FluentIterator implements ImmutableIterator<T> { @SuppressWarnings("unchecked") public FluentIterator<T> filter(Predicate<? super T> p) { return fluent(Iterators.filter(this, p)); } FluentIterator(Iterator<T> t); static FluentIterator<T> fluent(Iterator<T> t); @Override boolean hasNext(); @Override T next(); boolean weakEquals(Iterator<T> s, int n); @SuppressWarnings("unchecked") FluentIterator<T> filter(Predicate<? super T> p); boolean any(Predicate<? super T> p); boolean all(Predicate<? super T> p); @SuppressWarnings("unchecked") FluentIterator<T> concat(Iterator... ts); FluentIterator<T> peek(Consumer<? super T> cs); List<T> take(int n); List<T> takeAll(); FluentIterator<T> limit(int n); List<FluentIterator<T>> tee(int n); FluentIterator<Pair<T, S>> zip(Iterator<S> s, boolean weak); FluentIterator<List<T>> groupBy(Function<T, K> key); FluentIterator<List<T>> groupBy(); FluentIterator<T> skipDuplicates(Function<T, K> key); FluentIterator<T> skipDuplicates(); FluentIterator<T> keepFirst(Function<? super T, ? extends K> key); FluentIterator<T> keepLast(Function<? super T, ? extends K> key); FluentIterator<V> map(Function<T, V> f); FluentIterator<T> map(Iterator<T> t, BinaryOperator<T> f); T reduce(BinaryOperator<T> f); V reduce(BiFunction<V, T, V> f, V start);  }
@Test public void testFilter() { FluentIterator<Integer> t = fluent(unaryGenerator(1, x -> x + 1)).limit(10); BinaryOperator<Integer> acc = (a, b) -> a + b; int sum = reduce(t.filter(x -> x % 2 == 0), acc); assertEquals(30, sum); }