

Question

I want a button ("closeButton") to grey out when the function "openExplanations" run. But it is not working.

Gives error Cannot invoke "javax.swing.JButton.setEnabled(boolean)" because "this.closeButton" is null


//the UI
private void initUI() {

hintArea = new JDialog(this);

buttonsPanel = new JPanel();
buttonsPanel.setAlignmentX(0.0f);

JButton closeButton = new JButton(" Close Hint ");
        closeButton.setActionCommand("closeHint");
        closeButton.setVisible(true);
        closeButton.addActionListener(this);
        closeButton.setFocusable(false);
        closeButton.setIcon(createImageIcon("images/constraint/close.gif"));
        buttonsPanel.add(closeButton, BorderLayout.WEST);

hintArea.add(buttonsPanel, BorderLayout.CENTER);
}


private void openExplanation(){
        closeButton.setEnabled(false);
    }

And you are using (or learning) applets because .... ? Applets were deprecated a long time ago. Web browsers no longer support them. Java (9 onwards) is progressively removing support. Writing new applet code (or learning how to do it) is nugatory. — Stephen C, Jun 07 '23 at 23:10
Coz I'm working on a legacy code originally written in 2002. It's research work, so got to stick to the interface. @StephenC — Vedant Bahel, Jun 08 '23 at 02:58
@StephenC [Everything old is new again!](https://www.webswing.org/docs/23.1/configure/applet.html) — Elliott Frisch, Jun 08 '23 at 15:46

score 0 · Answer 1 · answered Jun 07 '23 at 22:39

0

This

JButton closeButton = new JButton(" Close Hint ");

creates a variable shadow. Remove the type declaration. And use this.

this.closeButton = new JButton(" Close Hint ");

answered Jun 07 '23 at 22:39

Elliott Frisch

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Thanks, that worked. I also want to do this for another button. I tried implementing the same thing but that didn't work. This is the code for the other button: openExplanationPanel = new JPanel(); openExplanationPanel.setAlignmentX(0.0f); JButton openExplanationButton = new JButton( isLevel1HintExplanation ? Content.getLevel1Question() : Content.getLevel1QuestionAgain()); – Vedant Bahel Jun 08 '23 at 02:56
Why are you creating another panel? `buttonsPanel.add(openExplanationButton, BorderLayout.EAST);` should do it. Maybe. – Elliott Frisch Jun 08 '23 at 03:13
Cool. It could make it work. Thanks a lot! – Vedant Bahel Jun 08 '23 at 03:31

score 0 · Answer 2 · answered Jun 07 '23 at 22:48

Access to variable issue

By declaring closeButton variable outside of initUI you now make it possible to access this variable from the openExplanation() method.

Code:

// Declare JButton closeButton variable here
private JButton closeButton;

private void initUI() {

  hintArea = new JDialog(this);

  buttonsPanel = new JPanel();
  buttonsPanel.setAlignmentX(0.0 f);

  closeButton = new JButton(" Close Hint ");
  closeButton.setActionCommand("closeHint");
  closeButton.setVisible(true);
  closeButton.addActionListener(this);
  closeButton.setFocusable(false);
  closeButton.setIcon(createImageIcon("images/constraint/close.gif"));
  buttonsPanel.add(closeButton, BorderLayout.WEST);

  hintArea.add(buttonsPanel, BorderLayout.CENTER);
}

private void openExplanation() {
  closeButton.setEnabled(false);
}

IsEnabled not working when a function is triggered in Java applet

2 Answers2

Access to variable issue