指定顶级容器的ContentPane是否有好处?

https://docs.oracle.com/javase/tutorial/uiswing/components/toplevel.html .

或者“两者都是”表单只是为了向代码的读者清楚地表明jpanel确实要进入jdialog的内容窗格?

import java.awt.Container;
import java.awt.Dimension;
import java.awt.Toolkit;
import javax.swing.BorderFactory;
import javax.swing.BoxLayout;
import javax.swing.JCheckBox;
import javax.swing.JDialog;
import javax.swing.JPanel;
import javax.swing.JRadioButton;

public class DialogTest {

    public static void main(String[] args) {
        DialogContentPane dlgC = new DialogContentPane();
        display(dlgC, "ContentPane");
        DialogJPanel dlgP = new DialogJPanel();
        display(dlgP, "JPanel");
        DialogBoth dlgB = new DialogBoth();
        display(dlgB, "Both");
    }

    public static class DialogContentPane extends JDialog {

        public DialogContentPane() {
            Container contentPane = this.getContentPane();
            contentPane.setLayout(new BoxLayout(contentPane, BoxLayout.Y_AXIS));
            JRadioButton jRadioButton1 = new JRadioButton("My Radio Button, which does nothing");
            jRadioButton1.setBorder(BorderFactory.createEmptyBorder(10, 10, 10, 10));
            contentPane.add(jRadioButton1);
            JCheckBox jCheckBox1 = new JCheckBox("My Check Box, which does nothing either");
            jCheckBox1.setBorder(BorderFactory.createEmptyBorder(10, 10, 10, 10));
            contentPane.add(jCheckBox1);
        }
    }

    public static class DialogJPanel extends JDialog {

        public DialogJPanel() {
            JPanel jPanelOuter = new JPanel();
            jPanelOuter.setLayout(new BoxLayout(jPanelOuter, BoxLayout.Y_AXIS));
            JRadioButton jRadioButton1 = new JRadioButton("My Radio Button, which does nothing");
            jRadioButton1.setBorder(BorderFactory.createEmptyBorder(10, 10, 10, 10));
            jPanelOuter.add(jRadioButton1);
            JCheckBox jCheckBox1 = new JCheckBox("My Check Box, which does nothing either");
            jCheckBox1.setBorder(BorderFactory.createEmptyBorder(10, 10, 10, 10));
            jPanelOuter.add(jCheckBox1);
            this.add(jPanelOuter);
        }
    }

    public static class DialogBoth extends JDialog {

        public DialogBoth() {
            Container contentPane = this.getContentPane();
            contentPane.setLayout(new BoxLayout(contentPane, BoxLayout.Y_AXIS));
            JPanel jPanelOuter = new JPanel();
            jPanelOuter.setLayout(new BoxLayout(jPanelOuter, BoxLayout.Y_AXIS));
            JRadioButton jRadioButton1 = new JRadioButton("My Radio Button, which does nothing");
            jRadioButton1.setBorder(BorderFactory.createEmptyBorder(10, 10, 10, 10));
            jPanelOuter.add(jRadioButton1);
            JCheckBox jCheckBox1 = new JCheckBox("My Check Box, which does nothing either");
            jCheckBox1.setBorder(BorderFactory.createEmptyBorder(10, 10, 10, 10));
            jPanelOuter.add(jCheckBox1);
            contentPane.add(jPanelOuter);
        }
    }

    public static void display(JDialog dlg, String title) {
        Toolkit tk;
        Dimension screenDims;
        dlg.setTitle(title);
        tk = Toolkit.getDefaultToolkit();
        screenDims = tk.getScreenSize();
        dlg.setLocation((screenDims.width - dlg.getWidth()) / 2, (screenDims.height - dlg.getHeight()) / 2);
        dlg.pack();
        dlg.setModalityType(JDialog.DEFAULT_MODALITY_TYPE);
        dlg.setDefaultCloseOperation(JDialog.DISPOSE_ON_CLOSE);
        dlg.setVisible(true);
    }
}