code: public boolean contains(Object o) {
          final ReentrantLock lock = this.lock;
          lock.lock();
          try {
              return indexOf(o) != -1;
          } finally {
              lock.unlock();
          }
      }
docs: Returns {@code true} if this queue contains the specified element.
  More formally, returns {@code true} if and only if this queue contains
  at least one element {@code e} such that {@code o.equals(e)}.
  
  @param o object to be checked for containment in this queue
  @return {@code true} if this queue contains the specified element