@Override
	public int hashCode() {
		int hash = MurmurHash.initialize();
		for (T[] bucket : buckets) {
			if ( bucket==null ) continue;
			for (T o : bucket) {
				if ( o==null ) break;
				hash = MurmurHash.update(hash, comparator.hashCode(o));
			}
		}

		hash = MurmurHash.finish(hash, size());
		return hash;
	}
Add {@code o} to set if not there; return existing value if already
there. This method performs the same operation as {@link #add} aside from
the return value.
runtime/Java/src/org/antlr/v4/runtime/misc/Array2DHashSet.java