Map 自定义键时注意事项

public static void main(String[] args) {

        /*

         * 1.Map 的键是 String,Integer 等类的话，就会重写 HashCode () 和 equals () 方法，

         *   键的值一样，后面的就会覆盖前面的

         */

        Map<Integer,String> map1 = new HashMap<>();

        map1.put(0,"a");

        map1.put(1,"b");

        map1.put(2,"c");

        map1.put(2,"d");

        System.out.println(map1.toString());

        System.out.println("#####################");

        /*

         * 2. 键是自定义类的话，需要在自定义类中重写 HashCode () 和 equals () 方法，

         *   否则就算键的值一样，也会加进去的。

         */

        // 2.1 未定义了 hashcode 和 equals 的属性作为键

        Map<User,String> map2 = new HashMap<>();

        map2.put(new User("jalen","123456"),"a");

        map2.put(new User("abely","123456"),"b");

        map2.put(new User("mercy","123456"),"c");

        map2.put(new User("jermy","123456"),"d");

        map2.put(new User("jermy","123456"),"e");

        for(User user : map2.keySet())

        {

            System.out.println(user.toString()+":"+map2.get(user));

        }

        System.out.println("#####################");

        // 2.1 定义了 hashcode 和 equals 的属性作为键

        Map<Manager,String> map3 = new HashMap<>();

        map3.put(new Manager("jalen","123456"),"aa");

        map3.put(new Manager("abely","123456"),"bb");

        map3.put(new Manager("mercy","123456"),"cc");

        map3.put(new Manager("jermy","123456"),"dd");

        map3.put(new Manager("jermy","123456"),"ee");

        for (Manager manager: map3.keySet()) {

            System.out.println(manager.toString()+":"+map3.get(manager));

        }

    }

import lombok.AllArgsConstructor;

import lombok.ToString;

@AllArgsConstructor

@ToString

public class User {

    private String username;

    private String password;

}

import lombok.Data;

import lombok.NoArgsConstructor;

@Data

@AllArgsConstructor

@NoArgsConstructor

public class Manager {

    private String managerName;

    private String managerPassword;

}