*
 * @author Louis Wasserman
 * @since 12.0
 */
@GwtIncompatible
public abstract class ForwardingNavigableMap<K extends @Nullable Object, V extends @Nullable Object>
    extends ForwardingSortedMap<K, V> implements NavigableMap<K, V> {

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

  @Override
  protected abstract NavigableMap<K, V> delegate();

  @Override

 *
 * @author Louis Wasserman
 * @since 12.0
 */
@GwtIncompatible
public abstract class ForwardingNavigableMap<K extends @Nullable Object, V extends @Nullable Object>
    extends ForwardingSortedMap<K, V> implements NavigableMap<K, V> {

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

  @Override
  protected abstract NavigableMap<K, V> delegate();

  @Override

    @Override
    protected SortedSet<String> delegate() {
      return delegate;
    }
  }

  private static class NonNavigableSortedMap extends ForwardingSortedMap<String, String> {

    private final SortedMap<String, String> delegate = new SafeTreeMap<>(Ordering.natural());

    @Override
    protected SortedMap<String, String> delegate() {
      return delegate;

    @Override
    protected SortedSet<String> delegate() {
      return delegate;
    }
  }

  private static class NonNavigableSortedMap extends ForwardingSortedMap<String, String> {

    private final SortedMap<String, String> delegate = new SafeTreeMap<>(Ordering.natural());

    @Override
    protected SortedMap<String, String> delegate() {
      return delegate;