为什么我的代码“Bouncing ball”不起作用？

Question

我正在尝试编写关于弹跳球的代码，但是我仍然沉迷于如何
使弹跳球。该代码似乎是正确的，日食没有错误消息
，但是球还是没有动。任何帮助/提示表示赞赏。

这是我的代码：

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

public class BouncingBallTest extends JFrame {

    private JButton jbtStart = new JButton("Start");
    private JButton jbtStop = new JButton("Stop");
    private Ball canvas = new Ball();

    public BouncingBallTest() {
        JPanel panel = new JPanel(); // Use the panel to group buttons
        panel.add(jbtStart);
        panel.add(jbtStop);

        add(canvas, BorderLayout.CENTER); // Add canvas to centre
        add(panel, BorderLayout.SOUTH); // Add panel to south

        // register listener
        jbtStart.addActionListener(new StartBouncingBallTest());
        jbtStop.addActionListener(new StopBouncingBallTest());

    }

    // the main method
    public static void main(String[] args) {
        JFrame frame = new BouncingBallTest();
        frame.setTitle("Bouncing Ball Test");
        frame.setLocationRelativeTo(null);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(470, 300);
        frame.setVisible(true);
    }

    class StartBouncingBallTest implements ActionListener { // inner class
        @Override
        public void actionPerformed(ActionEvent e) {
            canvas.StartBouncingBallTest();
        }
    }

    class StopBouncingBallTest implements ActionListener { // inner class
        @Override
        public void actionPerformed(ActionEvent e) {
            canvas.StopBouncingBallTest();
        }
    }

    class Ball extends JPanel {
        private int radius = 10;
        private int x;
        private int y;
        private int dx = 3;
        private int dy = 3;

        private Timer timer = new Timer(20, new TimerListener());

        public void StartBouncingBallTest() {
            if (x > 0 && y > 0) {
                x += dx;
                y += dy;
            }

            else if (x == 0) {
                x -= dx;
                y += dy;
            }

            else if (y + (2 * radius) > getHeight()) {
                x += dx;
                y -= dy;
            }

            else if (y == 0) {
                x += dx;
                y -= dy;
            }

            else if (x + (2 * radius) > getWidth()) {
                x -= dx;
                y += dy;
            }
            repaint();

            timer.start();

        }

        public void StopBouncingBallTest() {

            timer.stop();
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            g.setColor(Color.GREEN);
            g.fillOval(x, y, 2 * radius, 2 * radius);

        }
    }

    class TimerListener implements ActionListener {
        @Override
        public void actionPerformed(ActionEvent e) {
            repaint();
        }
    }

}

Answer 1

基本上，什么都没有移动。

每次SwingTimer滴答作响，您要做的就是重新粉刷。

您需要将移动逻辑移至actionPerformed已ActionListener注册的方法Timer

更像…

public void StartBouncingBallTest() {
    timer.start();
}

//...

class TimerListener implements ActionListener {
    @Override
    public void actionPerformed(ActionEvent e) {
        if (x > 0 && y > 0) {
            x += dx;
            y += dy;
        }

        else if (x == 0) {
            x -= dx;
            y += dy;
        }

        else if (y + (2 * radius) > getHeight()) {
            x += dx;
            y -= dy;
        }

        else if (y == 0) {
            x += dx;
            y -= dy;
        }

        else if (x + (2 * radius) > getWidth()) {
            x -= dx;
            y += dy;
        }
        repaint();
    }
}

这样，每次Timer打勾时，您都在相应地更新球的位置…

更新了工作示例

我做了两个更改。我将设置TimerListener为的内部类Ball，从而允许它访问的变量和方法，Ball并修改了您的
运动逻辑，使其可以正常工作

class Ball extends JPanel {

    private int radius = 10;
    private int x;
    private int y;
    private int dx = 3;
    private int dy = 3;

    private Timer timer = new Timer(20, new TimerListener());

    public void StartBouncingBallTest() {

        timer.start();

    }

    public void StopBouncingBallTest() {

        timer.stop();
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.setColor(Color.GREEN);
        g.fillOval(x, y, 2 * radius, 2 * radius);

    }

    class TimerListener implements ActionListener {

        @Override
        public void actionPerformed(ActionEvent e) {

            if (x < 0 || x + (2 * radius) > getWidth()) {
                dx *= -1;
            }
            if (y < 0 || y + (2 * radius) > getHeight()) {
                dy *= -1;
            }

            x += dx;
            y += dy;
            repaint();
        }
    }
}