How do I access each individual ActionPerformed for buttons?

Question

I want to thank Andrew Thompson for helping me get this far in the code. How do I access each individual button's actionPerformed listener?

The code is supposed to move the "ball" on the screen based on the button you press.

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class Lab2a extends JFrame {

Lab2a(){
    setTitle("Lab 1b - Application #2");
    Lab2Panel p = new Lab2Panel();
    add(p);
}

public static void main(String[] args){

Lab2 frame = new Lab2();
frame.setTitle("Lab2 Application # 1");
frame.setLocationRelativeTo(null);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(600, 400);
frame.setVisible(true);
}

}

class Lab2Panel extends JPanel{
Lab2Button canvas = new Lab2Button();
JPanel panel = new JPanel();

Lab2Panel () {

setLayout(new BorderLayout());

JButton leftButton = new JButton("left");
JButton rightButton = new JButton("right");
JButton upButton = new JButton("up");
JButton downButton = new JButton("down");

panel.add(leftButton);
panel.add(rightButton);
panel.add(upButton);
panel.add(downButton);

this.add(canvas, BorderLayout.CENTER);
this.add(panel, BorderLayout.SOUTH);

leftButton.addActionListener(new Lab2MoveBallListener(canvas));
rightButton.addActionListener(new Lab2MoveBallListener(canvas));
}


}

class Lab2Button extends JPanel {
int radius = 5;
int x = -1;
int y = -1;

protected void paintComponent(Graphics g){
    if (x<0 || y<0) {
        x = getWidth() / 2 - radius;
        y = getHeight() / 2 - radius;
    }
    super.paintComponent(g);
    g.drawOval(x,y, 2 * radius, 2 * radius);

}

    public void moveLeft(){

        x -= 5;
        this.repaint();
    }

    public void moveRight(){

        x += 5;
        this.repaint();
    }

    public void moveUp(){
        y += 5;
        this.repaint();
    }

    public void moveDown(){
        y -= 5;
        this.repaint();
    }


}

class Lab2MoveBallListener implements ActionListener{
    private Lab2Button canvas;

Lab2MoveBallListener(Lab2Button canvas) {
    this.canvas = canvas;
 }

public void actionPerformed(ActionEvent e){
    canvas.moveLeft();
}

}

Answer 1

Since you are using 1 action listener class with 2 buttons you will have to have a way to tell which button was pressed. You can try something like this in the actionPerformed method:

 public void actionPerformed(ActionEvent e) {
    if(e.getActionCommand().matches("left"))
      System.out.print("left button pressed");
    else if(e.getActionCommand().matches("right"))
      System.out.print("right button pressed");
}

another way would be to do this is to create an anonymous class by doing this:

 buttonLeft.addActionListener(new ActionListener(){
      public void actionPerformed(){
        //left button code
      }
    });

  buttonRight.addActionListener(new ActionListener(){
    public void actionPerformed(){
      //right button code
    }
  });

Answer 2

In the ActionListener's actionPerformed(...) method, you can get the text of the button that's been pressed via the ActionEvent's getActionCommand() method.

Just test it to see the results:

public void actionPerformed(ActionEvent e){
    String actionCommand = e.getActionCommand();

    System.out.println("actionCommand is: " + actionCommand);
}

Now you can use this information inside of this method to do more than just write to the standard out, but I'll let you figure out the rest.