java中map插入相同的key

测试用例：

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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));       } }

　　

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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;     } }