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【第13章：Java类集】_IdentityHashMap类

发布时间：2021-01-03 17:17:51编辑：雪饮阅读（）

 正常Map操作中key是不可以重复的，若有重复就会有其中一个被覆盖掉。

import java.util.HashMap;
import java.util.Map;
import java.util.Set ;
import java.util.Iterator ;
class Person{
       private String name;
       private int age;
       public Person(String name,int age){
              this.name=name;
              this.age=age;
       }
       public String toString(){
              return "姓名:"+this.name+" 年龄:"+this.age;
       }
       public boolean equals(Object obj){
              if(obj==this){
                     return true;
              }
              if(!(obj instanceof Person)){
                     return false;
              }
              Person p=(Person)obj;
              if(p.name.equals(this.name) && p.age==this.age){
                     return true;
              }
              return false;
       }
       public int hashCode(){
              return this.name.hashCode()*this.age;
       }
}
public class TestJava{
       public static void main(String args[]){
              Map<Person,String> map=new HashMap<Person,String>();
              map.put(new Person("霞",24),"kasumi");
              map.put(new Person("霞",24),"momiji");
              Set<Map.Entry<Person,String>> allSet=map.entrySet();
              Iterator<Map.Entry<Person,String>> iter=allSet.iterator();
              while(iter.hasNext()){
                     Map.Entry<Person,String> me=iter.next();
                     System.out.println(me.getKey()+" --> "+me.getValue());
              }
       }
}

用IdentityHashMap类给Map进行实例化则允许key重复
那么用IdentityHashMap类来实现只需要导入该类然后替换上面的HashMap即可，其它地方都不需要修改，如：
import java.util.IdentityHashMap ;
import java.util.Map;
import java.util.Set ;
import java.util.Iterator ;
class Person{
       private String name;
       private int age;
       public Person(String name,int age){
              this.name=name;
              this.age=age;
       }
       public String toString(){
              return "姓名:"+this.name+" 年龄:"+this.age;
       }
       public boolean equals(Object obj){
              if(obj==this){
                     return true;
              }
              if(!(obj instanceof Person)){
                     return false;
              }
              Person p=(Person)obj;
              if(p.name.equals(this.name) && p.age==this.age){
                     return true;
              }
              return false;
       }
       public int hashCode(){
              return this.name.hashCode()*this.age;
       }
}
public class TestJava{
       public static void main(String args[]){
              Map<Person,String> map=new IdentityHashMap<Person,String>();
              map.put(new Person("霞",24),"kasumi");
              map.put(new Person("霞",24),"momiji");
              Set<Map.Entry<Person,String>> allSet=map.entrySet();
              Iterator<Map.Entry<Person,String>> iter=allSet.iterator();
              while(iter.hasNext()){
                     Map.Entry<Person,String> me=iter.next();
                     System.out.println(me.getKey()+" --> "+me.getValue());
              }
       }
}
D:\>javac TestJava.java
D:\>java TestJava
姓名:霞 年龄:24 --> momiji
姓名:霞 年龄:24 --> kasumi