为什么将布局样式应用于我的所有 JPanel？

Question

我正在给自己上一堂重新学习的速成课Java。我正在编写一个非常简单的程序，当您将按钮单击到随机面板时，它会简单地更改按钮的位置。没有真正的问题，我几乎完成了我想要的程序。但是，我想知道为什么当我将布局样式应用于第一个面板 (buttonPanel1) 时，它会自动应用于每个面板？

 /*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package buttonswitch;

import javax.swing.*;
import java.awt.*;
import javax.swing.border.*;
import java.awt.event.*;
import java.util.*;

/**
 *
 * @author Supreme Lenova
 */
import java.util.Random;
public class ButtonWindow extends JFrame{

    private JPanel buttonPanel1;
    private JPanel buttonPanel2;
    private JPanel buttonPanel3;
    private JPanel buttonPanel4;
    private JButton Button;

    private Border raisedbevel, loweredbevel;
    private Border compound;

    public ButtonWindow(){
        setTitle("Button Game");
        setLocation(600,50);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        GridLayout grid = new GridLayout(2,2);
        setLayout(grid);

        raisedbevel = BorderFactory.createRaisedBevelBorder();
        loweredbevel = BorderFactory.createLoweredBevelBorder();
        compound = BorderFactory.createCompoundBorder(raisedbevel, loweredbevel);

        buildPanels();

        Button = new JButton("Click!");
        Button.setAlignmentX(Component.CENTER_ALIGNMENT);
        Button.addActionListener(new ButtonListener());

        buttonPanel1.add(Button);
        buttonPanel1.add(Box.createVerticalGlue());

        setSize(300,300);
        setVisible(true);

}
    private void buildPanels(){
        buttonPanel1 = new JPanel();
        buttonPanel2 = new JPanel();
        buttonPanel3 = new JPanel();
        buttonPanel4 = new JPanel();

        buttonPanel1.setLayout(new BoxLayout(buttonPanel1, BoxLayout.PAGE_AXIS)); 
        buttonPanel1.add(Box.createVerticalGlue());


        buttonPanel1.setBorder(compound);
        buttonPanel2.setBorder(compound);
        buttonPanel3.setBorder(compound);
        buttonPanel4.setBorder(compound);


        this.add(buttonPanel1);
        this.add(buttonPanel2);
        this.add(buttonPanel3);
        this.add(buttonPanel4);
    }



    private class ButtonListener implements ActionListener{

        public void actionPerformed(ActionEvent e){

            generateButton();

        }

        private void generateButton(){
        int last = 5;
        int place = 5;
        Random rand = new Random();
        while(place==last){
        place = rand.nextInt(4)+1;
        }
        last = place;

        switch (place){

            case 1:
                repaint();
                buttonPanel1.add(Button);
                break;
            case 2:
                repaint();
                buttonPanel2.add(Button);
                break;
            case 3:
                repaint();
                buttonPanel3.add(Button);
                break;
            case 4:
                repaint();
                buttonPanel4.add(Button);
                break;


        }
    }

}
}

Answer 1

将布局管理器设置为 buttonPanel1

buttonPanel1.setLayout(new BoxLayout(buttonPanel1, BoxLayout.PAGE_AXIS));
buttonPanel1.add(Box.createVerticalGlue());

不将布局管理器更改为默认使用 FlowLayout 的其他面板。
它会影响按钮大小。打印出来

System.out.println(Button.getSize()); //use button, not Button

现在更改 buttonPanel1

的布局管理器

buttonPanel1.setLayout(new BorderLayout());

并更改代码以将按钮添加到面板：

buttonPanel1.add(Button, BorderLayout.CENTER);

然后重新打印。
布局管理器更改按钮的初始大小。其他3个面板的FlowLayout管理器，不改变大小。

为什么将布局样式应用于我的所有 JPanel？

Why is the Layout style being applied to all of my JPanels?

java

swing

jpanel