为什么我的代码“弹跳球”不行吗 [英] why my code "Bouncing ball" doesn't work?

问题描述

我正在尝试编写一个反弹弹球的代码，但我被困在如何使球弹起来。该代码似乎是正确的，没有错误的消息从日食，但球不动。

I'm trying to write a code a bout a bouncing ball, but i'm stuck in how to make the ball bounced. The code seems correct, no wrong messages from eclipse and yet the ball doesn't move. Any help/hint is appreciate.

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();
        }
    }

}

推荐答案

基本上没有什么是移动球。

Basically, nothing is moving the ball.

每次Swing 计时器你所做的只是重绘。

Each time the Swing Timer ticks, all you do is repaint.

你需要将运动逻辑移动到 actionPerformed c $ c> ActionListener 注册到计时器

You need to move the movement logic to the actionPerformed method of the ActionListener registered to the 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

This way, each time the Timer ticks, you are making update the position of the ball accordingly...

使用实例更新

我进行了两次更改。我使你的 TimerListener 一个内部类 Ball ，它允许它访问<$ c $的变量和方法c> Ball 并修改您的移动逻辑，以使其正常工作

I made two changes. I made your TimerListener an inner class of Ball, which allows it to access the variable and methods of Ball and modified your movement logic so it works

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();
        }
    }
}

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