input == null! atImageIO.read(Unknown Source）

import java.awt.Graphics;
import java.awt.Image;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.net.URL;

import javax.swing.JFrame;

public class PhotoTest extends JFrame{
Image img;
double x,y;

public void LaunchFrame(){
    new PaintThread().start();
    setSize(700,700);
    setVisible(true);
    setDefaultCloseOperation(EXIT_ON_CLOSE);
}

public PhotoTest(double x,double y,String path){
    this.x=x;
    this.y=y;
    img=Util.getImage(path);
}

public void paint(Graphics g){
    g.drawImage(img, (int)x,(int)y,null);
}

static class Util{
    public static Image getImage(String path){
        BufferedImage img=null;
        URL u=PhotoTest.class.getClassLoader().getResource(path);
        try {
            img=javax.imageio.ImageIO.read(u);
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return img;
    }
}

class PaintThread extends Thread{
    public void run(){
    while(true){
        repaint();
        try {
            Thread.sleep(300);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    }
}
public static void main(String[] args) {
    new PhotoTest(0,0,"PhotoTest/xingkong.png").LaunchFrame();
}

}

http://www.cnblogs.com/stansonwilliam/archive/2012/10/26/2740471.html