画布上的物体 - 斯坦福突破 - 划桨飞离屏幕

Question

我正在进行斯坦福在线Java课程，我在移动划桨时遇到了麻烦。我的mouselistener已全部连接起来，它产生的值似乎与我的鼠标正在做的一样。我从最后一个位置减去当前位置，这应该给我的桨的翻译值，但是有点麻烦。当我加载它时，屏幕底部出现了桨叶，但只要鼠标进入屏幕，桨就会飞走!!

注意 - 我已将输出包含到控制台中以显示应更新到paddle对象的X位置的值流。

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;

public class Breakout extends Canvas implements MouseMotionListener, MouseListener{
    private final int WIN_WIDTH = 500;
    private final int WIN_HEIGHT = 700;
    private final int BRICK_Y_POSITION =  100;
    private final int BRICK_HEIGHT = 10;
    private final int BRICK_WIDTH = 30;
    //Create the paddle
    private final int paddleYPosition = 500;
    private int lastX = 0;
    private int currentX = 0;
    brick paddle = new brick(0,paddleYPosition, BRICK_WIDTH+20, BRICK_HEIGHT);

    //Create Canvas object that implements the MouseListener and KeyListener
    public Breakout(){
        super();
        addMouseListener(this);
        addMouseMotionListener(this);
        setBackground(Color.gray);
    }

    public void makeBricks(Graphics g, Color color, int yPosition){
        int xSpacer = 0;
        int ySpacer = 0;
        int x = 15;

        g.setColor(color);
        for (int j= 0; j<2; j++){
            for (int i=0; i<13; i++){
                g.fillPolygon(new brick (x + xSpacer , yPosition + ySpacer , BRICK_WIDTH , BRICK_HEIGHT));      
                xSpacer+=35;}
            ySpacer+=15;
            xSpacer = 0;
        }
    }

    public void paint (Graphics g){         
        makeBricks(g, Color.red, BRICK_Y_POSITION);
        makeBricks(g, Color.orange, BRICK_Y_POSITION+30);
        makeBricks(g, Color.yellow, BRICK_Y_POSITION+60);
        makeBricks(g, Color.green, BRICK_Y_POSITION+90);
        makeBricks(g, Color.cyan, BRICK_Y_POSITION+ 120);
        g.setColor(Color.black);
        g.fillPolygon(paddle);
        paddle.translate(currentX - lastX, paddleYPosition);
    }       

    public void mouseClicked(MouseEvent e) {}
    public void mouseEntered(MouseEvent e) {}   
    public void mouseExited(MouseEvent e) {}
    public void mousePressed(MouseEvent e) {}
    public void mouseReleased(MouseEvent e) {}
    public void mouseDragged(MouseEvent e) {}
    public void mouseMoved(MouseEvent e) {
        if (10 <= e.getX() && e.getX() <=490){
            currentX = e.getX();
            System.out.println(currentX-lastX);
            lastX = currentX;
        }
        repaint();
    }       

    public static void main(String[] args){
        //Create canvas
        Breakout canvas = new Breakout();
        //Create JFrame to hold the canvas
        JFrame win = new JFrame("Breakout!");
        win.setSize(500,700);

        //Add all of the visual elements to the JFrame window
        win.add(new JLabel("TitledBorder using LineBorder"));
        win.add(canvas);

        win.setVisible(true);
        win.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    }
}