Package org.apache.druid.java.util.common.guava

Interface Sequence<T>

All Known Implementing Classes:
BaseSequence, CombiningSequence, ConcatSequence, ExplodingSequence, FilteredSequence, FrameChannelSequence, LazySequence, MappedSequence, MergeSequence, OperatorSequence, ParallelMergeCombiningSequence, ScanQueryOffsetSequence, SimpleSequence, SkippingSequence, TopNSequence, YieldingSequenceBase
public interface Sequence<T>
A Sequence represents an iterable sequence of elements. Unlike normal Iterators however, it doesn't expose a way for you to extract values from it, instead you provide it with a worker (an Accumulator) and that defines what happens with the data.

This inversion of control is in place to allow the Sequence to do resource management. It can enforce that close() methods get called and other resources get cleaned up whenever processing is complete. Without this inversion it is very easy to unintentionally leak resources when iterating over something that is backed by a resource.

Sequences also expose {#see org.apache.druid.java.util.common.guava.Yielder} Yielder objects which allow you to implement a continuation over the Sequence. Yielder do not offer the same guarantees of automatic resource management as the accumulate method, but they are Closeable and will do the proper cleanup when close() is called on them.

  • Method Details

    • accumulate

      <OutType> OutType accumulate(OutType initValue, Accumulator<OutType,T> accumulator)
      Accumulate this sequence using the given accumulator.
      Type Parameters:
      OutType - the type of accumulated value.
      Parameters:
      initValue - the initial value to pass along to start the accumulation.
      accumulator - the accumulator which is responsible for accumulating input values.
      Returns:
      accumulated value.

    • toYielder

      <OutType> Yielder<OutType> toYielder(OutType initValue, YieldingAccumulator<OutType,T> accumulator)
      Return a Yielder for accumulated sequence.
      Type Parameters:
      OutType - the type of accumulated value.
      Parameters:
      initValue - the initial value to pass along to start the accumulation.
      accumulator - the accumulator which is responsible for accumulating input values.
      Returns:
      a Yielder for accumulated sequence.
      See Also:

    • map

      default <U> Sequence<U> map(Function<? super T,? extends U> mapper)

    • filter

      default Sequence<T> filter(com.google.common.base.Predicate<? super T> predicate)

    • toList

      default List<T> toList()
      This will materialize the entire sequence. Use at your own risk.

    • skip

      default Sequence<T> skip(long skip)

    • limit

      default Sequence<T> limit(long limit)

    • flatMap

      default <R> Sequence<R> flatMap(Function<? super T,? extends Sequence<? extends R>> mapper)

    • flatMerge

      default <R> Sequence<R> flatMerge(Function<? super T,? extends Sequence<? extends R>> mapper, com.google.common.collect.Ordering<? super R> ordering)

    • forEach

      default void forEach(Consumer<? super T> action)

    • withEffect

      default Sequence<T> withEffect(Runnable effect, Executor effectExecutor)

    • withBaggage

      default Sequence<T> withBaggage(Closeable baggage)