java - JPanel 未正确显示

Question

所以，我从基本的可视化 Java 组件开始，但很难准确地使用它们。

这是我的新问题:我正在尝试实现一个由 3 部分组成的面板:东、中、西，但无法正确显示中心面板。这是我的一段代码:

基本上“panelUpMiddle”不可见，所以我想知道为什么？...

public class TestCode_Web {


public static void main(String[] args) {

    JFrame window = new JFrame("Test");
    window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    window.setSize(400, 400);

    JPanel innerPanel = new JPanel(new BorderLayout());     
    JPanel panelUp = new JPanel(new BorderLayout());

    JPanel panelUpLeft = new JPanel();
    JPanel panelUpMiddle = new JPanel();

    window.add(innerPanel, BorderLayout.NORTH);     
    innerPanel.add(panelUp, BorderLayout.NORTH);

    panelUp.add(panelUpLeft, BorderLayout.WEST);
    panelUp.add(panelUpMiddle, BorderLayout.CENTER);

    JLabel label1 = new JLabel("Label 1");

    JLabel label11 = new JLabel("Label 11");
    JLabel label12 = new JLabel("Label 12");

    panelUp.add(label1);
    panelUpLeft.add(label11);       
    panelUpMiddle.add(label12);     

    panelUp.setBackground(new Color(200, 240, 200));

    panelUpLeft.setBackground(new Color(200, 240, 0));
    panelUpMiddle.setBackground(new Color(100, 240, 200));

    panelUp.setPreferredSize(new Dimension(window.getWidth(), 160));        
    panelUpLeft.setPreferredSize(new Dimension(160, 120));

    window.setVisible(true);
}

}

Answer 1

试试这个代码。我更新了面板和标签的命名，使其更加清晰。

    JFrame window = new JFrame("Test");
    window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    window.setSize(400, 400);

    JPanel centerPanel = new JPanel(new BorderLayout());     
    JPanel eastPanel = new JPanel(new BorderLayout());
    JPanel westPanel = new JPanel(new BorderLayout());

    window.add(centerPanel, BorderLayout.CENTER);     
    window.add(eastPanel, BorderLayout.EAST);
    window.add(westPanel, BorderLayout.WEST);

    JLabel centerLabel = new JLabel("Center");
    JLabel eastLabel = new JLabel("East");
    JLabel westLabel = new JLabel("West");

    eastPanel.add(eastLabel);
    westPanel.add(westLabel);       
    centerPanel.add(centerLabel);

    centerPanel.setPreferredSize(new Dimension(200, 400));
    eastPanel.setPreferredSize(new Dimension(100, 400));
    westPanel.setPreferredSize(new Dimension(100, 400));
    eastPanel.setBackground(new Color(200, 240, 200));
    westPanel.setBackground(new Color(200, 240, 0));

    window.setVisible(true);