public final static Mutator getInstance(int mutatorType) {
		Mutator mutator = mutators.get(mutatorType);
		if (mutator != null)
			return mutator;
		switch (mutatorType) {
		case MUTATOR_IDENTITY:
			mutator = new IdentityMutator();
			break;
		case MUTATOR_SUBSTITUTION:
			mutator = new SubstitutionMutator();
			break;
		case MUTATOR_DELETION:
			mutator = new DeletionMutator();
			break;
		case MUTATOR_INSERTION:
			mutator = new InsertionMutator();
			break;
		case MUTATOR_MIXED:
			mutator = new MixedMutator();
			break;
		}
		if (mutator != null)
			mutators.put(mutatorType, mutator);
		return mutator;
	}