当父帧设置为不可调整大小时，JPanel会调整大小

Question

已经建立了一个小的测试SWING应用程序，有三个面板。一个主JPanel，包含两个较小的JPanel。一个在左边（板面板），另一个在右边（侧板）。通过调用min、preferred和max size方法，两个内部面板都被设置为请求的特定大小。右面板中的一个按钮将父JFrame设置为not re-sizable。在父帧设置为不可调整大小之前，一切看起来都很好，这会导致（？！）调整框架和主面板的大小，使其变得更大。

寻找为什么要调整大小，以及可以做什么来保持主面板和框架的大小，以仅包围两个内部面板，而不是更多，一旦框架被冻结。

谢谢你的帮助和洞察力！

编辑：显示此问题在JRE8中。在JRE9中，它消失了，但引入了一个缩放问题。整个应用程序在运行Windows10的4K显示器上得到放大。

package org.fubar;

import javax.swing.BorderFactory;
import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Toolkit;
import java.awt.Window;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class PanelTest {

    private static final String appTitle    = "JPanel Test by Fubar.org(c)";

    public static JFrame myFrame                    = null;
    public static JPanel mainPanel                  = null;
    public static JPanel boardPanel                 = null;
    public static JPanel sidePanel                  = null;

    public static void main(String[] args) {

        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();
            }
        });
    }

    private static void createAndShowGUI() {

        System.out.println("Create and show GUI");

        JFrame myFrame = new JFrame(appTitle);
        myFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        mainPanel = new MainPanel();
        myFrame.add(mainPanel);

        myFrame.pack();
        centreWindow(myFrame);
        myFrame.setVisible(true);
    }

    public static void centreWindow(Window frame) {
        Dimension dimension = Toolkit.getDefaultToolkit().getScreenSize();
        int x = (int) ((dimension.getWidth() - frame.getWidth()) / 2);
        int y = (int) ((dimension.getHeight() - frame.getHeight()) / 2);
        frame.setLocation(x, y);
    }

    public static void barfSize(JPanel panel, String panelName) {
        Dimension panelSize = panel.getSize();
        System.out.println(String.format("%s size:(%d,%d);",panelName,panelSize.width,panelSize.height));
    }

}

class MainPanel extends JPanel {

    static final long serialVersionUID = 1;

    public MainPanel() {

        setBorder(BorderFactory.createLineBorder(Color.green));

        setLayout(new BoxLayout(this, BoxLayout.X_AXIS));

        PanelTest.boardPanel = new BoardPanel();
        PanelTest.boardPanel.setAlignmentY(TOP_ALIGNMENT);
        add(PanelTest.boardPanel);

        PanelTest.sidePanel = new SidePanel();
        PanelTest.sidePanel.setAlignmentY(TOP_ALIGNMENT);
        add(PanelTest.sidePanel);

    }

    public void paintComponent(Graphics gooey) {
        super.paintComponent(gooey);
        PanelTest.barfSize(this, "Main Panel");
    }

}

class BoardPanel extends JPanel {

    static final long serialVersionUID = 1;

    public BoardPanel() {

        setBorder(BorderFactory.createLineBorder(Color.red));

        Dimension mySize = new Dimension(400,200);
        setMinimumSize(mySize);
        setPreferredSize(mySize);
        setMaximumSize(mySize);

        JLabel lblText = new JLabel("Board Panel");
        add(lblText);

    }

    public void paintComponent(Graphics gooey) {
        super.paintComponent(gooey);
        PanelTest.barfSize(this, "Board Panel");
    }
}

class SidePanel extends JPanel implements ActionListener {

    static final long serialVersionUID = 1;

    public SidePanel() {

        setBorder(BorderFactory.createLineBorder(Color.blue));

        Dimension mySize = new Dimension(200,200);
        setMinimumSize(mySize);
        setPreferredSize(mySize);
        setMaximumSize(mySize);

        JLabel lblText = new JLabel("Side Panel");
        add(lblText);

        JButton btnFreeze = new JButton("Freeze");
        btnFreeze.setActionCommand("Freeze");      
        btnFreeze.setToolTipText("Click me to freeze frame");
        btnFreeze.setBorderPainted(true);
        btnFreeze.setEnabled(true);
        btnFreeze.addActionListener(this);
        add(btnFreeze);

    }

    public void actionPerformed(ActionEvent action) {
        String command = action.getActionCommand();
        if ( command == "Freeze") {
            freezeFrame();
            System.out.println("Froze frame.");
        }
        Dimension panelSize = getSize();
        System.out.println(String.format("Side Panel size:(%d,%d);",panelSize.width,panelSize.height));
    }

    public void paintComponent(Graphics gooey) {
        super.paintComponent(gooey);
        PanelTest.barfSize(this, "Side Panel");
    }

    public void freezeFrame() {
        JFrame topFrame = (JFrame) SwingUtilities.getWindowAncestor(this);
        Dimension parentSize = this.getParent().getSize();
        topFrame.setMaximumSize(parentSize);
        topFrame.setResizable(false);
    }

}

屏幕帽1:
在框架调整大小之前禁用应用程序

Create and show GUI
Main Panel size:(602,202);
Side Panel size:(200,200);
Board Panel size:(400,200);
Main Panel size:(602,202);
Side Panel size:(200,200);
Board Panel size:(400,200);
Froze frame.
Side Panel size:(200,200);
Main Panel size:(618,218);
Side Panel size:(200,200);
Board Panel size:(400,200);
Main Panel size:(618,218);
Side Panel size:(200,200);
Board Panel size:(400,200);

Answer 1

如果您在首次创建JFrame时将其设置在setResizable（false）上，则不会出现问题。

    JFrame myFrame = new JFrame(appTitle);
    myFrame.setResizable(false);