HashMap initialization parameters (load / initialcapacity)

Question

What values should I pass to create an efficient HashMap / HashMap based structures for N items?

In an ArrayList, the efficien

Answer 1

The answer Yuval gave is only correct for Hashtable. HashMap uses power-of-two buckets, so for HashMap, Zarkonnen is actually correct. You can verify this from the source code:

  // Find a power of 2 >= initialCapacity
  int capacity = 1;
  while (capacity < initialCapacity)
  capacity <<= 1;

So, although the load factor of 0.75f is still the same between Hashtable and HashMap, you should use an initial capacity n*2 where n is the number of elements you plan on storing in the HashMap. This will ensure the fastest get/put speeds.