* @author Louis Wasserman
 * @since 2.0
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
public abstract class ForwardingSortedSet<E extends @Nullable Object> extends ForwardingSet<E>
    implements SortedSet<E> {

  /** Constructor for use by subclasses. */
  protected ForwardingSortedSet() {}

  @Override
  protected abstract SortedSet<E> delegate();

  @Override
  @CheckForNull

import junit.framework.TestSuite;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Tests for {@code ForwardingSortedSet}.
 *
 * @author Louis Wasserman
 */
public class ForwardingSortedSetTest extends TestCase {
  static class StandardImplForwardingSortedSet<T> extends ForwardingSortedSet<T> {
    private final SortedSet<T> backingSortedSet;

    StandardImplForwardingSortedSet(SortedSet<T> backingSortedSet) {

import junit.framework.TestSuite;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Tests for {@code ForwardingSortedSet}.
 *
 * @author Louis Wasserman
 */
public class ForwardingSortedSetTest extends TestCase {
  static class StandardImplForwardingSortedSet<T> extends ForwardingSortedSet<T> {
    private final SortedSet<T> backingSortedSet;

    StandardImplForwardingSortedSet(SortedSet<T> backingSortedSet) {

  @Override
  SortedSet<Integer> createUnfiltered(Iterable<Integer> contents) {
    final TreeSet<Integer> result = Sets.newTreeSet(contents);
    // we have to make the result not Navigable
    return new ForwardingSortedSet<Integer>() {
      @Override
      protected SortedSet<Integer> delegate() {
        return result;
      }
    };
  }

  @Override

 *
 * @author Louis Wasserman
 * @since 12.0
 */
@GwtIncompatible
@ElementTypesAreNonnullByDefault
public abstract class ForwardingNavigableSet<E extends @Nullable Object>
    extends ForwardingSortedSet<E> implements NavigableSet<E> {

  /** Constructor for use by subclasses. */
  protected ForwardingNavigableSet() {}

  @Override
  protected abstract NavigableSet<E> delegate();

  @Override

      return set;
    }
    return new UnmodifiableNavigableSet<>(set);
  }

  static final class UnmodifiableNavigableSet<E extends @Nullable Object>
      extends ForwardingSortedSet<E> implements NavigableSet<E>, Serializable {
    private final NavigableSet<E> delegate;
    private final SortedSet<E> unmodifiableDelegate;

    UnmodifiableNavigableSet(NavigableSet<E> delegate) {

        throw new UnsupportedOperationException();
      }
    };
  }

  private static <E extends @Nullable Object> SortedSet<E> removeOnlySortedSet(
      final SortedSet<E> set) {
    return new ForwardingSortedSet<E>() {
      @Override
      protected SortedSet<E> delegate() {
        return set;
      }

      @Override
      public boolean add(@ParametricNullness E element) {

        throw new UnsupportedOperationException();
      }
    };
  }

  private static <E extends @Nullable Object> SortedSet<E> removeOnlySortedSet(
      final SortedSet<E> set) {
    return new ForwardingSortedSet<E>() {
      @Override
      protected SortedSet<E> delegate() {
        return set;
      }

      @Override
      public boolean add(@ParametricNullness E element) {