public void addFirst(E e){
  if (e == null)   throw new NullPointerException("e == null");
  elements[head=(head - 1) & (elements.length - 1)]=e;
  if (head == tail)   doubleCapacity();
}

public void addFirst ( E e ) { if ( e == null ) throw new NullPointerException ( "e == null" ) ; elements [ head = ( head - 1 ) & ( elements . length - 1 ) ] = e ; if ( head == tail ) doubleCapacity ( ) ; }
inserts the specified element at the front of this deque .
