java 集合 HashMap 重写hashCode（） equals（）方法来存放自定义类对象

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map.Entry;
import java.util.Set;

public class HashMapTest 
{  
    public static void main(String[] args) 
    {  
        HashMap<IdNumber, String> hs2=new HashMap<IdNumber,String>();
        hs2.put(new IdNumber(2000), "小明");
        hs2.put(new IdNumber(2001), "小花");
        hs2.put(new IdNumber(2002), "小莉");
        System.out.println("hs2="+hs2);
        //key [2000]已经存在， key[2000] 的 value域由"王五"替换“小明”
        String farmerValue=hs2.put(new IdNumber(2000),"王五");
        System.out.println("farmerValue="+farmerValue);
        System.out.println("hs2="+hs2);
        //遍历输出：
        //生成封装了 key-value的Set集合
        Set<Entry<IdNumber, String>> entryhs2=hs2.entrySet();
        Iterator<Entry<IdNumber, String>> entryit=entryhs2.iterator();
        while(entryit.hasNext())
        {
        Entry<IdNumber, String> entryElement=entryit.next();
        IdNumber key=entryElement.getKey();
        String value=entryElement.getValue();
        System.out.println("key="+key+" value="+value);
        }


    }  
}  
class IdNumber
{
private int IdNumber;
public IdNumber() {
// TODO Auto-generated constructor stub
}
public IdNumber(int IdNumber)
{
this.IdNumber=IdNumber;
}
@Override
public String toString() {
// TODO Auto-generated method stub
return "["+this.IdNumber+"]";
}
@Override
public boolean equals(Object obj) 
{
if(obj==this)//自己和自己比较
return true;//那就是同一个相等了
//传入的引用不为空，而且两个的类型一样
if(obj!=null&&obj.getClass()==this.getClass())
{
IdNumber idNumber2=(IdNumber) obj;//类型转换
return this.IdNumber==idNumber2.IdNumber;
//如果两个的编号一样，那就认为相等
}
return false;
}
@Override
public int hashCode() {
// TODO Auto-generated method stub
return this.IdNumber*100;
}
}

//结果如下：