Why is the initialCapacity of Hashtable 11 while the DEFAULT_INITIAL_CAPACITY in HashMap is 16 and requires a power of 2?

Question

Comparing the HashMap and Hashtable source code in JDK 1.6, I saw the below code inside HashMap:

/**
 * The default initial capacity -          


        

Answer 1

This could help:

http://www.concentric.net/~Ttwang/tech/primehash.htm

Basicly, if I remember correctly, when you have a hash table with a size that is power of 2, it's easy to get a hash function based on the less relevant bits of the key.

Using a prime number (as in 11) as the size of the table, makes collision on the table rows less likely, so inserting is "cheaper".