我知道这不是第一次提出这个问题，但回复对我没什么帮助，所以我正在帮助我终于得到答案
我制作了这个小游戏，我在轨道上开了一个汽车（必须使用矩形）。当我使用repaint()方法时，代表汽车的矩形在新位置重新绘制，但留下了一条痕迹。
我有这段代码：
import java.awt.Color;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.Rectangle;
import java.awt.Toolkit;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.net.URL;
import javax.swing.JFrame;
import javax.swing.JPanel;
@SuppressWarnings("serial")
public class MAP extends JFrame
{
//constant for the screen size and used for the drawing the terrain
final int WIDTH = 900, HEIGHT = 650;
//the URL and Img designed for the images
URL cLeft,cRight,cUp;
Image img1,img2,img3;
//these will keep track of each player’s speed:
double p1Speed =.5;
//these are ints that represent directions:
final int UP = 0, RIGHT = 1, DOWN = 2, LEFT = 3;
//these will keep track of the player’s directions (default = up)
int p1Direction = 0;
JPanel panel;
//draw the terrain
Rectangle left = new Rectangle(0,0,WIDTH/9,HEIGHT);
Rectangle right = new Rectangle((WIDTH/9)*9,0,WIDTH/9,HEIGHT);
Rectangle top = new Rectangle(0,0,WIDTH, HEIGHT/9);
Rectangle bottom = new Rectangle(0,(HEIGHT/9)*9,WIDTH,HEIGHT/9);
Rectangle center = new Rectangle((int)((WIDTH/9)*2.5),(int)((HEIGHT/9)*2.5),(int)((WIDTH/9)*5),(HEIGHT/9)*4);
//these obstacles will obstruct the path and make navigating harder
Rectangle obstacle = new
Rectangle(WIDTH/2,(int)((HEIGHT/9)*7),WIDTH/10,HEIGHT/9);
Rectangle obstacle2 = new
Rectangle(WIDTH/3,(int)((HEIGHT/9)*5),WIDTH/10,HEIGHT/4);
Rectangle obstacle3 = new
Rectangle(2*(WIDTH/3),(int)((HEIGHT/9)*5),WIDTH/10,HEIGHT/4);
Rectangle obstacle4 = new Rectangle(WIDTH/3,HEIGHT/9,WIDTH/30,HEIGHT/9);
Rectangle obstacle5 = new Rectangle(WIDTH/2,(int)((HEIGHT/9)*1.5),WIDTH/30,HEIGHT/4);
Rectangle finish = new Rectangle(WIDTH/9,(HEIGHT/2)-HEIGHT/9,(int)((WIDTH/9)*1.5),HEIGHT/70);
Rectangle lineO=new Rectangle(WIDTH/9,HEIGHT/2,(int)((WIDTH/9)*1.5)/2,HEIGHT/140);
Rectangle lineI = new Rectangle(((WIDTH/9)+((int)((WIDTH/9)*1.5)/2)),(HEIGHT/2)+(HEIGHT/10),(int)((WIDTH/9)*1.5)/2, HEIGHT/140);
//this is the rectangle for player 1’s (outer) car:
Rectangle p1 = new Rectangle(WIDTH/9,HEIGHT/2, WIDTH/30,WIDTH/30);
public MAP(){
super("Radical Racing");
setSize(WIDTH,HEIGHT);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setVisible(true);
setResizable(false);
setVisible(true);
setLocationRelativeTo(null);
//the following code creates the JFrame
try
{
cUp = this.getClass().getResource("carUp.jpg");
cLeft = this.getClass().getResource("carLeft.jpg");
cRight = this.getClass().getResource("carRight.jpg");
}catch(Exception e)
{}
//attach the URLs to the images
img1 = Toolkit.getDefaultToolkit().getImage(cUp);
img2 = Toolkit.getDefaultToolkit().getImage(cLeft);
img3 = Toolkit.getDefaultToolkit().getImage(cRight);
panel=new JPanel(){
public void paint(Graphics g)
{
//super.paint(g);
//draw the background for the racetrack
g.setColor(Color.DARK_GRAY);
g.fillRect(0,0,WIDTH,HEIGHT);
//when we draw, the border will be green
g.setColor(Color.GREEN);
//fill rectangle
g.fillRect(left.x,left.y,left.width,left.height);
g.fillRect(right.x,right.y,right.width,right.height);
g.fillRect(top.x,top.y,top.width,top.height);
g.fillRect(bottom.x,bottom.y,bottom.width,bottom.height);
g.fillRect(center.x,center.y,center.width,center.height);
g.fillRect(obstacle.x,obstacle.y,obstacle.width,obstacle.height);
g.fillRect(obstacle2.x,obstacle2.y,obstacle2.width,obstacle2.height);
g.fillRect(obstacle3.x,obstacle3.y,obstacle3.width,obstacle3.height);
g.fillRect(obstacle4.x,obstacle4.y,obstacle3.width,obstacle4.height);
g.fillRect(obstacle5.x,obstacle5.y,obstacle5.width,obstacle5.height);
//set the starting line color to white
g.setColor(Color.WHITE);
//now draw the starting line
g.fillRect(lineO.x,lineO.y,lineO.width,lineO.height);
g.fillRect(lineI.x,lineI.y,lineI.width,lineI.height);
//set the color of the finish line to yellow
g.setColor(Color.YELLOW);
//now draw the finish line
g.fillRect(finish.x,finish.y,finish.width,finish.height);
//set the color to blue for p1
g.setColor(Color.WHITE);
//now draw the actual player
g.fill3DRect(p1.x,p1.y,p1.width,p1.height,true);
//draw the images for the player
if(p1Direction==UP)
g.drawImage(img1,p1.x,p1.y,this);
if(p1Direction==LEFT)
g.drawImage(img2,p1.x,p1.y,this);
if(p1Direction==RIGHT)
g.drawImage(img3,p1.x,p1.y,this);
}
};
panel.setPreferredSize(new Dimension(950,600));
this.add(panel);
pack();
Move1 move=new Move1();
move.start();
}
private class Move1 extends Thread implements KeyListener
{
public void run()
{
//now, this should all be in an infinite loop, so the process
//repeats
addKeyListener(this);
while(true)
{
//now, put the code in a try block. This will let the
//program exit
//if there is an error.
try
{
//increase speed a bit
// if(p1Speed<=5)
// p1Speed+=.2;
//p1.y-=(int) p1Speed;
if(p1.intersects(left) || p1.intersects(right) || p1.intersects(top) ||
p1.intersects(bottom) || p1.intersects(obstacle) || p1.intersects(obstacle2)||
p1.intersects(obstacle3) || p1.intersects(obstacle4) || p1.intersects(obstacle5))
{
p1Speed = -5;
}
//if the car hits the center, do the same as above
//but make the speed -2.5.
if(p1.intersects(center))
{
p1Speed = -2.5;
}
//increase speed a bit
if(p1Speed<=5)
p1Speed+=.2;
//these will move the player based on direction
if(p1Direction==UP)
{
p1.y-=(int)p1Speed;
}
if(p1Direction==DOWN)
{
p1.y+=(int)p1Speed;
}
if(p1Direction==LEFT)
{
p1.x-=(int)p1Speed;
}
if(p1Direction==RIGHT)
{
p1.x+=(int)p1Speed;
}
panel.repaint();
//this delays the refresh rate:
Thread.sleep(200);
}
catch(Exception e)
{
//if there is an exception (an error), exit the loop.
break;
}
}
}
@Override
public void keyPressed(KeyEvent arg0) {
// TODO Auto-generated method stub
}
@Override
public void keyReleased(KeyEvent arg0) {
// TODO Auto-generated method stub
}
@Override
public void keyTyped(KeyEvent event) {
if(event.getKeyChar()=='a')
{
p1Direction = LEFT;
}
if(event.getKeyChar()=='s')
{
p1Direction = DOWN;
}
if(event.getKeyChar()=='d')
{
p1Direction = RIGHT;
}
if(event.getKeyChar()=='w')
{
p1Direction = UP;
}
}
}
//this starts the program by calling the constructor:
public static void main (String[ ] args)
{
new MAP();
}
}
答案 0 :(得分：1)
在paint方法中取消注释super.paint（g）[第87行]。
它负责清除任何过时对象的画布。
答案 1 :(得分：1)
原因是，在g.fillRect(0,0,WIDTH,HEIGHT);行中，它实际上指的是java.awt.image.ImageObserver#WIDTH和java.awt.image.ImageObserver#HEIGHT，而不是您的实例变量。您可以在任何IDE中看到这一点。
因为预期的黑色背景仅在左上角的1x2像素区域中绘制。由于对super.paint(g);的调用已被注释掉，因此灰色背景甚至都没有重新绘制。因此，汽车的旧图纸不会透支。
需要将代码更改为使用MAP.this.WIDTH，或者需要将WIDTH字段重命名为与从JPanel继承的字段不冲突的字段，或者需要将字段移入相同的JPanel具有更高的优先级，或者您也可以使用JPanel中的getWidth()方法。同样适合身高。