Re: Updating an object in a HashMap

From:
Knute Johnson <nospam@rabbitbrush.frazmtn.com>
Newsgroups:
comp.lang.java.programmer
Date:
Wed, 13 Feb 2008 16:03:12 -0800
Message-ID:
<47b38540$0$1599$b9f67a60@news.newsdemon.com>
alacrite@gmail.com wrote:

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;

// the equivalent of this line is
// 0 += 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?

Thanks.


int newValue = hm.get("test1") + 5;
hm.put("test1",newValue);

--

Knute Johnson
email s/nospam/knute/

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