更改子类中的 jbutton 操作

Question

I'm trying to change button action in a subclass because the form is pretty much exactly the except one asks for an ID. What I i tried doing was making a ActionListener object and instantiating it to an object of an anonymous class like so:

class ParentClass extends JPanel{
    JButton button;
    ActionListener buttonAction;

    ParentClass{
        button = new JButton("Parent Action");
        buttonAction = new ActionListener(){
            @Override
            public void actionPerformed(ActionEvent e) {
                System.out.println("The button was clicked by the parent class");
            }
        };
        button.add(buttonAction);
        add(button);
    }
}

    class ChildClass extends ParentClass{
        JButton button;
        ActionListener buttonAction;

        ChildClass{
            super();
            buttonAction = new ActionListener(){
                @Override
                public void actionPerformed(ActionEvent e) {
                    System.out.println("The button was clicked by the child class");
                }
            };
        }
    }


public static void main(String[] args){
    JFrame frame = new JFrame;
    frame.add(new ChildClass());
    frame.setSize(600, 500);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setVisible(true);

}

I was trying to use this method but the actionPerformed of buttonAction is never called. How can I make the button action different for the parent class and the subclass?

Answer 1

You can let parent class implement ActionListener , then use button.addActionListener(this) in order to add the action to button. Then in the subclass @Override actionPerformed method:

class ParentClass extends JPanel implements ActionListener
{
   ParentClass()
   {
       JButton button = new JButton("something");
       button.addActionListener(this);
       add(button);
    }

    @Override
    public void actionPerformed(ActionEvent event)
    {
        System.out.println("I am the parent.");
    }
}

class SubClass extends ParentClass
{
    SubClass()
    {
       super();//initialize button
    }

     @Override
     public void actionPerformed(ActionEvent event)
     {
         System.out.println("I am the child.");
     }
}

Another way is to add the ActionListener and inside it, only call a method. Something like buttonPressed . Then in subclass @Override buttonPressed method.

A complete example:

public class Test extends JFrame {
    public Test() {
        super("test");
        setDefaultCloseOperation(EXIT_ON_CLOSE);

        setLayout(new GridLayout(2, 1));
        add(new ParentPanel());
        add(new ChildPanel());
        pack();
        setLocationByPlatform(true);
    }

    private class ParentPanel extends JPanel implements ActionListener {
        public ParentPanel() {
            super(new BorderLayout());

            JButton button = new JButton("My Class:" + getClass());
            button.addActionListener(this);
            add(button);
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            System.out.println("Parent");

        }
    }

    private class ChildPanel extends ParentPanel {
        public ChildPanel() {
            super();
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            System.out.println("Child");
        }
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> new Test().setVisible(true));
    }
}

Answer 2

I the method I posted works. The issue is if you don't remove and add the button to the subclass it doesn't change the action that will run

    class ParentClass extends JPanel{
        JButton button;
        ActionListener buttonAction;

        ParentClass{
            button = new JButton("Parent Action");
            buttonAction = new ActionListener(){
                @Override
                public void actionPerformed(ActionEvent e) {
                    System.out.println("The button was clicked by the parent class");
                }
            };
            button.add(buttonAction);
            add(button);
        }
    }

So in the subclass what you would do is this:

    class ChildClass extends ParentClass{
        JButton button;
        ActionListener buttonAction;

        ChildClass{
            super();
            buttonAction = new ActionListener(){
                @Override
                public void actionPerformed(ActionEvent e) {
                    System.out.println("The button was clicked by the child class");
                }
            };
            button.removeActionListener(button.getActionListeners()[0]);
            button.addActionListener(buttonAction);
        }
    }

I, however, do not know why but would like an explanation as to why buttonAction had to be re-registered.