code: @Override
  	public int indexOf(long elem) {
  		for (int i = 0; i < size; i++)
  			if (elem==elementData[i])
  				return i;
  		return -1;
  	}
docs: Searches for the first occurrence of the given argument, testing
  for equality using the <tt>equals</tt> method.
  
  @param   elem   an object.
  @return  the index of the first occurrence of the argument in this
  list; returns <tt>-1</tt> if the object is not found.
  @see     Object#equals(Object)