at javax.swing.ImageIcon.<init>(Unknown Source)提交按钮组件 例13.11

Exception in thread "main" java.lang.NullPointerException

 at javax.swing.ImageIcon.<init>(Unknown Source)

 at com.txw.JButtonTest.<init>(JButtonTest.java:16)

 at com.txw.JButtonTest.main(JButtonTest.java:46)

package com.txw;
import java.awt.*;
import java.awt.event.*;
import java.net.*;
import javax.swing.*;

public class JButtonTest extends JFrame {
/**
*
*/

private static final long serialVersionUID = 1L;
public JButtonTest(){
//URL url=MyImageIcon.class.getResource("/imageButto.jpg");//多了斜杠要报错
URL url=JButtonTest.class.getResource("/imageButtoo.jpg");//多了斜杠要报错,把斜杠删除，编译通过
Icon icon=new ImageIcon(url);
setLayout(new GridLayout(3,2,5,5));
Container c=getContentPane();
for(int i=0;i<5;i++){
JButton J=new JButton("button"+i,icon);
c.add(J);
if(i%2==0){
J.setEnabled(false);
}
}
JButton jb=new JButton();
jb.setMaximumSize(new Dimension(90,30));
jb.setIcon(icon);
jb.setHideActionText(true);
jb.setToolTipText("pics button");
jb.setBorderPainted(false);
jb.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e){
JOptionPane.showMessageDialog(null, "pop up window");
}
});
c.add(jb);
setTitle("创建带文字与图片的按钮");
setSize(350, 150);
setVisible(true);
setDefaultCloseOperation(WindowConstants.DISPOSE_ON_CLOSE);
}

public static void main(String[] args) {
// TODO Auto-generated method stub
new JButtonTest();

}

}