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Java Swing - 如何在JFrame上動(dòng)態(tài)更改JPanels

我們想知道如何在JFrame上動(dòng)態(tài)更改JPanels。 
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class Main extends JFrame {
  private JPanel childPanel1 = new JPanel();
  private JPanel childPanel2 = new JPanel();
  private JPanel childPanel3 = new JPanel();

  public Main() {
    childPanel1.setBackground(Color.red);
    childPanel1.setPreferredSize(new Dimension(300, 40));
    childPanel2.setBackground(Color.blue);
    childPanel2.setPreferredSize(new Dimension(300, 40));
    childPanel3.setBackground(Color.yellow);
    childPanel3.setPreferredSize(new Dimension(300, 40));

    JButton myButton = new JButton("Add Component ");
    myButton.addActionListener(e -> {
      add(childPanel2, BorderLayout.CENTER);
      pack();
    });
    setLocation(10, 200);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    add(childPanel3, BorderLayout.CENTER);
    add(myButton, BorderLayout.SOUTH);
    pack();
    setVisible(true);
  }

  public static void main(String[] args) {
    Main Main = new Main();
  }
}