在窗体中添加button时 eclipse运行后提示挂起是什么意思是，该怎么改

import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;

public class ButtonFrame extends JFrame{

public ButtonFrame(){
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setBounds(100,100,384,160);
    JPanel contentPane=new JPanel();
    contentPane.setVisible(true);
    contentPane.setBorder(new EmptyBorder(5,5,5,5));;;
    setContentPane(contentPane);
    contentPane.setLayout(null);
    JPanel panel=new JPanel();
    panel.setBounds(0, 0, 368, 122);
    contentPane.add(panel);
    panel.setLayout(null);
    JButton messageButton = new JButton("普通按钮");
    messageButton.setBounds(54, 33, 108, 46);
    panel.add(messageButton);
    java.net.URL url=getClass().getResource("D:/log.png");
    ImageIcon icon=new ImageIcon(url);
    JButton imageButton = new JButton(icon);
    imageButton.setBounds(196, 14, 108, 85);
    panel.add(imageButton);     
}
public static void main(String[] args){
    new ButtonFrame();
}

}

location或者什么变量是否为null