形状在绘图面板Java上不移动

Question

i am trying to make a simple java game with a bat(paddle) and ball. So far i have painted the 2 objects onto the panel, however i cant get them to move. i have added key events for the bat and a move() method for the ball. Below are all my classes.

Game class:

public class Game extends JFrame {

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                new Game();
            }});
    }

    MyDrawingPanel myDrawingPanel = new MyDrawingPanel(this);
    MyUIPanel myUIPanel = new MyUIPanel(this);


    public Game()
    {
        setSize(1160,660); // you may change frame and panel sizes
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        Container cp = getContentPane();    
        cp.setLayout(new FlowLayout());
        cp.add(myDrawingPanel);
        cp.add(myUIPanel);

        setVisible(true);
    }
}

MyDrawingPanel class:

class MyDrawingPanel extends JPanel {

    Game game;

    Ball ball = new Ball(this);
    Bat bat = new Bat(this);

    public MyDrawingPanel(Game game)
    {
        this.game=game;
        setPreferredSize(new Dimension(800,600));
        setBackground(Color.RED);
        requestFocus();
    }

    public void paint(Graphics g)
    {
        super.paint(g);
        Graphics2D g2d = (Graphics2D) g;
        g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING,RenderingHints.VALUE_ANTIALIAS_ON);
        ball.paint(g2d);

        Graphics2D gBat = (Graphics2D) g;
        bat.paint(gBat);
    }
}

Ball class:

public class Ball {

    int x = 0;
    int y = 0;
    int xa = 1;
    int ya = 1;
    private MyDrawingPanel myDrawingPanel;

    public Ball(MyDrawingPanel myDrawingPanel) {
        this.myDrawingPanel = myDrawingPanel;
    }

    public void move() {
        if (x + xa < 0)
            xa = 1;
        if (x + xa > myDrawingPanel.getWidth() - 30)
            xa = -1;
        if (y + ya < 0)
            ya = 1;
        if (y + ya > myDrawingPanel.getHeight() - 30)
            ya = -1;

        x = x + xa;
        y = y + ya;
    }

    public void paint(Graphics2D  g) {
        g.fillOval(x, y, 30, 30);
    }
}

Bat class:

public class Bat{

    int x = 0;
    int xa = 0;
    private MyDrawingPanel myDrawingPanel;

    public Bat(MyDrawingPanel myDrawingPanel)
    {
        this.myDrawingPanel = myDrawingPanel;
    }

    public void move(){
        if(x + xa > 0 && x + xa <myDrawingPanel.getWidth()-60 )
            x = x + xa;
    }

    public void paint(Graphics2D g)
    {
        g.setColor(Color.BLUE);
        g.fillRoundRect(x, 500, 100, 20, 10, 10);
    }

    public void keyPressed(KeyEvent e)
    {
        if(e.getKeyCode() == KeyEvent.VK_LEFT)
            xa = -1;
        if(e.getKeyCode() == KeyEvent.VK_RIGHT)
            xa = 1;
    }

    public void keyReleased(KeyEvent e)
    {
        xa = 0;
    }
}

Answer 1

Methods such as keyPressed and keyReleased don't do anything without a KeyListener implementation. So currently, your methods are useless. What you should do have the DrawingPanel class implement the KeyListener , like this

public class DrawingPanel extends JPanel implements KeyListener {
    ...
}

The methods, keyPressed and keyReleased should be in that class. You'll also want setter methods for what ever variables are updated in the Bat class, like x and xa , is those are the variables that determine the movement of the Bat .

So in the keyPressed , which should be in the DrawingPanel class, it could look something like this

public void keyPressed(KeyEvent e) {
    if (e.getKeyCode() == KeyEvent.VK_LEFT) {
        bat.setXa(bat.getXa() - 1);
        repaint();
    }
    if (e.getKeyCode() == KeyEvent.VK_RIGHT) {
        bat.setXa(1);
        repaint();
    }
}

Notice how I call repaint() . That's what you need to do after you move something.

This should get you started in the right direction

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EDIT

Forget the majority of the above answer.

Instead of using a KeyListener though I would recommeng using key binding. You may face focus problems using KeyListener . I implemented the keybinding for the DrawingPanel and it works fine. It'll give you some ideas to work with.

 class MyDrawingPanel extends JPanel { Game game; Ball ball = new Ball(this); Bat bat = new Bat(this); public MyDrawingPanel(Game game) { this.game = game; setPreferredSize(new Dimension(800, 600)); setBackground(Color.RED); requestFocus(); Action rightAction = new AbstractAction() { public void actionPerformed(ActionEvent e) { bat.x += 10; repaint(); } }; Action leftAction = new AbstractAction() { public void actionPerformed(ActionEvent e) { bat.x -= 10; repaint(); } }; InputMap inputMap = getInputMap(JPanel.WHEN_IN_FOCUSED_WINDOW); ActionMap actionMap = getActionMap(); inputMap.put(KeyStroke.getKeyStroke("RIGHT"), "rightAction"); actionMap.put("rightAction", rightAction); inputMap.put(KeyStroke.getKeyStroke("LEFT"), "leftAction"); actionMap.put("leftAction", leftAction); } public void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2d = (Graphics2D) g; g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON); ball.paint(g2d); Graphics2D gBat = (Graphics2D) g; bat.paint(gBat); } } 

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See How to use key bindings