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

Exception in thread "main" java.lang.NullPointerException  at javax.swing.ImageIcon.(Unknown Source)  at com.txw.JButtonTest.(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