JFrame，留下矩形的痕迹

Question

尝试制作游戏。几乎每次我搬家，它都会留下痕迹

代码：

package lt.mchackers.gametest.main;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Insets;
import java.awt.event.KeyEvent;
import java.awt.image.BufferedImage;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;

import javax.imageio.ImageIO;
import javax.swing.JFrame;

import lt.mchackers.gametest.handlers.InputHandler;

/** 
 * Main class for the game 
 */ 
public class Main extends JFrame 
{
        private static final long serialVersionUID = -828018325337767157L;
        boolean isRunning = true; 
        int fps = 30; 
        int windowWidth = 320; 
        int windowHeight = 320;
        int speed;

        BufferedImage backBuffer; 
        Insets insets; 
        InputHandler input; 

        int x = 0;
        int y = 0;
        int xa = 0;
        int ya = 0;
        Coordinates coords = new Coordinates(0, 0);

        public static void main(String[] args) 
        {       Main game = new Main(); 
                game.run(); 
                System.exit(0); 
        } 

        /** 
         * This method starts the game and runs it in a loop 
         */ 
        public void run() 
        { 
                initialize(); 

                while(isRunning) 
                { 

                        long time = System.currentTimeMillis(); 

                        update(); 
                        draw(); 

                        //  delay for each frame  -   time it took for one frame 
                        time = (1000 / fps) - (System.currentTimeMillis() - time); 

                        if (time > 0) 
                        { 
                                try 
                                { 
                                        Thread.sleep(time); 
                                } 
                                catch(Exception e){} 
                        } 
                } 

                setVisible(false); 
        } 

        /** 
         * This method will set up everything need for the game to run 
         */ 
        void initialize() 
        { 
                setTitle("Game Tutorial"); 
                setSize(windowWidth, windowHeight); 
                setResizable(false); 
                setDefaultCloseOperation(EXIT_ON_CLOSE); 
                setVisible(true); 

                insets = getInsets(); 
                setSize(insets.left + windowWidth + insets.right, 
                                insets.top + windowHeight + insets.bottom); 

                backBuffer = new BufferedImage(windowWidth, windowHeight, BufferedImage.TYPE_INT_RGB); 
                input = new InputHandler(this); 
                Graphics bbg = backBuffer.getGraphics(); 
                BufferedReader reader = null;
                try {
                    reader = new BufferedReader(new FileReader("map"));
                } catch (FileNotFoundException e1) {
                    e1.printStackTrace();
                }
                String line = null;
                try {
                    BufferedImage gray = ImageIO.read(new File("gray.png"));
                    BufferedImage black = ImageIO.read(new File("black.png"));
                    while ((line = reader.readLine()) != null) {
                        for(String s : line.split(""))
                        {
                            if (s.contains("*"))
                            {
                                bbg.drawImage(gray, xa-32, ya, null);
                            }
                            else if (s.contains("#"))
                            {
                                bbg.drawImage(black, xa-32, ya, null);
                            }
                            if (xa < 320)
                            {
                                xa += 32;
                            }
                            else
                            {
                                ya += 32;
                                xa = 0;
                            }
                            System.out.println(xa);
                            System.out.println(ya);
                        }
                    }
                } catch (IOException e) {
                    e.printStackTrace();
                }

        } 

        /** 
         * This method will check for input, move things 
         * around and check for win conditions, etc 
         */ 
        void update() 
        { 
            if (input.isKeyDown(KeyEvent.VK_NUMPAD0))
            {
                speed -= 1;
            }
            if (input.isKeyDown(KeyEvent.VK_NUMPAD1))
            {
                speed += 1;
            }
            if (input.isKeyDown(KeyEvent.VK_RIGHT)) 
            { 
                coords.setCoords(coords.getX() + 32, coords.getY()); 
            } 
            if (input.isKeyDown(KeyEvent.VK_LEFT)) 
            { 
                coords.setCoords(coords.getX() - 32, coords.getY()); 
            } 
            if (input.isKeyDown(KeyEvent.VK_UP))
            {
                coords.setCoords(coords.getX(), coords.getY() - 32); 
            }
            if (input.isKeyDown(KeyEvent.VK_DOWN))
            {
                coords.setCoords(coords.getX(), coords.getY() + 32); 
            }
            //System.out.println(x);
            //System.out.println(y);
            //System.out.println(speed);
            if (coords.getY() < 0)
            {
                coords.setCoords(coords.getX(), 0);
            }
            if (coords.getX() < 0)
            {
                coords.setCoords(0, coords.getY());
            }
            if (coords.getX() > windowWidth - 32)
            {   
                coords.setCoords(windowWidth - 32, coords.getY());
            }
            if (coords.getY() > windowHeight - 32)
            {
                coords.setCoords(coords.getX(), windowHeight - 32); 
            //  y = windowHeight - 32;
            }

        } 

        /** 
         * This method will draw everything 
         */ 
        void draw() 
        {               
                Graphics g = getGraphics(); 
                //this.setBackground(Color.BLACK);
                //super.paintComponents(g);
                backBuffer.setRGB(x, y, Color.BLACK.getRGB());

                Graphics bbg = backBuffer.getGraphics(); 

                BufferedReader reader = null;
                try {
                    reader = new BufferedReader(new FileReader("map"));
                } catch (FileNotFoundException e1) {
                    e1.printStackTrace();
                }
                String line = null;
                try {
                    BufferedImage gray = ImageIO.read(new File("gray.png"));
                    BufferedImage black = ImageIO.read(new File("black.png"));
                    while ((line = reader.readLine()) != null) {
                        for(String s : line.split(""))
                        {
                            if (s.contains("*") && xa + 32!= coords.getX() && ya - 32 != coords.getY())
                            {
                                bbg.drawImage(gray, xa-32, ya, null);
                            }
                            else if (s.contains("#") && xa + 32 != coords.getX() && ya - 32 != coords.getY())
                            {
                                bbg.drawImage(black, xa-32, ya, null);
                            }
                            if (xa < 320)
                            {
                                xa += 32;
                            }
                            else
                            {
                                ya += 32;
                                xa = 0;
                            }
                            //System.out.println(xa);
                            //System.out.println(ya);
                        }
                    }
                } catch (IOException e) {
                    e.printStackTrace();
                }
                bbg.setColor(Color.WHITE); 

                xa = 0;
                ya = 0;
                System.out.println(coords.getX());
                bbg.setColor(Color.WHITE);
                bbg.fillRect(coords.getX(),coords.getY(), 32,32);  
                System.out.println(coords.getY());
                //bbg.setColor(Color.BLACK); 
                //bbg.drawOval(x, y, 20, 20); 


                g.drawImage(backBuffer, insets.left, insets.top, this); 
        } 
}

感谢您的帮助。