GUI问题 ,请求帮助
import java.awt.*;
import javax.swing.*;
public class GridLayoutDemo {
private JFrame frame;
private JButton b1,b2,b3,b4,b5,b6;
public static void main(String args[]) {
GridLayoutDemo that=new GridLayoutDemo();
that.go();
}
public void go() {
frame=new JFrame("Grid example");
Container contentPane=frame.getContentPane();
contentPane.setLayout(new GridLayout(3,2));
b1=new JButton("grid_1");
b2=new JButton("grid_2");
b3=new JButton("grid_3");
b4=new JButton("grid_4");
b5=new JButton("grid_5");
b5=new JButton("grid_6");
contentPane.add(b1);
contentPane.add(b2);
contentPane.add(b3);
contentPane.add(b4);
contentPane.add(b5);
contentPane.add(b6);
frame.pack();
frame.setVisible(true);
}
}
异常显示如下:
Exception in thread "main" java.lang.NullPointerException
at java.awt.Container.addImpl(Container.java:1041)
at java.awt.Container.add(Container.java:365)
at GridLayoutDemo.go(GridLayoutDemo.java:29)
at GridLayoutDemo.main(GridLayoutDemo.java:10)