JAVA:URL之图像图标

//设计图像图标
import javax.swing.*;
import java.awt.*;
public class TestImageIcon extends JFrame
{
       private ImageIcon icon1 = new ImageIcon("ToolImages/20.gif");//"ToolImages/20.gif"为该project文件夹下的路劲
       private ImageIcon icon2 = new ImageIcon("ToolImages/21.gif");
       private ImageIcon icon3 = new ImageIcon("ToolImages/22.gif");
       public TestImageIcon()
       {
           setLayout(new GridLayout(1,3,5,5));
           add(new JButton(icon1));
           add(new JLabel(icon2));
           add(new JButton(icon3));
        }
        public static void main(String[] agrs)
        {
            JFrame frame = new TestImageIcon();
            frame.setTitle("TestImageIcon");
            frame.setLocationRelativeTo(null);
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.setSize(500,300);
            frame.setVisible(true);
        }
}