return new Joiner(this) {
      @Override
      public <A extends Appendable> A appendTo(
          A appendable, Iterator<? extends @Nullable Object> parts) throws IOException {
        checkNotNull(appendable, "appendable");
        checkNotNull(parts, "parts");
        while (parts.hasNext()) {
          Object part = parts.next();
          if (part != null) {
            appendable.append(Joiner.this.toString(part));

          Function<? super T, ? extends K> keyFunction,
          Function<? super T, ? extends V> valueFunction,
          BinaryOperator<V> mergeFunction) {
    checkNotNull(comparator);
    checkNotNull(keyFunction);
    checkNotNull(valueFunction);
    checkNotNull(mergeFunction);
    return Collectors.collectingAndThen(
        Collectors.toMap(
            keyFunction, valueFunction, mergeFunction, () -> new TreeMap<K, V>(comparator)),

  public void testCheckNotNull_simple_success() {
    String result = Preconditions.checkNotNull(NON_NULL_STRING);
    assertSame(NON_NULL_STRING, result);
  }

  public void testCheckNotNull_simple_failure() {
    try {
      Preconditions.checkNotNull(null);
      fail("no exception thrown");
    } catch (NullPointerException expected) {
    }
  }

   * the behavior of this method is undefined but we make a reasonable effort at converting anyway.
   */
  public final String to(CaseFormat format, String str) {
    checkNotNull(format);
    checkNotNull(str);
    return (format == this) ? str : convert(format, str);
  }

  /** Enum values can override for performance reasons. */
  String convert(CaseFormat format, String s) {

   *
   * <p>The {@link InputStream} should not be read from before or after the hand-off.
   */
  public HashingInputStream(HashFunction hashFunction, InputStream in) {
    super(checkNotNull(in));
    this.hasher = checkNotNull(hashFunction.newHasher());
  }

  /**
   * Reads the next byte of data from the underlying input stream and updates the hasher with the
   * byte read.
   */
  @Override

    checkNotNull(cache);
    checkNotNull(key);
    LocalCache<K, V> map = toLocalCache(cache);
    return map.getEntry(key);
  }

  /**
   * Forces the segment containing the given {@code key} to expand (see {@link Segment#expand()}).
   */
  static <K, V> void forceExpandSegment(Cache<K, V> cache, K key) {
    checkNotNull(cache);
    checkNotNull(key);

  @CheckForNull @LazyInit F function;

  AbstractTransformFuture(ListenableFuture<? extends I> inputFuture, F function) {
    this.inputFuture = checkNotNull(inputFuture);
    this.function = checkNotNull(function);
  }

  @Override
  @SuppressWarnings("CatchingUnchecked") // sneaky checked exception
  public final void run() {
    ListenableFuture<? extends I> localInputFuture = inputFuture;

   */
  public static <T extends @Nullable Object> Iterable<T> filter(
      final Iterable<T> unfiltered, final Predicate<? super T> retainIfTrue) {
    checkNotNull(unfiltered);
    checkNotNull(retainIfTrue);
    return new FluentIterable<T>() {
      @Override
      public Iterator<T> iterator() {
        return Iterators.filter(unfiltered.iterator(), retainIfTrue);
      }
    };

   *     helpful predefined constants
   * @return the buffered reader
   */
  public static BufferedReader newReader(File file, Charset charset) throws FileNotFoundException {
    checkNotNull(file);
    checkNotNull(charset);
    return new BufferedReader(new InputStreamReader(new FileInputStream(file), charset));
  }

  /**
   * Returns a buffered writer that writes to a file using the given character set.
   *

  MapIteratorCache(Map<K, V> backingMap) {
    this.backingMap = checkNotNull(backingMap);
  }

  @CanIgnoreReturnValue
  @CheckForNull
  final V put(K key, V value) {
    checkNotNull(key);
    checkNotNull(value);
    clearCache();
    return backingMap.put(key, value);
  }

  @CanIgnoreReturnValue
  @CheckForNull
  final V remove(Object key) {
    checkNotNull(key);
    clearCache();
    return backingMap.remove(key);