java button 按钮插入图片不显示

package cn.zzz;

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.GridLayout;
import java.awt.Insets;
//import javax.swing.*;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.SwingConstants;
public class TestFrame extends JFrame{
public static void main(String[] args){
TestFrame frame=new TestFrame();
frame.setVisible(true);
}
public TestFrame(){
super(/*"woaijava"*/);
setTitle("我的第一个JFrame");
setBounds(100,100,300,300);
setResizable(false);
getContentPane().setLayout(null);
//getContentPane().setBackground(Color.pink);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

/*final JPanel viewPanel=new JPanel();
Container panel=getContentPane();

panel.add(viewPanel,BorderLayout.NORTH);
JTextField textField=new JTextField();
textField.setEditable(false);
textField.setHorizontalAlignment(SwingConstants.RIGHT);
textField.setColumns(18);
viewPanel.add(textField);
final JPanel buttonPanel=new JPanel();
final GridLayout gridLayout=new GridLayout(4,0);
gridLayout.setHgap(10);
gridLayout.setVgap(10);
buttonPanel.setLayout(gridLayout);
panel.add(buttonPanel,BorderLayout.CENTER);

String[][]names={{"1","2","3","+"},
{"4","5","6","-"},{"7","8","9","*"},{".","0","=","/"}};
JButton[][] buttons= new JButton[4][4];
for(int row=0;row<names.length;row++){
for(int col=0;col<names.length;col++){
buttons[row][col] = new JButton(names[row][col]);
buttonPanel.add(buttons[row][col]);
}
}
final JLabel leftLabel =new JLabel();
leftLabel.setPreferredSize(new Dimension(10,0));
getContentPane().add(leftLabel,BorderLayout.WEST);
final JLabel rightLabel=new JLabel();
rightLabel.setPreferredSize(new Dimension(10,0));
panel.add(rightLabel,BorderLayout.EAST);*/
//final JPanel button1Panel=new JPanel();
JButton button=new JButton();
button.setMargin(new Insets(0,0,0,0));
button.setText("button");
button.setContentAreaFilled(false);
button.setBorderPainted(false);
button.setIcon(new ImageIcon("4.png"));
button.setRolloverIcon(new ImageIcon("4.png"));
button.setPressedIcon(new ImageIcon("4.png"));
button.setBounds(100,10,100,100);
getContentPane().add(button);

}
}
图片导入到scr文件夹和包里面都没用 图片途径有问题吗？
只需要看最后那一段代码 按钮那部分

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