hashmap-Java中遇到的一個異常Exception in thread main java.lang.NullPointerException

Java中遇到的一個異常Exception in thread "main" java.lang.NullPointerException

import java.util.*;

public class NewHashTest
{
public static void main(String[] args)
{
HashMap hash = new HashMap();
Emp emp1 = new Emp("laoda","111",123f);
Emp emp2 = new Emp("laoer","222",234f);
Emp emp3 = new Emp("laosan","333",5466f);

    hash.put(111,emp1);
    hash.put(222,emp2);
    hash.put(333,emp3);

    if(hash.containsKey(111))
    {
        Emp em = (Emp)hash.get(111);
        em.info();//可以正常顯示
    }

    Iterator iter = hash.keySet().iterator();

    while(iter.hasNext())
    {
        String key = iter.next().toString();
        Emp ems = (Emp)hash.get(key);
        ems.info();//這裡會報錯
    }
}

}

class Emp
{
String name;
String number;
float slary;

public void info()
{
    System.out.println("名字叫："+name);
    System.out.println("編號為："+number);
    System.out.println("薪水是："+slary);
}

public Emp(String name,String number,float slary)
{
    this.name = name;
    this.number = number;
    this.slary = slary;
}

}

會在ems.info();一行報一個Exception in thread "main" java.lang.NullPointerException的錯誤，是不是傳入的KEY類型有問題，還是什麼別的問題，求指點。

最佳回答：

map設置的鍵值對的時候鍵 hash.put(111,emp1) 111為int類型，而遍歷的時候確
String key = iter.next().toString();
使用String類型作為查找的key，當然就會是null了。

可將111 222 改成字符