我正在尝试编写一个 Java 应用程序，它在屏幕上绘制多个球，这些球会从框架的边缘反弹。我可以成功抽到一个球。但是，当我添加第二个球时，它会覆盖我绘制的初始球。代码是:

import java.awt.*;
import javax.swing.*;
import java.util.ArrayList;
import java.util.List;

public class Ball extends JPanel implements Runnable {

    List<Ball> balls = new ArrayList<Ball>();   
Color color;
int diameter;
long delay;
private int x;
private int y;
private int vx;
private int vy;

public Ball(String ballcolor, int xvelocity, int yvelocity) {
    if(ballcolor == "red") {
        color = Color.red;
    }
    else if(ballcolor == "blue") {
        color = Color.blue;
    }
    else if(ballcolor == "black") {
        color = Color.black;
    }
    else if(ballcolor == "cyan") {
        color = Color.cyan;
    }
    else if(ballcolor == "darkGray") {
        color = Color.darkGray;
    }
    else if(ballcolor == "gray") {
        color = Color.gray;
    }
    else if(ballcolor == "green") {
        color = Color.green;
    }
    else if(ballcolor == "yellow") {
        color = Color.yellow;
    }
    else if(ballcolor == "lightGray") {
        color = Color.lightGray;
    }
    else if(ballcolor == "magenta") {
        color = Color.magenta;
    }
    else if(ballcolor == "orange") {
        color = Color.orange;
    }
    else if(ballcolor == "pink") {
        color = Color.pink;
    }
    else if(ballcolor == "white") {     
        color = Color.white;
    }
    diameter = 30;
    delay = 40;
    x = 1;
    y = 1;
    vx = xvelocity;
    vy = yvelocity;
}

protected void paintComponent(Graphics g) {
    super.paintComponent(g);
    Graphics2D g2 = (Graphics2D)g;
    g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
    g.setColor(color);
    g.fillOval(x,y,30,30); //adds color to circle
    g.setColor(Color.black);
    g2.drawOval(x,y,30,30); //draws circle
}

public void run() {
    while(isVisible()) {
        try {
            Thread.sleep(delay);
        } catch(InterruptedException e) {
            System.out.println("interrupted");
        }
        move();
        repaint();
    }
}

public void move() {
    if(x + vx < 0 || x + diameter + vx > getWidth()) {
        vx *= -1;
    }
    if(y + vy < 0 || y + diameter + vy > getHeight()) {
        vy *= -1;
    }
    x += vx;
    y += vy;
}

private void start() {
    while(!isVisible()) {
        try {
            Thread.sleep(25);
        } catch(InterruptedException e) {
            System.exit(1);
        }
    }
    Thread thread = new Thread(this);
    thread.setPriority(Thread.NORM_PRIORITY);
    thread.start();
}

public static void main(String[] args) {
    Ball ball1 = new Ball("red",3,2);
    Ball ball2 = new Ball("blue",6,2);
    JFrame f = new JFrame();
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    f.getContentPane().add(ball1);
    f.getContentPane().add(ball2);
    f.setSize(400,400);
    f.setLocation(200,200);
    f.setVisible(true);
    new Thread(ball1).start();
    new Thread(ball2).start();
}
}

我想创建一个球列表，然后循环绘制每个球，但我仍然无法将两个球添加到内容 Pane 。

感谢您的帮助。

最佳答案

根据您当前的方法...

• 我能看到的主要问题是您将两个不透明组件放在彼此之上...实际上您可能会发现您正在绕过其中一个组件...
• 您应该使用 null 布局管理器，否则它将接管并按照它认为合适的方式布局您的球。
• 您需要确保控制球形 Pane 的大小和位置。这意味着您已经接管了布局管理器的角色...
• 您需要随机化球的速度和位置，以减少它们从同一位置开始并移动到同一位置的机会...
• 仅在 EDT 的上下文中更新 Ball。
• 您实际上并不需要 X/Y 值，您可以使用面板。

.

public class AnimatedBalls {

    public static void main(String[] args) {
        new AnimatedBalls();
    }

    public AnimatedBalls() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException ex) {
                } catch (InstantiationException ex) {
                } catch (IllegalAccessException ex) {
                } catch (UnsupportedLookAndFeelException ex) {
                }

                JFrame frame = new JFrame();
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(new Balls());
                frame.setSize(400, 400);
                frame.setVisible(true);
            }
        });
    }

    public class Balls extends JPanel {

        public Balls() {
            setLayout(null);
            // Randomize the speed and direction...
            add(new Ball("red", 10 - (int) Math.round((Math.random() * 20)), 10 - (int) Math.round((Math.random() * 20))));
            add(new Ball("blue", 10 - (int) Math.round((Math.random() * 20)), 10 - (int) Math.round((Math.random() * 20))));
        }
    }

    public class Ball extends JPanel implements Runnable {

        Color color;
        int diameter;
        long delay;
        private int vx;
        private int vy;

        public Ball(String ballcolor, int xvelocity, int yvelocity) {
            if (ballcolor == "red") {
                color = Color.red;
            } else if (ballcolor == "blue") {
                color = Color.blue;
            } else if (ballcolor == "black") {
                color = Color.black;
            } else if (ballcolor == "cyan") {
                color = Color.cyan;
            } else if (ballcolor == "darkGray") {
                color = Color.darkGray;
            } else if (ballcolor == "gray") {
                color = Color.gray;
            } else if (ballcolor == "green") {
                color = Color.green;
            } else if (ballcolor == "yellow") {
                color = Color.yellow;
            } else if (ballcolor == "lightGray") {
                color = Color.lightGray;
            } else if (ballcolor == "magenta") {
                color = Color.magenta;
            } else if (ballcolor == "orange") {
                color = Color.orange;
            } else if (ballcolor == "pink") {
                color = Color.pink;
            } else if (ballcolor == "white") {
                color = Color.white;
            }
            diameter = 30;
            delay = 100;

            vx = xvelocity;
            vy = yvelocity;

            new Thread(this).start();

        }

        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2 = (Graphics2D) g;

            int x = getX();
            int y = getY();

            g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
            g.setColor(color);
            g.fillOval(0, 0, 30, 30); //adds color to circle
            g.setColor(Color.black);
            g2.drawOval(0, 0, 30, 30); //draws circle
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(30, 30);
        }

        public void run() {

            try {
                // Randamize the location...
                SwingUtilities.invokeAndWait(new Runnable() {
                    @Override
                    public void run() {
                        int x = (int) (Math.round(Math.random() * getParent().getWidth()));
                        int y = (int) (Math.round(Math.random() * getParent().getHeight()));

                        setLocation(x, y);
                    }
                });
            } catch (InterruptedException exp) {
                exp.printStackTrace();
            } catch (InvocationTargetException exp) {
                exp.printStackTrace();
            }

            while (isVisible()) {
                try {
                    Thread.sleep(delay);
                } catch (InterruptedException e) {
                    System.out.println("interrupted");
                }

                try {
                    SwingUtilities.invokeAndWait(new Runnable() {
                        @Override
                        public void run() {
                            move();
                            repaint();
                        }
                    });
                } catch (InterruptedException exp) {
                    exp.printStackTrace();
                } catch (InvocationTargetException exp) {
                    exp.printStackTrace();
                }
            }
        }

        public void move() {

            int x = getX();
            int y = getY();

            if (x + vx < 0 || x + diameter + vx > getParent().getWidth()) {
                vx *= -1;
            }
            if (y + vy < 0 || y + diameter + vy > getParent().getHeight()) {
                vy *= -1;
            }
            x += vx;
            y += vy;

            // Update the size and location...
            setSize(getPreferredSize());
            setLocation(x, y);

        }
    }
}

这种方法的“主要”问题是每个 Ball 都有自己的 Thread。当你增加球的数量时，这将很快消耗你的系统资源......

不同的方法

从 Hovercraft 开始，您最好为球创建一个容器，其中球不是组件，而是球的“虚拟”概念，包含足够的信息，可以将它们弹开墙壁……

public class SimpleBalls {

    public static void main(String[] args) {
        new SimpleBalls();
    }

    public SimpleBalls() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException ex) {
                } catch (InstantiationException ex) {
                } catch (IllegalAccessException ex) {
                } catch (UnsupportedLookAndFeelException ex) {
                }

                JFrame frame = new JFrame("Spot");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                Balls balls = new Balls();
                frame.add(balls);
                frame.setSize(400, 400);
                frame.setVisible(true);

                new Thread(new BounceEngine(balls)).start();

            }
        });
    }

    public static int random(int maxRange) {
        return (int) Math.round((Math.random() * maxRange));
    }

    public class Balls extends JPanel {

        private List<Ball> ballsUp;

        public Balls() {
            ballsUp = new ArrayList<Ball>(25);

            for (int index = 0; index < 10 + random(90); index++) {
                ballsUp.add(new Ball(new Color(random(255), random(255), random(255))));
            }
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();
            g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
            for (Ball ball : ballsUp) {
                ball.paint(g2d);
            }
            g2d.dispose();
        }

        public List<Ball> getBalls() {
            return ballsUp;
        }
    }

    public class BounceEngine implements Runnable {

        private Balls parent;

        public BounceEngine(Balls parent) {
            this.parent = parent;
        }

        @Override
        public void run() {

            int width = getParent().getWidth();
            int height = getParent().getHeight();

            // Randomize the starting position...
            for (Ball ball : getParent().getBalls()) {
                int x = random(width);
                int y = random(height);

                Dimension size = ball.getSize();

                if (x + size.width > width) {
                    x = width - size.width;
                }
                if (y + size.height > height) {
                    y = height - size.height;
                }

                ball.setLocation(new Point(x, y));

            }

            while (getParent().isVisible()) {

                // Repaint the balls pen...
                SwingUtilities.invokeLater(new Runnable() {
                    @Override
                    public void run() {
                        getParent().repaint();
                    }
                });

                // This is a little dangrous, as it's possible
                // for a repaint to occur while we're updating...
                for (Ball ball : getParent().getBalls()) {
                    move(ball);
                }

                // Some small delay...
                try {
                    Thread.sleep(100);
                } catch (InterruptedException ex) {
                }

            }

        }

        public Balls getParent() {
            return parent;
        }

        public void move(Ball ball) {

            Point p = ball.getLocation();
            Point speed = ball.getSpeed();
            Dimension size = ball.getSize();

            int vx = speed.x;
            int vy = speed.y;

            int x = p.x;
            int y = p.y;

            if (x + vx < 0 || x + size.width + vx > getParent().getWidth()) {
                vx *= -1;
            }
            if (y + vy < 0 || y + size.height + vy > getParent().getHeight()) {
                vy *= -1;
            }
            x += vx;
            y += vy;

            ball.setSpeed(new Point(vx, vy));
            ball.setLocation(new Point(x, y));

        }
    }

    public class Ball {

        private Color color;
        private Point location;
        private Dimension size;
        private Point speed;

        public Ball(Color color) {

            setColor(color);

            speed = new Point(10 - random(20), 10 - random(20));
            size = new Dimension(30, 30);

        }

        public Dimension getSize() {
            return size;
        }

        public void setColor(Color color) {
            this.color = color;
        }

        public void setLocation(Point location) {
            this.location = location;
        }

        public Color getColor() {
            return color;
        }

        public Point getLocation() {
            return location;
        }

        public Point getSpeed() {
            return speed;
        }

        public void setSpeed(Point speed) {
            this.speed = speed;
        }

        protected void paint(Graphics2D g2d) {

            Point p = getLocation();
            if (p != null) {
                g2d.setColor(getColor());
                Dimension size = getSize();
                g2d.fillOval(p.x, p.y, size.width, size.height);
            }

        }
    }
}

因为这是由单线程驱动的，所以它的可扩展性要高得多。

您还可以查看 the images are not loading这是一个类似的问题；)

关于Java 弹跳球，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/13022754/