code: private void init(int initCapacity) {
          assert (initCapacity & -initCapacity) == initCapacity; // power of 2
          assert initCapacity >= MINIMUM_CAPACITY;
          assert initCapacity <= MAXIMUM_CAPACITY;
  
          threshold = (initCapacity * 3)/ 4;
          table = new long[2 * initCapacity];
      }
docs: Initializes object to be an empty map with the specified initial
  capacity, which is assumed to be a power of two between
  MINIMUM_CAPACITY and MAXIMUM_CAPACITY inclusive.