用户管理系统：增加，删除，查找用户java代码

好的，下面是用户管理系统的Java代码示例：

User类：

public class User {
    private int id;
    private String name;
    private int age;
    private String gender;

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

    // getter and setter methods
}

UserDao接口：

public interface UserDao {
    void addUser(User user);

    void deleteUser(int userId);

    User findUserById(int userId);

    User findUserByName(String userName);
}

UserDao的实现类UserDaoImpl：

import java.util.HashMap;
import java.util.Map;

public class UserDaoImpl implements UserDao {
    private Map<Integer, User> users = new HashMap<>();
    private int id = 1;

    @Override
    public void addUser(User user) {
        user.setId(id++);
        users.put(user.getId(), user);
        System.out.println("User added successfully!");
    }

    @Override
    public void deleteUser(int userId) {
        User user = users.remove(userId);
        if (user != null) {
            System.out.println("User deleted successfully!");
        } else {
            System.out.println("User not found!");
        }
    }

    @Override
    public User findUserById(int userId) {
        User user = users.get(userId);
        if (user != null) {
            System.out.println("User found: " + user.getName());
        } else {
            System.out.println("User not found!");
        }
        return user;
    }

    @Override
    public User findUserByName(String userName) {
        for (User user : users.values()) {
            if (user.getName().equals(userName)) {
                System.out.println("User found: " + user.getName());
                return user;
            }
        }
        System.out.println("User not found!");
        return null;
    }
}

使用示例：

public static void main(String[] args) {
    UserDao userDao = new UserDaoImpl();

    // add user
    User user1 = new User(0, "Tom", 20, "Male");
    userDao.addUser(user1);

    // find user by id
    userDao.findUserById(1);

    // find user by name
    userDao.findUserByName("Tom");

    // delete user
    userDao.deleteUser(1);
}

输出：

User added successfully!
User found: Tom
User found: Tom
User deleted successfully!