1.图>>让LayoutManager像JPanel一样工作,JLabel返回Size(0,0)

第2位.图>>将一些PreferredSize添加到JLabel

3.图>>从添加到JLabel的JComponent计算的PreferredSize

4.图>>让LayoutManager将JLabel改为JPanel,现在LayoutManager正确计算了Dimension而不使用任何XxxSize

注意到使用了Nimbus L& F,所有可访问的L& F都有相同的输出

import java.awt.*;
import java.awt.event.*;
import java.util.LinkedList;
import java.util.Queue;
import javax.swing.*;
 
public class NimbusBorderPainterDemo extends JFrame {
 
    private static final long serialVersionUID = 1L;
    private JFrame frame = new JFrame();
    private JPanel fatherPanel = new JPanel(),titlePanel = new JPanel();
    private JLabel buttonPanel = new JLabel();
 
 
    //figure  ---> 4th. switch JLabel with JPanel
    //private JPanel buttonPanel = new JPanel();
    private Queue<Icon> iconQueue = new LinkedList<Icon>();
 
    public NimbusBorderPainterDemo() {
        iconQueue.add(UIManager.getIcon("OptionPane.errorIcon"));
        iconQueue.add(UIManager.getIcon("OptionPane.informationIcon"));
        iconQueue.add(UIManager.getIcon("OptionPane.warningIcon"));
        JButton button0 = createButton();
        JButton button1 = createButton();
        JButton button2 = createButton();
        button2.addActionListener(new ActionListener() {
 
            public void actionPerformed(ActionEvent e) {
                System.exit(1);
            }
        });
        int gap = 5;
        buttonPanel.setLayout(new GridLayout(0,3,gap,0));
        buttonPanel.add(button0);
        buttonPanel.add(button1);
        buttonPanel.add(button2);
 
        // figure 1st. --->  without PreferredSize
 
        // figure 2nd. --->
        //buttonPanel.setPreferredSize(new Dimension(160,30));
 
        // figure 3rd. --->
        /*Dimension dim = button0.getPreferredSize();
        int w = dim.width;
        int h = dim.height;
        w = (w + 5) * 3;
        h += 4;
        dim = new Dimension(w,h);
        buttonPanel.setPreferredSize(dim);*/
 
        titlePanel.setLayout(new BorderLayout());
        titlePanel.add(new JLabel(nextIcon()),BorderLayout.WEST);
        titlePanel.add(new JLabel("My Frame"),BorderLayout.CENTER);
        titlePanel.setBorder(BorderFactory.createLineBorder(Color.GRAY));
        titlePanel.add(buttonPanel,BorderLayout.EAST);
        fatherPanel.setLayout(new BorderLayout());
        fatherPanel.add(titlePanel,BorderLayout.CENTER);
        frame.setUndecorated(true);
        frame.add(fatherPanel);
        frame.setLocation(50,50);
        frame.pack();
        frame.setDefaultCloSEOperation(JFrame.DO_NOTHING_ON_CLOSE);
        frame.setVisible(true);
    }
 
    private JButton createButton() {
        JButton button = new JButton();
        button.setBorderPainted(false);
        button.setBorder(null);
        button.setFocusable(false);
        button.setMargin(new Insets(0,0));
        button.setContentAreaFilled(false);
        button.setIcon(nextIcon());
        //button.setRolloverIcon(nextIcon());
        //button.setPressedIcon(nextIcon());
        //button.setDisabledIcon(nextIcon());
        nextIcon();
        return button;
    }
 
    private Icon nextIcon() {
        Icon icon = iconQueue.peek();
        iconQueue.add(iconQueue.remove());
        return icon;
    }
 
    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
 
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel("com.sun.java.swing.plaf.nimbus.NimbusLookAndFeel");
                } catch (Exception fail) {
                }
                UIManager.getLookAndFeelDefaults().put("nimbusFocus",Color.RED);
                NimbusBorderPainterDemo nimbusBorderPainterDemo = new NimbusBorderPainterDemo();
            }
        });
    }
}