java - 在 Java 中检测按键

Question

我正在制作一个屏幕上有两个球的游戏。一个是电脑控制的，它自己移动，另一个是你用左右键控制的。

public class StartingPoint extends Applet implements Runnable, KeyListener
{

    int x = 356;
    int y = 74;
    double dx = 5;
    double dy = 6;
    int radius = 20;
    //private Image i;
    //private Graphics doubleG;

    int x2 = 0;
    int y2 = 0;
    double dx2 = 0;
    double dy2 = 0;
    int radius2 = 20;

    boolean left = false;
    boolean right = false;


    @Override
    public void init()
    {
        setSize(800, 600);
        setVisible(true);
        setFocusable(true);
        System.out.println("Game Started!");
        System.out.println("init");
    }

    @Override
    public void start()
    {
        Thread thread = new Thread(this);
        thread.start();
        System.out.println("start");
    }

    @Override
    public void run() 
    {
        System.out.println("run");

        while (true)
        {
            x += dx;
            y += dy;

            repaint(); //Goes to update method

            if (x + dx > this.getWidth() -radius -1)
            {
                x = this.getWidth() - radius - 1;
                dx = - dx;
            }

            else if (x + dx < 0 + radius)
            {
                x = 0 + radius;
                dx = -dx;
            }

            else
            {
                x += dx;
            }

            if (y + dy > this.getHeight() -radius -1)
            {
                y = this.getHeight() - radius - 1;
                dy = - dy;
            }

            else if (y + dy < 0 + radius)
            {
                y = 0 + radius;
                dy = -dy;
            }

            else
            {
                y += dy;
            }

            System.out.println("New stuffs");

            x2 += dx2;
            y2 += dy2;

            repaint(); //Goes to update method

            if (x2 + dx2 > this.getWidth() -radius2 -1)
            {
                x2 = this.getWidth() - radius2 - 1;
                dx2 = - dx2;
            }

            else if (x2 + dx2 < 0 + radius2)
            {
                x2 = 0 + radius2;
                dx2 = -dx2;
            }

            else
            {
                x2 += dx2;
            }

            if (y2 + dy2 > this.getHeight() -radius2 -1)
            {
                y2 = this.getHeight() - radius2 - 1;
                dy2 = - dy2;
            }

            else if (y2 + dy2 < 0 + radius2)
            {
                y2 = 0 + radius2;
                dy2 = -dy2;
            }

            else
            {
                y += dy;
            }



            try
            {
                Thread.sleep(17);
            }

            catch (InterruptedException e)
            {
                e.printStackTrace();



            }
        }
    }   

    public void keyPressed(KeyEvent e) 
    {
        System.out.println("KeyPressed");

        switch(e.getKeyCode())
        {
            case KeyEvent.VK_LEFT:
                moveLeftPressedCode();

                System.out.println("VK LEFT");
                break;
            case KeyEvent.VK_RIGHT:
                moveRightPressedCode();
                System.out.println("VK RIGHT");

                break;
        }
    }

    public void keyReleased(KeyEvent e2) 
    {
        System.out.println("KeyReleased");

        switch(e2.getKeyCode())
        {
            case KeyEvent.VK_LEFT:
                moveLeftReleasedCode();
                break;
            case KeyEvent.VK_RIGHT:
                moveRightReleasedCode();
                break;
        }
    }

    public void moveLeftPressedCode()
    {
        left = true;

        System.out.println("");
    }

    public void moveLeftReleasedCode()
    {
        left = false;
    }

    public void moveRightPressedCode()
    {
        right = true;
    }

    public void moveRightReleasedCode()
    {
        right = false;
    }

    public void keyEventLeft()
    {
        if(dx2  >= -7)
        {
            while (left = true)
            {
                dx2 = - 7;
            }
        }       
    }


    public void keyEventRight()
    {
        if(dx2 <= 7)
        {
            while (right = true)
            {
                 //nothing yet
            }
        }
    }

    @Override
    public void stop()
    {

    }

    @Override
    public void destroy()
    {

    }

    @Override
    public void paint(Graphics g)
    {
        g.setColor(Color.BLACK);
        g.fillOval(x - radius, y - radius, radius * 2, radius * 2);
        g.setColor(Color.GREEN);
        g.fillOval(x2 - radius2, y2 - radius2, radius2 * 2, radius2 * 2);
    }

    @Override
    public void keyTyped(KeyEvent arg0) {
        // TODO Auto-generated method stub

    }
}

我遇到的问题是，当我按下左键（或右键）时，该方法不会被调用，因此没有检测到按键。我该如何解决这个问题，或者我需要添加什么才能让游戏检测到我的按键？-谢谢。