JLabel调整JPanel大小

Question

起初，我只有文本栏和状态栏，如下例所示（我不需要父容器）：

import java.awt.BorderLayout;
import java.awt.Dimension;

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

public class Main
{   
    public static void main(String[] args)
    {           
        //Display actual GUI
        SwingUtilities.invokeLater(new Runnable()
        {
            @Override
            public void run()
            {
                new Gui();
            }
        });
    }
}

class Gui
{   
    public Gui()
    {   
        JFrame masterWindow = new JFrame();

        masterWindow.setSize(1100, 800);
        masterWindow.setMinimumSize(new Dimension(400, 400));
        masterWindow.setLocationRelativeTo(null);
        masterWindow.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JPanel rootPanel = new JPanel();
        rootPanel.setLayout(new BorderLayout());

        StatusBar statusBar = new StatusBar();
        rootPanel.add(statusBar, BorderLayout.SOUTH);

        masterWindow.setContentPane(rootPanel);
        masterWindow.setVisible(true);
    }
}

class StatusBar extends JLabel
{
    private static final long serialVersionUID = 1L;

    StatusBar()
    {   
        super("welcomeText");
        add(textBar);

        setOpaque(true);
        setBorder(BorderFactory.createLoweredSoftBevelBorder());
    }
}

这是应该的。但是，请记住状态栏的高度。现在，如果您将StatusBar类更改为下面的类，那么高度几乎会增加一倍。为什么会这样？

这种设置并不需要更多的垂直空间：

public class StatusBar extends JPanel
{
    private static final long serialVersionUID = 1L;

    StatusBar()
    {
        super();

        JLabel textBar = new JLabel(Main.language.getString("welcomeText"));
        add(textBar);

        setOpaque(true);
        setBorder(BorderFactory.createLoweredSoftBevelBorder());
    }
}

public class StatusBar extends JPanel
{
    private static final long serialVersionUID = 1L;
    JLabel textBar;
    JProgressBar progressBar;

    StatusBar()
    {
        setLayout(new MigLayout("insets 0, gap 0!")); //Mig has some gaps inbetween components, this will remove the gaps

        textBar = new JLabel(Main.language.getString("welcomeText"));

        progressBar = new JProgressBar(0, 100);

        JSeparator separator = new JSeparator(SwingConstants.VERTICAL);

        add(textBar);
        add(separator);
        add(progressBar, "east");

        setOpaque(true);
        setBorder(BorderFactory.createLoweredSoftBevelBorder());
    }
}

我可以让这成为一个新问题，但我觉得不值得...

Answer 1

这是因为，调用super（）将执行超类的无参数构造函数，在您的示例中是JPanel。根据javadoc

JPanel()-创建一个具有双缓冲区和流布局的新JPanel。

因此，当您调用super()时，将创建具有flowlayout的JPanel。