*
 * @author Dimitris Andreou
 */
@Immutable
@ElementTypesAreNonnullByDefault
abstract class AbstractCompositeHashFunction extends AbstractHashFunction {

  @SuppressWarnings("Immutable") // array not modified after creation
  final HashFunction[] functions;

  AbstractCompositeHashFunction(HashFunction... functions) {
    for (HashFunction function : functions) {
      checkNotNull(function);
    }

 *
 * @author Dimitris Andreou
 */
@Immutable
@ElementTypesAreNonnullByDefault
abstract class AbstractCompositeHashFunction extends AbstractHashFunction {

  @SuppressWarnings("Immutable") // array not modified after creation
  final HashFunction[] functions;

  AbstractCompositeHashFunction(HashFunction... functions) {
    for (HashFunction function : functions) {
      checkNotNull(function);
    }

    return new ConcatenatedHashFunction(list.toArray(new HashFunction[0]));
  }

  private static final class ConcatenatedHashFunction extends AbstractCompositeHashFunction {

    private ConcatenatedHashFunction(HashFunction... functions) {
      super(functions);
      for (HashFunction function : functions) {
        checkArgument(
            function.bits() % 8 == 0,

    return new ConcatenatedHashFunction(list.toArray(new HashFunction[0]));
  }

  private static final class ConcatenatedHashFunction extends AbstractCompositeHashFunction {

    private ConcatenatedHashFunction(HashFunction... functions) {
      super(functions);
      for (HashFunction function : functions) {
        checkArgument(
            function.bits() % 8 == 0,