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 stubnew JButtonTest();}}