4. Java 员工管理系统 员工属性：员工编号、员工姓名、性别、年龄、所在部门 1————员工添加 2- 3- 4- 5 -一员工删除 —一员工信息修改 -—根据员工编号查询员工信息 - 查询所有员工信息

以下是一个简单的 Java 员工管理系统，实现了员工添加、删除、修改和查询功能。

import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class EmployeeManagementSystem {
    private static List<Employee> employees = new ArrayList<>();

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        while (true) {
            System.out.println("请选择操作：");
            System.out.println("1. 员工添加");
            System.out.println("2. 员工删除");
            System.out.println("3. 员工信息修改");
            System.out.println("4. 根据员工编号查询员工信息");
            System.out.println("5. 查询所有员工信息");

            int choice = scanner.nextInt();
            switch (choice) {
                case 1:
                    addEmployee(scanner);
                    break;
                case 2:
                    deleteEmployee(scanner);
                    break;
                case 3:
                    updateEmployee(scanner);
                    break;
                case 4:
                    queryEmployeeById(scanner);
                    break;
                case 5:
                    queryAllEmployees();
                    break;
                default:
                    System.out.println("无效的选择！");
                    break;
            }
        }
    }

    private static void addEmployee(Scanner scanner) {
        System.out.println("请输入员工编号：");
        int id = scanner.nextInt();
        scanner.nextLine(); // 读取换行符
        System.out.println("请输入员工姓名：");
        String name = scanner.nextLine();
        System.out.println("请输入员工性别：");
        String gender = scanner.nextLine();
        System.out.println("请输入员工年龄：");
        int age = scanner.nextInt();
        scanner.nextLine(); // 读取换行符
        System.out.println("请输入员工所在部门：");
        String department = scanner.nextLine();
        Employee employee = new Employee(id, name, gender, age, department);
        employees.add(employee);
        System.out.println("员工添加成功！");
    }

    private static void deleteEmployee(Scanner scanner) {
        System.out.println("请输入员工编号：");
        int id = scanner.nextInt();
        boolean found = false;
        for (Employee employee : employees) {
            if (employee.getId() == id) {
                employees.remove(employee);
                found = true;
                break;
            }
        }
        if (found) {
            System.out.println("员工删除成功！");
        } else {
            System.out.println("未找到该员工！");
        }
    }

    private static void updateEmployee(Scanner scanner) {
        System.out.println("请输入员工编号：");
        int id = scanner.nextInt();
        boolean found = false;
        for (Employee employee : employees) {
            if (employee.getId() == id) {
                scanner.nextLine(); // 读取换行符
                System.out.println("请输入员工姓名（原值：" + employee.getName() + "）：");
                String name = scanner.nextLine();
                System.out.println("请输入员工性别（原值：" + employee.getGender() + "）：");
                String gender = scanner.nextLine();
                System.out.println("请输入员工年龄（原值：" + employee.getAge() + "）：");
                int age = scanner.nextInt();
                scanner.nextLine(); // 读取换行符
                System.out.println("请输入员工所在部门（原值：" + employee.getDepartment() + "）：");
                String department = scanner.nextLine();
                employee.setName(name);
                employee.setGender(gender);
                employee.setAge(age);
                employee.setDepartment(department);
                found = true;
                break;
            }
        }
        if (found) {
            System.out.println("员工信息修改成功！");
        } else {
            System.out.println("未找到该员工！");
        }
    }

    private static void queryEmployeeById(Scanner scanner) {
        System.out.println("请输入员工编号：");
        int id = scanner.nextInt();
        boolean found = false;
        for (Employee employee : employees) {
            if (employee.getId() == id) {
                System.out.println(employee);
                found = true;
                break;
            }
        }
        if (!found) {
            System.out.println("未找到该员工！");
        }
    }

    private static void queryAllEmployees() {
        for (Employee employee : employees) {
            System.out.println(employee);
        }
    }
}

class Employee {
    private int id;
    private String name;
    private String gender;
    private int age;
    private String department;

    public Employee(int id, String name, String gender, int age, String department) {
        this.id = id;
        this.name = name;
        this.gender = gender;
        this.age = age;
        this.department = department;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public String getDepartment() {
        return department;
    }

    public void setDepartment(String department) {
        this.department = department;
    }

    @Override
    public String toString() {
        return "Employee{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", gender='" + gender + '\'' +
                ", age=" + age +
                ", department='" + department + '\'' +
                '}';
    }
}

这个程序通过一个 `List<Employee>` 来保存所有员工的信息，每个员工由员工编号、员工姓名、性别、年龄和所在部门五个属性组成。在主函数中，程序通过读取用户输入的选项来执行相应的操作：

- 员工添加：读取用户输入的员工信息，创建一个新的 `Employee` 对象并添加到 `employees` 列表中。
- 员工删除：读取用户输入的员工编号，遍历 `employees` 列表寻找该员工，如果找到则从列表中删除。
- 员工信息修改：读取用户输入的员工编号，遍历 `employees` 列表寻找该员工，如果找到则读取用户输入的新员工信息并更新该员工的属性。
- 根据员工编号查询员工信息：读取用户输入的员工编号，遍历 `employees` 列表寻找该员工，如果找到则打印该员工的信息。
- 查询所有员工信息：遍历 `employees` 列表打印所有员工的信息。

这个程序比较简单，没有做输入校验等复杂的处理，但足以演示 Java 中如何实现一个员工管理系统。