code: public void ensureCapacity(int minCapacity) {
  	if (table.length < minCapacity) {
  		int newCapacity = nextPrime(minCapacity);
  		rehash(newCapacity);
  	}
  }
docs: Ensures that the receiver can hold at least the specified number of associations without needing to allocate new internal memory.
  If necessary, allocates new internal memory and increases the capacity of the receiver.
  <p>
  This method never need be called; it is for performance tuning only.
  Calling this method before <tt>put()</tt>ing a large number of associations boosts performance,
  because the receiver will grow only once instead of potentially many times and hash collisions get less probable.
  
  @param   minCapacity   the desired minimum capacity.