Re: Updating an object in a HashMap

import java.util.HashMap;
import java.lang.System;;

public class HashMapTest
{
    public static void main(String args[])
    {
        HashMap<String,Integer> hm = new HashMap<String,Integer>();

        hm.put("test1",0);

        hm.get("test1").intValue() += 5;
        //Error:The left-hand side of an assignment must be a variable

        System.out.println(hm.get("test1"));
    }

}

I want to update a Value in a HashMap. I know the Key. I would have
assumed the above code would work. Instead, I am given an error, "The
left-hand side of an assignment must be a variable".

Does this mean that the value returned is the literal value? In this
case 0. I would have assume a reference to the object would have been
returned and calling += would have unboxed the Integer and aggregated
the value.

Could someone explain to me what is going on? Also, what is the best
way to accomplish updating this value?