Java 小例子：猜数字游戏

这是一个猜数字的游戏。用户输入 1~1000 以内的任意数字，程序给出它是大了还是小了，直到猜出正确的结果。

import javax.swing.*;
import java.awt.BorderLayout;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import java.util.Random;

/**
 * 猜数字
 */
public class GuessNumber extends JFrame {

    private Random r = new Random();

    private int result = r.nextInt(1000) + 1;

    private int counter = 0;

    private boolean finished = false;

    private GuessNumber thisFrame = this;

    private ActionListener guessButtonListener = new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            if (!finished) {
                String user_guess = textbox.getText();
                if (user_guess.length() == 0) {
                    messageLabel.setText("输入文本不能为空。");
                } else {
                    try {
                        int guess = Integer.parseInt(user_guess);
                        counter++;

                        if (guess < result) {
                            messageLabel.setText("你输入的数字 " + guess + " 比结果小。");
                        } else if (guess > result) {
                            messageLabel.setText("你输入的数字 " + guess + " 比结果大。");
                        } else {
                            finished = true;
                            messageLabel.setText("OK，经过" + counter + "次猜测，你终于猜中了。");
                            button.setText("再来一次");
                        }
                    } catch (NumberFormatException e1) {
                        messageLabel.setText("请输入数字。");
                    }
                }
            } else {
                result = r.nextInt(1000) + 1;
                counter = 0;
                finished = false;
                messageLabel.setText("请输入一个 1~1000 之内的数字。");
                button.setText("猜一猜");
                thisFrame.setTitle(String.valueOf(result));
            }
        }
    };

    private JTextField textbox = new JTextField();

    private JLabel messageLabel = new JLabel("请输入一个 1~1000 之内的数字。");

    private JButton button = new JButton("猜一猜");

    public static void main(String[] args) {
        GuessNumber frame = new GuessNumber();
        frame.setVisible(true);
    }

    public GuessNumber() {
        super("猜数字");
        this.setDefaultCloseOperation(EXIT_ON_CLOSE);
        this.setSize(400, 200);
        this.setLocation(200, 200);
        this.setResizable(false);

        setupContentPane();
        setupControls();
        this.setTitle(String.valueOf(result));
    }

    private void setupContentPane() {
        JPanel contentPane = new JPanel(new BorderLayout());
        contentPane.setBorder(BorderFactory.createEmptyBorder(5, 5, 5, 5));
        this.setContentPane(contentPane);
    }

    private void setupControls() {
        JPanel topPanel = new JPanel(new BorderLayout());
        setupTupPanel(topPanel);
        this.add(topPanel, BorderLayout.NORTH);
        this.add(messageLabel, BorderLayout.CENTER);
    }

    private void setupTupPanel(JPanel panel) {
        panel.add(textbox, BorderLayout.CENTER);
        button.addActionListener(guessButtonListener);
        panel.add(button, BorderLayout.EAST);
    }
}