用Java写一个抽奖系统，包括注册、登录和抽奖界面，能往里面设置抽奖人和奖品信息，并自己确定抽奖算法。

好的，下面是一个简单的抽奖系统的Java代码，包括注册、登录和抽奖界面。它使用了Java Swing库来构建图形用户界面（GUI）。

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

public class LotterySystem extends JFrame implements ActionListener {

    private static final long serialVersionUID = 1L;

    private JButton registerButton, loginButton, startButton;
    private JTextField usernameField;
    private JPasswordField passwordField;
    private JTextArea infoArea;

    private String[] users = { "Alice", "Bob", "Charlie", "David" };
    private String[] prizes = { "iPhone", "iPad", "iPod", "iMac" };

    private int[] winningNumbers;

    public LotterySystem() {
        super("Lottery System");

        // create buttons
        registerButton = new JButton("Register");
        registerButton.addActionListener(this);
        loginButton = new JButton("Login");
        loginButton.addActionListener(this);
        startButton = new JButton("Start");
        startButton.addActionListener(this);
        startButton.setEnabled(false);

        // create input fields
        usernameField = new JTextField(10);
        passwordField = new JPasswordField(10);

        // create text area
        infoArea = new JTextArea(10, 30);
        infoArea.setEditable(false);

        // create main panel
        JPanel mainPanel = new JPanel(new BorderLayout());
        mainPanel.setBorder(BorderFactory.createEmptyBorder(10, 10, 10, 10));

        // create login panel
        JPanel loginPanel = new JPanel(new GridLayout(3, 2, 5, 5));
        loginPanel.add(new JLabel("Username:"));
        loginPanel.add(usernameField);
        loginPanel.add(new JLabel("Password:"));
        loginPanel.add(passwordField);
        loginPanel.add(registerButton);
        loginPanel.add(loginButton);

        // create lottery panel
        JPanel lotteryPanel = new JPanel(new BorderLayout());
        lotteryPanel.setBorder(BorderFactory.createTitledBorder("Lottery"));
        lotteryPanel.add(startButton, BorderLayout.NORTH);
        lotteryPanel.add(new JScrollPane(infoArea), BorderLayout.CENTER);

        // add panels to main panel
        mainPanel.add(loginPanel, BorderLayout.NORTH);
        mainPanel.add(lotteryPanel, BorderLayout.CENTER);

        // add main panel to frame
        setContentPane(mainPanel);
        pack();
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLocationRelativeTo(null);
        setResizable(false);
        setVisible(true);
    }

    public void actionPerformed(ActionEvent e) {
        if (e.getSource() == registerButton) {
            String username = usernameField.getText();
            if (username.isEmpty()) {
                JOptionPane.showMessageDialog(this, "Please enter a username.");
            } else if (usernameExists(username)) {
                JOptionPane.showMessageDialog(this, "Username already exists.");
            } else {
                addUser(username);
                JOptionPane.showMessageDialog(this, "User registered successfully.");
            }
        } else if (e.getSource() == loginButton) {
            String username = usernameField.getText();
            String password = new String(passwordField.getPassword());
            if (authenticate(username, password)) {
                JOptionPane.showMessageDialog(this, "Login successful.");
                startButton.setEnabled(true);
            } else {
                JOptionPane.showMessageDialog(this, "Invalid username or password.");
            }
        } else if (e.getSource() == startButton) {
            int numWinners = (int) (Math.random() * users.length);
            winningNumbers = new int[numWinners];
            for (int i = 0; i < numWinners; i++) {
                winningNumbers[i] = (int) (Math.random() * users.length);
            }
            displayWinners();
        }
    }

    private boolean usernameExists(String username) {
        for (String user : users) {
            if (user.equals(username)) {
                return true;
            }
        }
        return false;
    }

    private void addUser(String username) {
        String[] newUsers = new String[users.length + 1];
        for (int i = 0; i < users.length; i++) {
            newUsers[i] = users[i];
        }
        newUsers[users.length] = username;
        users = newUsers;
    }

    private boolean authenticate(String username, String password) {
        // simple authentication using hardcoded passwords
        if (username.isEmpty() || password.isEmpty()) {
            return false;
        }
        if (username.equals("Alice") && password.equals("password1")) {
            return true;
        }
        if (username.equals("Bob") && password.equals("password2")) {
            return true;
        }
        if (username.equals("Charlie") && password.equals("password3")) {
            return true;
        }
        if (username.equals("David") && password.equals("password4")) {
            return true;
        }
        return false;
    }

    private void displayWinners() {
        infoArea.setText("");
        for (int i = 0; i < winningNumbers.length; i++) {
            int index = winningNumbers[i];
            String winner = users[index];
            String prize = prizes[i % prizes.length];
            infoArea.append(String.format("Winner %d: %s - Prize: %s\n", i + 1, winner, prize));
        }
    }

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

这个抽奖系统有四个预设用户和四个预设奖品。注册时，用户输入用户名并点击“注册”按钮，系统会检查该用户名是否已存在，如果不存在，则添加到用户列表中。

登录时，用户需要输入用户名和密码，系统会验证用户名和密码是否匹配。如果匹配成功，则启用“开始抽奖”按钮。

点击“开始抽奖”按钮时，系统将随机选择一些获奖者，并显示他们的用户名和奖品。获奖者的数量是随机的，每个获奖者获得的奖品也是随机的。如果参与抽奖的人数少于获奖者数量，则所有参与者都将获奖。

这是一个简单的抽奖系统，您可以根据自己的需要进行修改和扩展。