code: static Comparer<byte[]> getBestComparer() {
      try {
        Class<?> theClass = Class.forName(UNSAFE_COMPARER_NAME);
  
        // yes, UnsafeComparer does implement Comparer<byte[]>
        @SuppressWarnings("unchecked")
        Comparer<byte[]> comparer = (Comparer<byte[]>) theClass
            .getEnumConstants()[0];
        return comparer;
      } catch (Throwable t) { // ensure we really catch *everything*
        LOG.error("Loading lexicographicalComparerJavaImpl...");
        return lexicographicalComparerJavaImpl();
      }
    }
docs: Returns the Unsafe-using Comparer, or falls back to the pure-Java
  implementation if unable to do so.