Thursday, January 22, 2009

HashMap and null keys

most of us know a hashMap allows null keys and also null values , but what if we add two values corresponding to same null key

      map.put(null,null);
     map.put(null,"D");
         map.put(null,"E");

What will be the output of
System.out.println(map)

will for the null key it will print the last key value pair , i.e. as per my understanding the null key is unique and on adding more value elements to the same null key will override the old values
at

3 comments:

  1. AnonymousMarch 19, 2009 at 5:05 AM

    it will return null in first case.
    'D' in second case.

    ReplyDelete
  2. AnonymousMarch 19, 2009 at 5:07 AM

    {null=E}

    ReplyDelete
  3. lazycoderMay 6, 2009 at 8:29 AM

    Bang on the target, the older values get overridden if new values are put into hashtable/hashMap using the same key.

    I posted a workaround for this a couple of days back, using an arrayList as a value is a better option, check out this example for adding multiple values to a key in hashmap :)

    http://lifeofalazycoder.blogspot.com/2009/05/java-adding-multiple-values-to-key-in.html

    ReplyDelete