private final NavigableMap<K, V> delegate;

  public SafeTreeMap() {
    this(new TreeMap<K, V>());
  }

  public SafeTreeMap(Comparator<? super K> comparator) {
    this(new TreeMap<K, V>(comparator));
  }

  public SafeTreeMap(Map<? extends K, ? extends V> map) {
    this(new TreeMap<K, V>(map));
  }

  public SafeTreeMap(SortedMap<K, ? extends V> map) {
    this(new TreeMap<K, V>(map));
  }

  private final NavigableMap<K, V> delegate;

  public SafeTreeMap() {
    this(new TreeMap<K, V>());
  }

  public SafeTreeMap(Comparator<? super K> comparator) {
    this(new TreeMap<K, V>(comparator));
  }

  public SafeTreeMap(Map<? extends K, ? extends V> map) {
    this(new TreeMap<K, V>(map));
  }

  public SafeTreeMap(SortedMap<K, ? extends V> map) {
    this(new TreeMap<K, V>(map));
  }

  }

  @Override
  public boolean isEmpty() {
    return delegate.isEmpty();
  }

  @Override
  public Iterator<E> iterator() {
    return delegate.iterator();
  }

  @Override
  public E last() {
    return delegate.last();
  }

  @Override
  public @Nullable E lower(E e) {
    return delegate.lower(checkValid(e));
  }

  @Override
  public @Nullable E pollFirst() {

    // for testing SortedSet and SortedMap methods
    public static final String BEFORE_FIRST = "\0";
    public static final String BEFORE_FIRST_2 = "\0\0";
    public static final String MIN_ELEMENT = "a";
    public static final String AFTER_LAST = "z";
    public static final String AFTER_LAST_2 = "zz";
  }

  public static class Chars extends SampleElements<Character> {
    public Chars() {

    // for testing SortedSet and SortedMap methods
    public static final String BEFORE_FIRST = "\0";
    public static final String BEFORE_FIRST_2 = "\0\0";
    public static final String MIN_ELEMENT = "a";
    public static final String AFTER_LAST = "z";
    public static final String AFTER_LAST_2 = "zz";
  }

  public static class Chars extends SampleElements<Character> {
    public Chars() {

  }

  public void testOf() {
    assertEquals("training", Optional.of("training").get());
  }

  public void testOf_null() {
    try {
      Optional.of(null);
      fail();
    } catch (NullPointerException expected) {
    }
  }

  public void testFromNullable() {
    Optional<String> optionalName = Optional.fromNullable("bob");
    assertEquals("bob", optionalName.get());
  }

  public static final Integer zero = 0;
  public static final Integer one = 1;
  public static final Integer two = 2;
  public static final Integer three = 3;
  public static final Integer four = 4;
  public static final Integer five = 5;
  public static final Integer six = 6;
  public static final Integer seven = 7;
  public static final Integer eight = 8;
  public static final Integer nine = 9;

    @Override
    public boolean apply(@Nullable Integer i) {
      return (i.intValue() & 1) == 1;
    }

    @Override
    public int hashCode() {
      return 0x150dd;
    }

    @Override
    public boolean equals(@Nullable Object obj) {
      return obj instanceof IsOdd;
    }

    @Override
    public String toString() {
      return "IsOdd";
    }
  }

    }
  }

  public void testSize0() {
    Iterator<String> iterator = Iterators.emptyIterator();
    assertEquals(0, Iterators.size(iterator));
  }

  public void testSize1() {
    Iterator<Integer> iterator = Collections.singleton(0).iterator();
    assertEquals(1, Iterators.size(iterator));
  }

  public void testSize_partiallyConsumed() {

    public long getAccessTimestamp() {
      return accessTimestamp;
    }

    public long getWriteTimestamp() {
      return writeTimestamp;
    }

    public boolean equals(Object o) {
      return value.equals(o);
    }

    public int hashCode() {
      return value.hashCode();
    }
  }

  /**
   * LocalManualCache is a wrapper around LocalCache for a cache without loading.
   *