在java.awt.Image时，getWidth()和getHeight()为-1的解决方法

import java.applet.*;
import java.awt.Graphics;
import java.awt.Image;

import javax.swing.ImageIcon;

public class ImageRun extends Applet implements Runnable {
Thread t;
int w;
Image img;

public void init() {
w = 0;
img = getImage(getDocumentBase(),"image2.gif");

setSize(600, 400);
}

public void start() {
t = new Thread(this);
t.start();
}

public void stop() {
t = null;
}

public void run() {
img   =   new ImageIcon(img).getImage();	//需要加入此代码
int imgW = img.getWidth(null);
System.out.println(imgW);
while(t != null) {
try{
Thread.sleep(10);
repaint();
w++;
if (w >= getWidth()) {
w = -imgW;
}
} catch(Exception e) {
System.out.println(e.getMessage());
}
}
}

public void paint(Graphics g) {
int h = getHeight() / 2;
g.drawImage(img, w, h, this);
}

public void update(Graphics g) {
paint(g);
}
};