learning java AWT 布局管理器CardLayout

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

public class CardLayoutTest {
    Frame f = new Frame("cardlayout test");
    Panel p1 = new Panel();
    String[] names = {"上一张","下一张","第一张","最后一张","第三张"};

    public void init(){
        final var c =  new CardLayout();
        p1.setLayout(c);
        for(var i = 0; i < names.length; i++){
            p1.add(names[i], new JButton(names[i]));
        }
        var p  = new Panel();
        ActionListener listener = e -> {
            switch (e.getActionCommand()){
                case "上一张":
                    System.out.println("previous");
                    c.previous(p1);
                    break;
                case "下一张":
                    c.next(p1);
                    System.out.println("next");
                    break;
                case "第一张":
                    c.first(p1);
                    System.out.println("first");
                    break;
                case "最后一张":
                    c.last(p1);
                    System.out.println("last");
                    break;
                case "第三张":
                    c.show(p1, "第三张");
                    System.out.println("third");
                    break;
            }
        };

        var previous = new JButton("上一张");
        previous.addActionListener(listener);

        var next = new JButton("下一张");
        next.addActionListener(listener);

        var first = new JButton("第一张");
        first.addActionListener(listener);

        var last = new JButton("最后一张");
        last.addActionListener(listener);

        var third = new JButton("第三张");
        third.addActionListener(listener);

        p.add(previous);
        p.add(next);
        p.add(first);
        p.add(last);
        p.add(third);

        f.add(p1);
        f.add(p, BorderLayout.NORTH);
        f.setLocation(100,100);
        f.setBounds(100,100,300,500);
        f.pack();
        f.setVisible(true);

    }

    public static void main(String[] args) {
        new CardLayoutTest().init();
    }

}

output: