java中map插入相同的key

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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;    }}

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