Java泛型类编程测试

package com.joshua317;

import java.util.*;

/**
 * 编程要求：
 * 1.定义一个泛型类Dao<T>，在其中定义一个map成员变量，map的键为string类型，值为T类型
 * (1)public void save(String id, T entity),保存T类型对象到map成员变量中
 * (2)public T get(String id),从map中获取id对应的T对象
 * (3)public void update(String id, T entity),更新map中key为id的对象，内容为T对象entity
 * (4)public List<T> list(),返回map中存放的所有T对象
 * (5)public void delete(String id)，删除map中指定key为id的对象
 * 2.定义一个User类，设置三个私有属性，分别为int id,int age,String name;重写toString方法，显示属性信息
 * 3.创建Dao类对象，分别调用Dao类的成员方法来操作User对象
 * 4.使用Junit单元类进行单元测试
 */
public class Main {
    public static void main(String[] args) {
        Dao<User> userDao = new Dao<>();
        User user1 = new User(1, 2, "red");
        User user2 = new User(2, 3, "yellow");
        User user3 = new User(3, 5, "blue");
        userDao.save("001", user1);
        userDao.save("002", user2);
        userDao.save("003", user3);

        System.out.println(userDao.get("002"));

        System.out.println(userDao.list());

        userDao.delete("003");
        System.out.println(userDao.list());

        user2 = new User(2, 3, "purple");
        userDao.update("002",user2);
        System.out.println(userDao.list());
    }
}

class Dao<T> {
    Map<String,T> map = new HashMap<>();

    public void save(String id, T entity)
    {
        map.put(id, entity);
    }
    public T get(String id)
    {
        return map.get(id);
    }
    public void update(String id, T entity)
    {
        map.replace(id, entity);
    }
    public List<T> list()
    {
        ArrayList<T> arrayList = new ArrayList<>();
        Set<String> keys = map.keySet();
        for (String key: keys) {
            arrayList.add(map.get(key));
        }
        return arrayList;
    }
    public void delete(String id)
    {
        map.remove(id);
    }
}

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

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

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