java中map插入相同的key

测试用例：

package test;

import org.junit.Test;
import po.Person;

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

/**
 * Created by Administrator on 2015/9/16.
 */
public class TestMap {
    /**
     * map插入相同key问题，value会不会覆盖
     */
    @Test
    public void testMap(){
        //HashMap中key的内容相同，则覆盖
        Map<String,Object> map1 = new HashMap<>();
        map1.put("张三",1);
        map1.put("张三",2);
        map1.put(new String("张三"),3);  //根据String特性，这三条内容相同，前两条地址相同
        map1.put("李四", 4);
        for (String s : map1.keySet()) {
            System.out.println(s+"======"+map1.get(s));
        }
        /** 结果
         *   张三======3
             李四======4
         */

        System.out.println("=====================================");
        //IdentityHashMap中key的内存地址必须完全相同才会覆盖
        Map<String,Object> map2 = new IdentityHashMap<>();
        map2.put("张三",1);
        map2.put("张三",2);
        map2.put(new String("张三"),3);//
        map2.put("李四", 4);
        for (String s : map2.keySet()) {
            System.out.println(s+"===="+map2.get(s));
        }
        /**
         * 李四====4
         张三====2
         张三====3
         */

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

        Map<Person,Object> map3 = new IdentityHashMap<>();
        map3.put(new Person("张三", 11), 1);
        map3.put(new Person("张三", 11), 3);
        map3.put(new Person("李四", 11), 4);
        for (Person s : map3.keySet()) {
            System.out.println(s.toString()+"===="+map3.get(s));
        }
        /**
         * po.Person@165474cf====1
         po.Person@3ff2caf4====4
         po.Person@2c0cd7d====3
         */
        System.out.println("=====================================");
        Person person = new Person("张三", 11);
        Person person2 = new Person("张三", 11);
        System.out.println(person.equals(person2));

    }
}

　　

package po;

/**
 * Created by Administrator on 2015/9/16.
 */
public class Person {
    int id;
    String name;
    int age;

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

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        Person person = (Person) o;

        if (id != person.id) return false;
        if (age != person.age) return false;
        return !(name != null ? !name.equals(person.name) : person.name != null);

    }

    @Override
    public int hashCode() {
        int result = id;
        result = 31 * result + (name != null ? name.hashCode() : 0);
        result = 31 * result + age;
        return result;
    }

    public Person(String name,int age){

        this.name=name;
        this.age=age;
    }
}