同一个世界

请修改编辑器中的代码，完成一个图形界面程序，实现点击按钮切换背景色并绘制居中文本的功能，具体要求如下：创建一个窗口，标题为“北京 2008”，大小为 400×250 窗口中包含三个按钮：“Yellow”、“Blue”、“Green” 点击任意按钮，将窗口背景颜色切换为对应颜色在窗口中央绘制一行中文文本：“同一个世界，同一个梦想！” 使用字体“隶书”，加粗，字号为 27，文本颜色为红色文本应始终居中显示，不随按钮变化而消失所有绘图逻辑放在自定义的 JPanel 类中完成运行后弹出窗口，界面行为见代码注释；所有绘图逻辑写在自定义的 JPanel 子类中，文字始终居中显示。说明：本题是图形界面程序，运行后会弹出窗口，控制台上不会有输出。评测按填入的代码文本判分，不比对运行结果。

import java.awt.event.*;
import java.awt.*;
import java.awt.font.*;
import java.awt.geom.*;
import javax.swing.*;

public class Main
{
   public static void main(String[] args)
   {
      FontFrame frame = new FontFrame();
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.setVisible(true);
   }
}
class FontFrame extends ________________
{
   public FontFrame()
   {
      setTitle("北京 2008");
      setSize(DEFAULT_WIDTH, DEFAULT_HEIGHT);
      FontPanel panel = new FontPanel();
      Container contentPane = getContentPane();
      contentPane.add(_____________________);
   }
   public static final int DEFAULT_WIDTH = 400;
   public static final int DEFAULT_HEIGHT = 250;
}

class FontPanel extends JPanel
{
   public FontPanel()
   {
      JButton yellowButton = new JButton("Yellow");
      JButton blueButton = new JButton("Blue");
      JButton redButton = new JButton("Green");
      add(yellowButton);
      add(blueButton);
      add(redButton);
      ColorAction yellowAction = new ColorAction(Color.YELLOW);
      ColorAction blueAction = new ColorAction(Color.BLUE);
      ColorAction greenAction = new ColorAction(Color.GREEN);
      yellowButton.addActionListener(yellowAction);
      blueButton.addActionListener(blueAction);
      redButton.addActionListener(greenAction);
   }
   public void paintComponent(Graphics g)
   {
      super.paintComponent(g);
      Graphics2D g2 = (Graphics2D)g;
      String message = "同一个世界，同一个梦想！";
      Font f = new Font("隶书", Font.BOLD, 27);
      g2.setFont(f);
      FontRenderContext context = g2.getFontRenderContext();
      Rectangle2D bounds = f.getStringBounds(message, context);
      double x = (getWidth() - bounds.getWidth()) / 2;
      double y = (getHeight() - bounds.getHeight()) / 2;
      double ascent = -bounds.getY();
      double baseY = y + ascent;
      g2.setPaint(Color.RED);
      g2.drawString (message, (int)x, (int)(baseY));
   }
   private class ColorAction ____________________ ActionListener
   {
      public ColorAction(Color c)
      {
         BackgroundColor = c;
      }
      public void _____________________ (ActionEvent event)
      {
         setBackground(BackgroundColor);
      }
      private Color BackgroundColor;
   }
}

控制台

调试终端