contentPane和水平居中

package cn.rushangw.lesson04;

import javax.swing.*;
import java.awt.*;

public class JFrameDemo02 {
    public static void main(String[] args) {
        new MyJFrame2().init();
    }
}

class MyJFrame2 extends JFrame{
    public void init(){
        setBounds(1,1,200,200);
        setVisible(true);
        JLabel jLabel = new JLabel("什么是快乐星球？");
        add(jLabel);
        //设置水平对齐
        jLabel.setHorizontalAlignment(SwingConstants.CENTER);
        //获得一个容器
        Container contentPane = getContentPane();
        contentPane.setBackground(Color.cyan);

    }
}