如何将ActionEvent添加到JButton，以便在单击它时将触发事件？

Question

I want to be able to add the ActionListener to the JButton but cannot seem to get it to work properly.

I have tried to add the ActionListeneer and also the ActionEvent and neither seems to fire the ActionPerformed method.

I did not one curious aspect was the the compiler made me take off the @Override keyword since the interface is used to create a variable and not implemented.

Does this make a difference? I am certain that you can do it this way but I think I am just a bit off the mark.

Code:

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import javax.swing.JButton;
import javax.swing.JFrame;

public class testInterfaces2 {
    static ActionListener m;
    static ActionEvent me;

    testInterfaces2() {
    }

    public void actionPerformed(ActionEvent e) {
        System.out.println("Mouse Clicked");
    }

    public static void main(String[] args) {
         JFrame f = new JFrame("Test");

         f.addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent e) {
               System.exit(0);
            }
         });

         JButton pButton = new JButton("Print");
         pButton.addActionListener(m);
         //pButton.addActionListener(m.actionPerformed(me));

         f.add("Center", pButton);
         f.pack();
         f.setVisible(true);
    }
}

Answer 1

It should be like this and remove ActionListener and ActionEvent variables that is not needed.

public class testInterfaces2 implements ActionListener{

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

    ...
    JButton pButton = new JButton("Print");
    pButton.addActionListener(this); 
}

1. @Override doesn't do any thing extra other than compile time checking of the overridden method.

2. In simple term, You need a class that implements ActionListener and obviously implements actionPerformed() method. Simply create a object of that class and pass in addActionListener() method.

Answer 2

I did not one curious aspect was the the compiler made me take off the @Override keyword since the interface is used to create a variable and not implemented.

This should have highlighted your first problem, your testInterfaces2 class can't override actionPerformed as it's not defined in any part of the parent class or it's parents. This is because testInterfaces2 doesn't implement ActionListener directly or indirectly (via inheritance).

Your second problem is m is null , you've never initialised it

Take a closer look at How to write ActionListeners for more details

Answer 3

I think it's best to define a new ActionListener for each button. Like this

JButton pButton = new JButton();

pButton.addActionListener(new ActionListener() {

        @Override
        public void actionPerformed(ActionEvent e) {
            //throw new UnsupportedOperationException("Not supported yet.");
            System.exit(0);
        }
    });