code: @Override
      public boolean add(E e) {
          if (e == null)
              throw new NullPointerException("e == null");
          elements[tail] = e;
          if ((tail = (tail + 1) & (elements.length - 1)) == head)
              doubleCapacity();
          return true;
      }
docs: Inserts the specified element at the end of this queue.
  
  <p>This method is equivalent to {@link #offer}.
  
  @param e the element to add
  @return <tt>true</tt> (as specified by {@link Collection#add})
  @throws NullPointerException if the specified element is null