code: @Override
  	public int indexOf(Object elem) {
  		if (elem == null) return -1;
  		if (elem instanceof Number) return indexOf(((Number)elem).longValue());
  		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)