如何正确使用ActionListener？

Question

I am trying to make a "simple tetras" game as a beginning coder. As the code shown below, the white block can move by pressing arrow keys while fails to do ( y = y + 10 ) within the Timer. My guess is that the ActionListener is placed in the wrong position. All I want to do is to be able to move the block left and right as it descends.

Here's my code:

import java.awt.event.*;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;

public class Experiment extends JFrame {
    int x = 100;
    int y = 100;
    ASD exp = new ASD();

    public Experiment() {
        add(exp);
        exp.setFocusable(true);
    }

    public class ASD extends JPanel {
        public ASD() {
            addKeyListener(new KeyAdapter() {
                public void keyPressed(KeyEvent e) {
                    switch (e.getKeyCode()) {
                        //case KeyEvent.VK_DOWN: y += 10;break;
                        //case KeyEvent.VK_UP: y -= 10; break;
                        case KeyEvent.VK_LEFT:
                            x -= 10;
                            break;
                        case KeyEvent.VK_RIGHT:
                            x += 10;
                            break;
                    }
                    repaint();
                }
            });
        }

        public void paintComponent(Graphics g) {
            super.paintComponent(g);
            setBackground(Color.BLACK);

            g.setColor(Color.WHITE);
            g.fillRect(x, y, 30, 30);
        }

        public class Movement extends JPanel implements ActionListener {
            Timer tm = new Timer(5, this);

            public void actionPerformed(ActionEvent e) {
                y = y + 10;
                repaint();
            }
        }
    }

    public static void main(String[] args) {
        Experiment frame = new Experiment();
        frame.setTitle("ASD");
        frame.setSize(600, 400);
        frame.setLocationRelativeTo(null);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }
}

Answer 1

The main problems with the code were that

1. The timer needs to be started with the call tm.start()
2. After the block "falls", it needs to be repainted.

Here's a working example of the class ASD

   public class ASD extends JPanel implements ActionListener {

        private Timer tm;

        public ASD() {
            addKeyListener(new KeyAdapter() {
                public void keyPressed(KeyEvent e) {
                    switch (e.getKeyCode()) {
                        //case KeyEvent.VK_DOWN: y += 10;break;
                        //case KeyEvent.VK_UP: y -= 10; break;
                        case KeyEvent.VK_LEFT:
                            x -= 10;
                            break;
                        case KeyEvent.VK_RIGHT:
                            x += 10;
                            break;
                    }
                    repaint();
                }
            });

            tm = new Timer(200, this);
            tm.setRepeats(true);
            tm.start();
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            y = y + 10;
            repaint();
        }

        public void paintComponent(Graphics g) {
            super.paintComponent(g);
            setBackground(Color.BLACK);

            g.setColor(Color.WHITE);
            g.fillRect(x, y, 30, 30);
        }
    }