为什么背景一直是蓝色啊？？

Question

package test1;

import java.awt.*;
import java.awt.Color;

import javax.swing.*;

public class GirdLayout_1 extends JFrame {

String[] str = {"1", "2", "3", "4", "5", "6", "7", "8", "9"};
public GirdLayout_1(){
    super("网格布局");

// this.getContentPane().setBackground(Color.BLACK);
this.getContentPane().setBackground(Color.GRAY);
this.setBounds(200, 200, 500, 500);
this.setDefaultCloseOperation(EXIT_ON_CLOSE);
this.getContentPane().setLayout(new GridLayout(3, 3));
for(int i=0;i<str.length;i++){
if(i==4){
JPanel jp = new JPanel();
// FlowLayout fl = new FlowLayout(FlowLayout.CENTER ,20, 20);
// jp.setLayout(fl);
// GridLayout gl = new GridLayout(2, 2);
// jp.setLayout(gl);
BorderLayout bl = new BorderLayout();
jp.setLayout(bl);
for(int j=4;j<str.length;j++){
switch(j){
case 4: jp.add(new JButton(str[j]), BorderLayout.EAST);break;
case 5: jp.add(new JButton(str[j]), BorderLayout.SOUTH);break;
case 6: jp.add(new JButton(str[j]), BorderLayout.NORTH);break;
case 7: jp.add(new JButton(str[j]), BorderLayout.WEST);break;
case 8: jp.add(new JButton(str[j]), BorderLayout.CENTER);break;
}

            }
            this.getContentPane().add(jp);
        }
        else 
        this.getContentPane().add(new JButton(str[i]));
    }
    this.setVisible(true);
}
public static void main(String arg[]){
    new GirdLayout_1();
}

}

Answer 1

这不是布局正常的颜色吗？GUI 的布局风格本来就是这样的呀。