使用箭头键时，我的图像消失了

Question

问题是，当我按下向下按钮时，图像（blueboy）消失了，并且它也没有向上移动，但是可以左右移动，我不明白为什么？ 请帮忙。 （我正在使用RealJ）。 如果有一个网站可以在二维滚动游戏方面对我有帮助，那么对我也有帮助。

import java.applet.Applet;
import java.awt.event.*;     
import java.awt.*;  
public class projectblue extends Applet implements     ActionListener,KeyListener,MouseListener {

Image blueboy,trees;    //image variable
int size = 4,jump = 50, cx = 1, cy = 1;    

public void init() {

   blueboy = getImage(getDocumentBase(),"png.png"); 
   trees=     getImage(getDocumentBase(),"background.jpg");
addKeyListener( this ); 
addMouseListener( this );
}

public void paint(Graphics g)
{   
  int width = trees.getWidth(this);     
  int height = trees.getHeight(this);   
  //System.out.println("" + cx +","+ cy);   

  //The later images are drawn on top of the earlier ones.
  g.drawImage(trees, 1 ,1, width*size,height*7,this);
  g.drawImage(blueboy, cx, cy, this);
}

 public void actionPerformed(ActionEvent e) {
 repaint();

}
 public void left(){
      cx = cx -100;
      // blueboy moves left
}

public void keyTyped(KeyEvent e) {
}
public void keyPressed(KeyEvent e) {
 System.out.println("key pressed");
    int key = e.getKeyCode();
    if (key == KeyEvent.VK_LEFT) {
        left();
    }

    if (key == KeyEvent.VK_RIGHT) {
        cx = cx + 100;
        //blueboy moves right
    }

    if (key == KeyEvent.VK_UP) {
        while (cy >= 0 && cy <=1000)
        cy = cy - 100;
            if (cy < 0){
                cy = 1;
               //blueboy moves up, but if it goes out of bounds it goes back to the top
               }
    }

    if (key == KeyEvent.VK_DOWN) {
       while (cy >= 0 && cy <=1000)
        cy = cy + 100;
            if (cy > 1001){
                cy = 999;
               }
        //blueboy moves down, but if it goes out of bounds it goes back to the bottim
    }
    repaint();
}

public void keyReleased(KeyEvent e) {
}

public void mouseEntered( MouseEvent e ) { } 
public void mouseExited( MouseEvent e ) { }
 public void mousePressed( MouseEvent e ) { }
  public void mouseReleased( MouseEvent e ) { }
   public void mouseClicked( MouseEvent e ) {
   int x = getX();
   int y = getY();
System.out.println("clicked at (" + x + ", " + y + ")");
} }

Answer 1

这些while循环将占用您的GUI线程，使动画无用。 如果不是方块，它们应该不是吗？ 另外，还应将所有块括在大括号中。 您的缩进对您而言是谎言，括号将向您显示原因。

另外，您将需要在绘画替代中调用super.paint(g)方法。

另外，这是一项任务吗？如果是，您是否需要使用AWT / Applets而不是Swing进行编码？