Question

Simple question – why wouldn’t an object move if it’s the object of .move() inside onMouseMoved()? I’m trying to write Breakout as part of the Stanford 106A exercises on iTunes U and for some reason I can’t get the paddle to track the mouse. I’m a java noob, so I’m sure it’s something really simple. Could someone please take a look at this code?

/** Runs the Breakout program. */
    public void run() {
        setupBoard();
        addMouseListeners();
    }

    /** Provides the initial GCanvas and blocks for the game */
    private void setupBoard(){
        this.setSize(APPLICATION_WIDTH,APPLICATION_HEIGHT);
        addBricks();
        paddle = new GRect(PADDLE_WIDTH, PADDLE_HEIGHT);
        add(paddle, WIDTH/2-PADDLE_WIDTH/2,HEIGHT-PADDLE_Y_OFFSET);

    }

    public void MouseMoved(MouseEvent e){
        paddle.move(e.getX()-paddle.getX(), 0);
        }

    private GRect paddle;
}

I’m not sure if having paddle be an instance variable is appropriate in this case, since its “value” doesn’t change (the paddle’s always the paddle), but if I just define it as a new GRect within setupBoard I get an error in the MouseMoved() method.

Answer 1

Your class that has the mouseMoved() method needs to implement the interface MouseMotionListener, and add the motion listener. Moreover, the event handler is mouseMoved() not MouseMoved(). So, e.g.:

public class Game extends JPanel implements MouseMotionListener {
    public void run() {
        addMouseMotionListener(this);
        //...        
    }
    public void mouseMoved(MouseEvent e) {                  
        paddle.move(e.getX()-paddle.getX(), 0); 
    } 
    //...
};