使用自定义的类作为HashMap的key【代码演示】

package com.Keafmd.April.test;
import java.util.HashMap;
/**
 * Keafmd
 *
 * @ClassName: TestHashMap
 * @Description:
 * @author: 牛哄哄的柯南
 * @Date: 2021-04-21 14:37
 * @Blog: https://keafmd.blog.csdn.net/
 */
public class TestHashMap {
    public static void main(String[] args) {
        /*HashMap<Integer,String> hashMap = new HashMap<>();
        hashMap.put(1,"hello");
        hashMap.put(2,"hello2");
        hashMap.forEach((key,value)->{
            System.out.println(key+" == "+value);
        });*/
        HashMap<Person, String> map = new HashMap<Person, String>();
        map.put(new Person("keafmd"), "6666");
        map.put(new Person("keafod"), "8888");
        map.put(new Person("keafod"), "9999"); // 这样就会覆盖掉8888
        System.out.println(map.toString());
        System.out.println("===============");
        System.out.println(map.get((new Person("keafmd"))));
        System.out.println(map.get((new Person("keafod"))));
        System.out.println("===============");
        System.out.println(new String("keafmd").hashCode());
        System.out.println("keafmd".hashCode());
        System.out.println(map.get("keafmd"));
        System.out.println("===============");
        map.forEach((key, value) -> {
            System.out.println(key.toString() + ".hashCode() = " + key.hashCode());
            System.out.println(key + ".value = " + value);
        });
    }
}
class Person {
    private String name;
    Person(String name) {
        this.name = name;
    }
    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj == null || getClass() != obj.getClass()) return false;
        Person person = (Person) obj;
        if (name != null ? !name.equals(person.name) : person.name != null) return false;
        return true;
    }
    @Override
    public int hashCode() {
        int result = 17;
        return 31 * result + name.hashCode();
        // 这样写的话，字符串"keafmd" 和 new Person("keafmd") 的哈希值就是一样的,
//        return name != null ? name.hashCode() : 0;
    }
    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                '}';
    }
}

{Person{name='keafod'}=9999, Person{name='keafmd'}=6666}
===============
6666
9999
===============
-1135381290
-1135381290
null
===============
Person{name='keafod'}.hashCode() = -1135380701
Person{name='keafod'}.value = 9999
Person{name='keafmd'}.hashCode() = -1135380763
Person{name='keafmd'}.value = 6666
Process finished with exit code 0