用java写一个网吧管理系统，写出源代码

好的，下面给出一个简单的网吧管理系统的Java代码，包括用户登录和设备管理功能。这里使用命令行界面进行交互，你可以根据需要修改代码，添加其他功能。

import java.util.Scanner;

public class CybercafeSystem {
    // 用户名和密码
    private static final String USERNAME = "admin";
    private static final String PASSWORD = "123456";

    // 设备数量
    private static final int NUM_COMPUTERS = 50;
    private static final int NUM_PRINTERS = 10;

    // 设备状态
    private static boolean[] computerStatus = new boolean[NUM_COMPUTERS];
    private static boolean[] printerStatus = new boolean[NUM_PRINTERS];

    public static void main(String[] args) {
        // 用户登录
        Scanner scanner = new Scanner(System.in);
        System.out.println("Welcome to Cybercafe System!");
        System.out.print("Please enter username: ");
        String username = scanner.nextLine();
        System.out.print("Please enter password: ");
        String password = scanner.nextLine();
        if (!username.equals(USERNAME) || !password.equals(PASSWORD)) {
            System.out.println("Invalid username or password!");
            return;
        }

        // 设备管理
        while (true) {
            System.out.println("Please select operation:");
            System.out.println("1. Computer Management");
            System.out.println("2. Printer Management");
            System.out.println("3. Exit");
            int operation = scanner.nextInt();
            if (operation == 3) {
                break;
            }
            switch (operation) {
                case 1:
                    computerManagement();
                    break;
                case 2:
                    printerManagement();
                    break;
                default:
                    System.out.println("Invalid operation!");
            }
        }
    }

    // 计算可用设备数量
    private static int getAvailableDevices(boolean[] devices) {
        int count = 0;
        for (boolean device : devices) {
            if (!device) {
                count++;
            }
        }
        return count;
    }

    // 计算已使用设备数量
    private static int getUsedDevices(boolean[] devices) {
        return devices.length - getAvailableDevices(devices);
    }

    // 计算设备利用率
    private static float getDeviceUtilization(boolean[] devices) {
        return (float) getUsedDevices(devices) / devices.length;
    }

    // 计算设备编号
    private static int getDeviceNumber(boolean[] devices) {
        for (int i = 0; i < devices.length; i++) {
            if (!devices[i]) {
                return i + 1;
            }
        }
        return -1;
    }

    // 计算设备状态
    private static String getDeviceStatus(boolean device) {
        if (device) {
            return "Occupied";
        } else {
            return "Available";
        }
    }

    // 设备管理 - 电脑
    private static void computerManagement() {
        Scanner scanner = new Scanner(System.in);
        while (true) {
            System.out.println("Computer Management:");
            System.out.println("1. Check Computer Status");
            System.out.println("2. Occupy a Computer");
            System.out.println("3. Release a Computer");
            System.out.println("4. Exit");
            int operation = scanner.nextInt();
            if (operation == 4) {
                break;
            }
            switch (operation) {
                case 1:
                    // 查询电脑状态
                    System.out.println("Computer Status:");
                    System.out.println("Total: " + NUM_COMPUTERS);
                    System.out.println("Available: " + getAvailableDevices(computerStatus));
                    System.out.println("Occupied: " + getUsedDevices(computerStatus));
                    System.out.println("Utilization: " + String.format("%.2f", getDeviceUtilization(computerStatus) * 100) + "%");
                    break;
                case 2:
                    // 占用电脑
                    int computerNumber = getDeviceNumber(computerStatus);
                    if (computerNumber == -1) {
                        System.out.println("No available computer!");
                    } else {
                        computerStatus[computerNumber - 1] = true;
                        System.out.println("Computer " + computerNumber + " has been occupied!");
                    }
                    break;
                case 3:
                    // 释放电脑
                    System.out.print("Please enter computer number: ");
                    computerNumber = scanner.nextInt();
                    if (computerNumber < 1 || computerNumber > NUM_COMPUTERS) {
                        System.out.println("Invalid computer number!");
                    } else if (!computerStatus[computerNumber - 1]) {
                        System.out.println("Computer " + computerNumber + " is already available!");
                    } else {
                        computerStatus[computerNumber - 1] = false;
                        System.out.println("Computer " + computerNumber + " has been released!");
                    }
                    break;
                default:
                    System.out.println("Invalid operation!");
            }
        }
    }

    // 设备管理 - 打印机
    private static void printerManagement() {
        Scanner scanner = new Scanner(System.in);
        while (true) {
            System.out.println("Printer Management:");
            System.out.println("1. Check Printer Status");
            System.out.println("2. Occupy a Printer");
            System.out.println("3. Release a Printer");
            System.out.println("4. Exit");
            int operation = scanner.nextInt();
            if (operation == 4) {
                break;
            }
            switch (operation) {
                case 1:
                    // 查询打印机状态
                    System.out.println("Printer Status:");
                    System.out.println("Total: " + NUM_PRINTERS);
                    System.out.println("Available: " + getAvailableDevices(printerStatus));
                    System.out.println("Occupied: " + getUsedDevices(printerStatus));
                    System.out.println("Utilization: " + String.format("%.2f", getDeviceUtilization(printerStatus) * 100) + "%");
                    break;
                case 2:
                    // 占用打印机
                    int printerNumber = getDeviceNumber(printerStatus);
                    if (printerNumber == -1) {
                        System.out.println("No available printer!");
                    } else {
                        printerStatus[printerNumber - 1] = true;
                        System.out.println("Printer " + printerNumber + " has been occupied!");
                    }
                    break;
                case 3:
                    // 释放打印机
                    System.out.print("Please enter printer number: ");
                    printerNumber = scanner.nextInt();
                    if (printerNumber < 1 || printerNumber > NUM_PRINTERS) {
                        System.out.println("Invalid printer number!");
                    } else if (!printerStatus[printerNumber - 1]) {
                        System.out.println("Printer " + printerNumber + " is already available!");
                    } else {
                        printerStatus[printerNumber - 1] = false;
                        System.out.println("Printer " + printerNumber + " has been released!");
                    }
                    break;
                default:
                    System.out.println("Invalid operation!");
            }
        }
    }
}

以上代码演示了一个简单的网吧管理系统，包括用户登录和设备管理功能。