关于键盘监听的问题－在线等。

谢谢楼上的mu_x(阿木) 。我猜也是。只是要如何让Canvas获得焦点？请再帮忙。

一个Frame类add(new Canvas()).
……………………………………………………………………
Canvas c = new Canvas();
frame.getContentPane().add(c);
c.requestFocus(true);

感谢thomas_20(执子之手，与子偕老) 的解答，遗憾的是，问题依然没有解决。我想可能是我的代码中有一些问题吧因此帖出来，望指点。。（Core JAVA II线程一章的代码）
/**
* The frame with canvas and buttons.
*/
class BounceFrame extends JFrame {    /**
     * Constructs the frame with the canvas for showing the
     * bouncing ball and Start and Close buttons
     */
    public BounceFrame() {
        setSize(WIDTH, HEIGHT);
        setTitle("BounceThread");
        setLocation(112, 84);        Container contentPane = this.getContentPane();
        canvas = new BallCanvas();
        contentPane.add(canvas, BorderLayout.CENTER);
canvas.requestFocus();

        JPanel buttonPanel = new JPanel();
        addButton(buttonPanel, "Start", new ActionListener() {
            public void actionPerformed(ActionEvent evt) {
                addBall();
            }
        });
        addButton(buttonPanel, "Close", new ActionListener() {
            public void actionPerformed(ActionEvent evt) {
                System.exit(0);
            }
        });
        contentPane.add(buttonPanel, BorderLayout.SOUTH);

        this.setFocusable(true);
    }    /**
    Adds a button to a container.
    @param c the container
    @param title the button title
    @param listener the action listener for the button
    */
    public void addButton(Container c, String title, ActionListener listener) {
        JButton button = new JButton(title);
        c.add(button);
        button.addActionListener(listener);
    }    /**
    Adds a bouncing ball to the canvas and starts a thread
    to make it bounce
    */
    public void addBall() {
        Ball b = new Ball(canvas);
        canvas.add(b);
        BallThread thread = new BallThread(b);
        thread.start();
    }    private BallCanvas canvas;
    public static final int WIDTH = 800;
    public static final int HEIGHT = 600;}

线程类---------------------------
/**
A thread that animates a bouncing ball.
*/
class BallThread extends Thread {    /**
    Constructs the thread.
    @aBall the ball to bounce
    */
    public BallThread(Ball aBall) {
        b = aBall;
    }    public void run() {
        try {
            while (true) {
                b.move();
                sleep(5);
            }
        } catch (InterruptedException exception) {}
    }    private Ball b;
}

画布类－－－－－－－－－－－－－－－－－－
/**
*The canvas that draws the balls.
*/
class BallCanvas extends JPanel {    public BallCanvas() {
     this.setBackground(new Color(255,255,255));
        addKeyListener(new KeyListener() {            /* （非 Javadoc）
             * @see java.awt.event.KeyListener#keyPressed(java.awt.event.KeyEvent)
             */
            public void keyPressed(KeyEvent e) {
                System.out.println("the keyPressed method is invoked!");
            }            /* （非 Javadoc）
             * @see java.awt.event.KeyListener#keyReleased(java.awt.event.KeyEvent)
             */
            public void keyReleased(KeyEvent e) {}            /* （非 Javadoc）
             * @see java.awt.event.KeyListener#keyTyped(java.awt.event.KeyEvent)
             */
            public void keyTyped(KeyEvent e) {}        });
    }    /**
    Add a ball to the canvas.
    @param b the ball to add
    */
    public void add(Ball b) {
        balls.add(b);
    }    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D) g;
        for (int i = 0; i < balls.size(); i++) {
            Ball b = (Ball) balls.get(i);
            b.draw(g2);
        }
    }    private ArrayList balls = new ArrayList();
    private static int width = 800;
    private static int height = 600;}

运行的时候焦点在JButton上了吧（接着猜^_^），不用JButton试一下。

刚才边帖了三帖，不让继续了。还有一个Ball类。
/**
* A ball that moves and bounces off the edges of a
* component
*/
class Ball {    /**
     * Constructs a ball in the upper left corner
     * @c the component in which the ball bounces
     */
    public Ball(Component c) {
        canvas = c;
    }    /**
     * Draws the ball at its current position
     * @param g2 the graphics context
     */
    public void draw(Graphics2D g2) {
        g2.fill(new Ellipse2D.Double(x, y, XSIZE, YSIZE));
    }    /**
     * Moves the ball to the next position, reversing direction
     * if it hits one of the edges
     */
    public void move() {
        canvas.repaint();
    }    /* 画布 */
    private Component canvas;    /* ball的宽度 */
    private static final int XSIZE = 10;    /* ball的高度 */
    private static final int YSIZE = 10;    /* ball的初始位置的X坐标 */
    private int x = 0;    /* ball的初始位置的Y坐标 */
    private int y = 0;    /* ball每次移动的X坐标长度 */
    private int dx = 10;    /* ball每次移动的Y坐标长度 */
    private int dy = 10;}

没错。焦点就是在JButton上。现在的问题是，我不知道他是如何获得焦点的。也不知道该如何让别的组件获得焦点。

那我的问题应该如何解决？如何让shit　Canvas获得焦点。

把JButton换成JLabel试试？它是没有焦点的。这个问题没考虑过，纯属瞎猜^_^

其实我以前也碰到过类似的问题，后来实在解决不了，就在每个能获得焦点的控件里加了KeyListener
方法比较笨，后来也就没怎么研究过！希望楼下的能有好的解决办法！

OOOOOOOOOOK。问题解决。问题在于，原代码中给canvas设置焦点后。会执行addButton(),添加Button,结果将焦点又转移到了Button上。
因此需要在button之后给canvas设置焦点。我将Frame中的canvas.requestFocus(true)挪到了addBall()方法中。
Frame代码如下：/**
* The frame with canvas and buttons.
*/
class BounceFrame extends JFrame {    /**
     * Constructs the frame with the canvas for showing the
     * bouncing ball and Start and Close buttons
     */
    public BounceFrame() {
        setSize(WIDTH, HEIGHT);
        setTitle("BounceThread");
        setLocation(112, 84);        Container contentPane = this.getContentPane();
        canvas = new BallCanvas();
        contentPane.add(canvas, BorderLayout.CENTER);

        JPanel buttonPanel = new JPanel();
        addButton(buttonPanel, "Start", new ActionListener() {
            public void actionPerformed(ActionEvent evt) {
                addBall();
            }
        });
        addButton(buttonPanel, "Close", new ActionListener() {
            public void actionPerformed(ActionEvent evt) {
                System.exit(0);
            }
        });
        contentPane.add(buttonPanel, BorderLayout.SOUTH);

    }    /**
    Adds a button to a container.
    @param c the container
    @param title the button title
    @param listener the action listener for the button
    */
    public void addButton(Container c, String title, ActionListener listener) {
        JButton button = new JButton(title);
        c.add(button);
        button.addActionListener(listener);
    }    /**
    Adds a bouncing ball to the canvas and starts a thread
    to make it bounce
    */
    public void addBall() {
        Ball b = new Ball(canvas);
        canvas.add(b);
        canvas.requestFocus(true);
        BallThread thread = new BallThread(b);
        thread.start();
    }    private BallCanvas canvas;
    public static final int WIDTH = 800;
    public static final int HEIGHT = 600;}
感谢各位的积极参与并给了我启示，我是新手分不多，但见者有份，以示鼓励。谢谢。

调试易

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