泛型初学者

package com.text10;

import java.util.*;

public class dome<T> {
    public static void main(String[] args) {
        DAO<User> dao = new DAO<User>();
        HashMap<String, User> map = new HashMap<>();
        dao.setMap(map);
        dao.save("哈哈",new User(12,23,"王"));
        dao.save("呵呵",new User(12,23,"文"));
        dao.save("嘿嘿",new User(12,23,"超"));

        dao.update("嘿嘿",new User(33,33,"牛"));
        dao.delete("嘿嘿");
        for(Map.Entry<String,User> en:dao.getMap().entrySet()){
             System.out.println(en);
        }

    }
}
class DAO<T>{
     private Map<String,T> map;

    public Map<String, T> getMap() {
        return map;
    }

    public void setMap(Map<String, T> map) {
        this.map = map;
    }

    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.put(id,entity);
    }
    public List<T> list(){
        ArrayList<T> list = new ArrayList<T>();
        for(String key : map.keySet()){
            list.add(map.get(key));
        }
        return list;
    }
    public void delete(String id){
            map.remove(id);
    }
}
class User {
    private int id;
    private  int age;
    private String name;

    public User() {
    }

    public int getId() {
        return id;
    }

    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 + '\'' +
                '}';
    }

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

    public int getAge() {
        return age;
    }

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

    public String getName() {
        return name;
    }

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