1．实现一个窗体，要求：(1）标题显示： GUI 实验；(2）窗体尺寸为：长400像素，宽300像素，窗体左上角坐标位置为（150,100)，分别使用 Dimension 类和 Point 类实现； (3）窗体内通过标签控件显示国旗图标和文字内容：中华人民共和国 字体为：幼圆字体，20号，红色，加粗，倾斜。1．仿照 window 计算器，实现计算器界面。 2．使用绝对定位，实现注册和登录界面。

实现一个窗体：

import java.awt.Dimension;
import java.awt.Font;
import java.awt.Point;

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.ImageIcon;

public class MyFrame extends JFrame {

    public MyFrame() {
        this.setTitle("GUI 实验");
        this.setSize(new Dimension(400, 300));
        this.setLocation(new Point(150, 100));
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JLabel label = new JLabel("中华人民共和国", new ImageIcon("china.png"), JLabel.CENTER);
        label.setFont(new Font("幼圆", Font.BOLD + Font.ITALIC, 20));
        label.setForeground(Color.RED);
        this.add(label);
    }

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

}

实现一个计算器界面：

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

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

public class Calculator extends JFrame implements ActionListener {

    private JTextField textField;

    private double firstNumber, secondNumber;
    private String operator;

    public Calculator() {
        this.setTitle("计算器");
        this.setSize(300, 400);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JPanel panel = new JPanel();
        panel.setLayout(new GridLayout(4, 4, 5, 5));
        String[] buttonLabels = { "7", "8", "9", "/", "4", "5", "6", "*", "1", "2", "3", "-", "0", ".", "=", "+" };
        JButton[] buttons = new JButton[buttonLabels.length];
        for (int i = 0; i < buttons.length; i++) {
            buttons[i] = new JButton(buttonLabels[i]);
            buttons[i].addActionListener(this);
            panel.add(buttons[i]);
        }

        textField = new JTextField();
        textField.setEditable(false);
        textField.setBackground(Color.WHITE);

        this.add(textField, BorderLayout.NORTH);
        this.add(panel, BorderLayout.CENTER);
    }

    public void actionPerformed(ActionEvent e) {
        String command = e.getActionCommand();
        if (command.matches("\\d")) {
            textField.setText(textField.getText() + command);
        } else if (command.matches("[+\\-*/]")) {
            firstNumber = Double.parseDouble(textField.getText());
            operator = command;
            textField.setText("");
        } else if (command.equals(".")) {
            if (!textField.getText().contains(".")) {
                textField.setText(textField.getText() + command);
            }
        } else if (command.equals("=")) {
            secondNumber = Double.parseDouble(textField.getText());
            double result = 0;
            switch (operator) {
            case "+":
                result = firstNumber + secondNumber;
                break;
            case "-":
                result = firstNumber - secondNumber;
                break;
            case "*":
                result = firstNumber * secondNumber;
                break;
            case "/":
                result = firstNumber / secondNumber;
                break;
            }
            textField.setText(String.valueOf(result));
        } else if (command.equals("C")) {
            textField.setText("");
        }
    }

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

}

使用绝对定位，实现注册和登录界面：

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JPasswordField;
import javax.swing.JTextField;

public class Login extends JFrame implements ActionListener {

    private static final int WIDTH = 400;
    private static final int HEIGHT = 300;

    private JTextField usernameField;
    private JPasswordField passwordField;

    public Login() {
        this.setTitle("登录");
        this.setSize(WIDTH, HEIGHT);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
        int x = (screenSize.width - WIDTH) / 2;
        int y = (screenSize.height - HEIGHT) / 2;
        this.setLocation(x, y);

        JPanel panel = new JPanel(null);

        JLabel titleLabel = new JLabel("欢迎使用我的系统");
        titleLabel.setFont(new Font("微软雅黑", Font.BOLD, 20));
        titleLabel.setForeground(Color.BLUE);
        titleLabel.setBounds(120, 30, 200, 30);
        panel.add(titleLabel);

        JLabel usernameLabel = new JLabel("用户名：");
        usernameLabel.setFont(new Font("微软雅黑", Font.PLAIN, 16));
        usernameLabel.setBounds(80, 80, 80, 30);
        panel.add(usernameLabel);

        usernameField = new JTextField();
        usernameField.setBounds(150, 80, 150, 30);
        panel.add(usernameField);

        JLabel passwordLabel = new JLabel("密  码：");
        passwordLabel.setFont(new Font("微软雅黑", Font.PLAIN, 16));
        passwordLabel.setBounds(80, 120, 80, 30);
        panel.add(passwordLabel);

        passwordField = new JPasswordField();
        passwordField.setBounds(150, 120, 150, 30);
        panel.add(passwordField);

        JButton loginButton = new JButton("登录");
        loginButton.setBounds(100, 180, 80, 30);
        loginButton.addActionListener(this);
        panel.add(loginButton);

        JButton registerButton = new JButton("注册");
        registerButton.setBounds(220, 180, 80, 30);
        registerButton.addActionListener(this);
        panel.add(registerButton);

        this.setContentPane(panel);
    }

    public void actionPerformed(ActionEvent e) {
        String command = e.getActionCommand();
        if (command.equals("登录")) {
            String username = usernameField.getText();
            String password = new String(passwordField.getPassword());
            if (username.equals("admin") && password.equals("admin")) {
                System.out.println("登录成功！");
            } else {
                System.out.println("用户名或密码错误！");
            }
        } else if (command.equals("注册")) {
            System.out.println("进入注册页面！");
        }
    }

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

}