public boolean contains( final Object  o ) {
    return o instanceof Integer && contains(((Integer) o).intValue());
  }
Test if {@code o} is in the set.  This is the uppercase {@link Integer}
version of contains, requires a type-check and auto-unboxing.  When
possible use the {@code int} version of {@link #contains(int)} for
efficiency.
@return <tt>true</tt> if i was in the set.
jctools-core/src/main/java/org/jctools/maps/NonBlockingSetInt.java