CODEWITHSUNDEEP
javaswingstack-overflow
Luuk Wuijster
Luuk Wuijster

Reputation: 6878

Java, StackOverflowError when extending a class, or instantiating

Okay, at first, I know why I am getting this error, but just don't how to solve it.

I have a couple classes, a main class, a layout class and a buttonClick class.

The problem is in the buttonClick class: I have some variables in my layout class that I have to use in my buttonClick class.

This is my Layout class:

public class Layout extends JPanel {
    public JButton BTN_werpen;

    public Layout{
        BTN_werpen = new JButton("Werpen");
        BTN_werpen.setBounds(465, 10, 80, 30);
        BTN_werpen.addActionListener(new WerpButton());
        P_velden.add(BTN_werpen);
    }

Of course, this is not the full class, but it's everything you need to know.

The I have my 'WerpButton' actionListner class:

public class WerpButton extends Layout implements ActionListener {
    BTN_werpen.setEnabled(false);
}

Again, this is not everything, but it already fails when I just use the code here. And I know why it fails: that's because when the Layout class gets extended the constructor gets called and it will create a new object, which triggers the WerpButton class what then calls the Layout class, and so on. It basically becomes a loop.

Now, my question is:

How do I solve this problem?

I've tried a lot already, like not extending it but just use Layout layout = new Layout(); And then using layout.BTN_werpen in my code, but that does not work too.

Upvotes: 0

Views: 331

Answers (1)

OneCricketeer
OneCricketeer

Reputation: 191864

public class WerpButton extends Layout

So, you create new WerpButton() essentially called new Layout()

public Layout() {
    ...
    BTN_werpen.addActionListener(new WerpButton());
    ...
}

Which again called new WerpButton... and the loop repeats

Why does an ActionListener have the name anything-"Button"? (unless implemented on the button class itself, of course).

In other words, why does did you implement ActionListener on a Layout?

Did you mean to extend JButton instead of Layout?

public class WerpButton extends JButton implements ActionListener {
    public WerpButton() {
        this.addActionListener(this);
    }

    @Override
    public void onActionPerformed(ActionEvent e) {
        this.setEnabled(false);
    }
}

Besides, this would not have worked if you had a separate class file

public class WerpButton extends Layout implements ActionListener {
    BTN_werpen.setEnabled(false); // 'BTN_werpen' can't be resolved. 
}

You can try doing it the other way - the layout implements the listener. That way you do not need a separate class strictly to handle button events. 

public class Layout extends JPanel implements ActionListener {
    public JButton BTN_werpen;

    public Layout() {
        BTN_werpen = new JButton("Werpen");
        BTN_werpen.setBounds(465, 10, 80, 30);
        BTN_werpen.addActionListener(this);
        P_velden.add(BTN_werpen);
    }

    @Override
    public void onActionPerformed(ActionEvent e) {
        if (e.getSource() == BTN_werpen) {
            // handle click
            BTN_werpen.setEnabled(false);
        }
    }

Upvotes: 2

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