import javax.swing.*;
import java.awt.*;

public class BoxPanel extends JPanel{
               
       public BoxPanel(){
               
             setLayout(new BoxLayout(this,BoxLayout.Y_AXIS));   
             setBackground(Color.gray);
            
             JButton b1=new JButton("Button 1");
             JButton b2=new JButton("Button 2");
             JButton b3=new JButton("Button 3");
             JButton b4=new JButton("Button 4");
             JButton b5=new JButton("Button 5");
            
            
            
             add(b1);
             add(Box.createRigidArea(new Dimension(0, 15)));
             add(b2);
             add(Box.createVerticalGlue());
             add(b3);
             add(b4);
             add(Box.createRigidArea(new Dimension(0,20)));
             add(b5);
            
            
       }   
}


之后编译发现有问题  
.\BoxPanel.java:20: 错误: 找不到符号
             add(Box.createRigidArea(new Dimension(0, 15)));
                    ^
  符号:   方法 createRigidArea(Dimension)
  位置: 类 Box
.\BoxPanel.java:22: 错误: 找不到符号
             add(Box.createVerticalGlue());
                    ^
  符号:   方法 createVerticalGlue()
  位置: 类 Box
.\BoxPanel.java:25: 错误: 找不到符号
             add(Box.createRigidArea(new Dimension(0,20)));
                    ^
  符号:   方法 createRigidArea(Dimension)
  位置: 类 Box
3 个错误

import javax.swing.*;

public class LayoutDemo {

       public static void main(String[] args){
           
            JFrame frame=new JFrame("Layout");
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            
            JTabbedPane tb=new JTabbedPane();
            // tb.add("Intro",new IntroPanel());   
            //tb.add("Flow",new FlowPanel());   
            //tb.add("Border",new BorderPanel());   
            //tb.add("Grid",new GridPanel());   
            tb.add("Box",new BoxPanel());   
            
            frame.getContentPane().add(tb);
            frame.pack();
            frame.setVisible(true);
       }
}
import javax.swing.*;
import java.awt.*;
public class BoxPanel extends JPanel{
               private JPanel panel;
       public BoxPanel(){
               
             setLayout(new BoxLayout(this,BoxLayout.Y_AXIS));   
             setBackground(Color.gray);
            
             JButton b1=new JButton("Button 1");
             JButton b2=new JButton("Button 2");
             JButton b3=new JButton("Button 3");
             JButton b4=new JButton("Button 4");
             JButton b5=new JButton("Button 5");
            
            
            
             add(b1);
             //add(Box.createRigidArea(new Dimension(0, 15)));
             add(b2);
             //add(Box.createVerticalGlue());
             add(b3);
             add(b4);
             //add(Box.createRigidArea(new Dimension(0,20)));
             add(b5);
            
            
       }   
}
我把下面三条注释了  可以运行 不注释的话就出现说找不到符号的问题

谢谢  需要import javax.swing.Box;

看来还是不细心