为什么用java的URL定位资源图片需要刷新界面才能显示

package gameFile;

import javax.swing.*;

import java.applet.AudioClip;

import java.awt.Color;

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 java.util.HashMap;

@SuppressWarnings("serial")

public class G1P4 extends JFrame {

final int WIDTH = 900, HEIGHT = 650;

final int UP = 0, RIGHT = 1, DOWN = 2, LEFT = 3;

int p1Direction = UP;

int p2Direction = UP;

boolean winnerChosen = false;

int p1Laps = 0, p2Laps = 0;

// BackGroundMusic bgm=new BackGroundMusic("e://111.wav");

HashMap<String, Rectangle> border = new HashMap<String, Rectangle>();

double p1Speed = .5, p2Speed = .5;

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 / 9) * 10,

HEIGHT / 9);

Rectangle center = new Rectangle((int) ((WIDTH / 9) * 2.5),

(int) ((HEIGHT / 9) * 2.5), (int) ((WIDTH / 9) * 5),

(HEIGHT / 9) * 4);

Rectangle obstacle = new Rectangle(WIDTH / 2, (int) ((WIDTH / 9) * 5.3),

WIDTH / 10, (int) (HEIGHT / 4.2));

Rectangle obstacle2 = new Rectangle((int) (WIDTH / 3),

(int) ((HEIGHT / 9) * 5), WIDTH / 10, HEIGHT / 4);

Rectangle obstacle3 = new Rectangle((int) (2 * WIDTH / 3),

(int) ((HEIGHT / 9) * 5), WIDTH / 10, HEIGHT / 4);

Rectangle obstacle4 = new Rectangle(WIDTH / 3, (int) ((HEIGHT / 9)),

WIDTH / 15, HEIGHT / 9);

Rectangle obstacle5 = new Rectangle(WIDTH / 2, (int) ((WIDTH / 9) * 1.3),

WIDTH / 30, HEIGHT / 4);

Rectangle finish = new Rectangle(WIDTH / 9, HEIGHT / 2 - HEIGHT / 9,

(int) (WIDTH / 9 * 1.5), HEIGHT / 70);

Rectangle line = new Rectangle(WIDTH / 9, HEIGHT / 2, WIDTH / 30,

HEIGHT / 140);

Rectangle line1 = new Rectangle(WIDTH / 9 + (int) ((WIDTH / 9) * 1.5 / 2),

HEIGHT / 2 + HEIGHT / 10, (int) ((WIDTH / 9) * 1.5) / 2,

HEIGHT / 140);

Rectangle p1 = new Rectangle(WIDTH / 9, HEIGHT / 2, WIDTH / 30, WIDTH / 30);

Rectangle p2 = new Rectangle(WIDTH / 9 + ((int) (WIDTH / 9 * 1.5 / 2)),

HEIGHT / 2 + HEIGHT / 10, WIDTH / 30, WIDTH / 30);

Image myImage[] = new Image[8];

URL url = null;

Image img;

public G1P4() {

super("Radical Racing");

this.setSize(WIDTH / 9 * 10, HEIGHT / 9 * 10);

this.setVisible(true);

this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

border.put("left", left);

border.put("right", right);

border.put("top", top);

border.put("bottom", bottom);

border.put("center", center);

border.put("obstacle", obstacle);

border.put("obstacle2", obstacle2);

border.put("obstacle3", obstacle3);

border.put("obstacle4", obstacle4);

border.put("obstacle5", obstacle5);

System.out.println(getClass().getResource(""));

try {

url = this.getClass().getResource("p11.png");

img=Toolkit.getDefaultToolkit().getImage(url);

img.getSource();

System.out.println("LAILE"+img.getHeight(null));

System.out.println("LAILE"+img.getHeight(null));

} catch (Exception e) {

e.printStackTrace();

}

// JOptionPane.showMessageDialog(null, "Welcome hero!!!");

try{

URL eng=this.getClass().getResource("111.wav");

AudioClip snd=JApplet.newAudioClip(eng);

snd.play();

System.out.println(eng);

}catch(Exception e){

e.printStackTrace();

}

}

@Override

public void paint(Graphics g) {

super.paint(g);

g.drawImage(img, 0, 0, null);

// this.doHitCheck();

}

public static void main(String[] args) {

new G1P4();

}

}

//图片放在bin/gameFile目录下，应该不是路径问题