Package org.apache.commons.lang3.stream

Class Streams.FailableStream<T>

java.lang.Object
org.apache.commons.lang3.stream.Streams.FailableStream<T>
Type Parameters:
T - The streams element type.
Enclosing class:
Streams
public static class Streams.FailableStream<T> extends Object
A reduced, and simplified version of a Stream with failable method signatures.

  • Constructor Details

    • FailableStream

      public FailableStream(Stream<T> stream)
      Constructs a new instance with the given stream.
      Parameters:
      stream - The stream.

  • Method Details

    • allMatch

      public boolean allMatch(FailablePredicate<T,?> predicate)
      Returns whether all elements of this stream match the provided predicate. May not evaluate the predicate on all elements if not necessary for determining the result. If the stream is empty then true is returned and the predicate is not evaluated.

      This is a short-circuiting terminal operation.

      Note This method evaluates the universal quantification of the predicate over the elements of the stream (for all x P(x)). If the stream is empty, the quantification is said to be vacuously satisfied and is always true (regardless of P(x)).
      Parameters:
      predicate - A non-interfering, stateless predicate to apply to elements of this stream
      Returns:
      true If either all elements of the stream match the provided predicate or the stream is empty, otherwise false.

    • anyMatch

      public boolean anyMatch(FailablePredicate<T,?> predicate)
      Returns whether any elements of this stream match the provided predicate. May not evaluate the predicate on all elements if not necessary for determining the result. If the stream is empty then false is returned and the predicate is not evaluated.

      This is a short-circuiting terminal operation.

      Note This method evaluates the existential quantification of the predicate over the elements of the stream (for some x P(x)).
      Parameters:
      predicate - A non-interfering, stateless predicate to apply to elements of this stream
      Returns:
      true if any elements of the stream match the provided predicate, otherwise false

    • assertNotTerminated

      protected void assertNotTerminated()
      Throws IllegalStateException if this stream is already terminated.
      Throws:
      IllegalStateException - if this stream is already terminated.

    • collect

      public <A, R> R collect(Collector<? super T,A,R> collector)
      Performs a mutable reduction operation on the elements of this stream using a Collector. A Collector encapsulates the functions used as arguments to collect(Supplier, BiConsumer, BiConsumer), allowing for reuse of collection strategies and composition of collect operations such as multiple-level grouping or partitioning.

      If the underlying stream is parallel, and the Collector is concurrent, and either the stream is unordered or the collector is unordered, then a concurrent reduction will be performed (see Collector for details on concurrent reduction.)

      This is a terminal operation.

      When executed in parallel, multiple intermediate results may be instantiated, populated, and merged so as to maintain isolation of mutable data structures. Therefore, even when executed in parallel with non-thread-safe data structures (such as ArrayList), no additional synchronization is needed for a parallel reduction.

      Note The following will accumulate strings into an ArrayList: 
       
     List<String> asList = stringStream.collect(Collectors.toList());

      The following will classify Person objects by city: 

       
     Map<String, List<Person>> peopleByCity = personStream.collect(Collectors.groupingBy(Person::getCity));

      The following will classify Person objects by state and city, cascading two Collectors together: 

       
     Map<String, Map<String, List<Person>>> peopleByStateAndCity = personStream
         .collect(Collectors.groupingBy(Person::getState, Collectors.groupingBy(Person::getCity)));
      Type Parameters:
      R - the type of the result
      A - the intermediate accumulation type of the Collector
      Parameters:
      collector - the Collector describing the reduction
      Returns:
      the result of the reduction
      See Also:

    • collect

      public <A, R> R collect(Supplier<R> supplier, BiConsumer<R,? super T> accumulator, BiConsumer<R,R> combiner)
      Performs a mutable reduction operation on the elements of this FailableStream. A mutable reduction is one in which the reduced value is a mutable result container, such as an ArrayList, and elements are incorporated by updating the state of the result rather than by replacing the result. This produces a result equivalent to: 
       
     R result = supplier.get();
     for (T element : this stream)
         accumulator.accept(result, element);
     return result;

      Like reduce(Object, BinaryOperator), collect operations can be parallelized without requiring additional synchronization.

      This is a terminal operation.

      Note There are many existing classes in the JDK whose signatures are well-suited for use with method references as arguments to collect(). For example, the following will accumulate strings into an ArrayList: 

       
     List<String> asList = stringStream.collect(ArrayList::new, ArrayList::add, ArrayList::addAll);

      The following will take a stream of strings and concatenates them into a single string: 

       
     String concat = stringStream.collect(StringBuilder::new, StringBuilder::append, StringBuilder::append).toString();
      Type Parameters:
      R - type of the result
      A - Type of the accumulator.
      Parameters:
      supplier - a function that creates a new result container. For a parallel execution, this function may be called multiple times and must return a fresh value each time.
      accumulator - An associative, non-interfering, stateless function for incorporating an additional element into a result
      combiner - An associative, non-interfering, stateless function for combining two values, which must be compatible with the accumulator function
      Returns:
      The result of the reduction

    • filter

      public Streams.FailableStream<T> filter(FailablePredicate<T,?> predicate)
      Returns a FailableStream consisting of the elements of this stream that match the given FailablePredicate.

      This is an intermediate operation.

      Parameters:
      predicate - a non-interfering, stateless predicate to apply to each element to determine if it should be included.
      Returns:
      the new stream

    • forEach

      public void forEach(FailableConsumer<T,?> action)
      Performs an action for each element of this stream.

      This is a terminal operation.

      The behavior of this operation is explicitly nondeterministic. For parallel stream pipelines, this operation does not guarantee to respect the encounter order of the stream, as doing so would sacrifice the benefit of parallelism. For any given element, the action may be performed at whatever time and in whatever thread the library chooses. If the action accesses shared state, it is responsible for providing the required synchronization.

      Parameters:
      action - a non-interfering action to perform on the elements

    • makeTerminated

      protected void makeTerminated()
      Marks this stream as terminated.
      Throws:
      IllegalStateException - if this stream is already terminated.

    • map

      public <R> Streams.FailableStream<R> map(FailableFunction<T,R,?> mapper)
      Returns a stream consisting of the results of applying the given function to the elements of this stream.

      This is an intermediate operation.

      Type Parameters:
      R - The element type of the new stream
      Parameters:
      mapper - A non-interfering, stateless function to apply to each element
      Returns:
      the new stream

    • reduce

      public T reduce(T identity, BinaryOperator<T> accumulator)
      Performs a reduction on the elements of this stream, using the provided identity value and an associative accumulation function, and returns the reduced value. This is equivalent to: 
       
     T result = identity;
     for (T element : this stream)
         result = accumulator.apply(result, element)
     return result;
      but is not constrained to execute sequentially.

      The identity value must be an identity for the accumulator function. This means that for all t, accumulator.apply(identity, t) is equal to t. The accumulator function must be an associative function.

      This is a terminal operation.

      Note Sum, min, max, average, and string concatenation are all special cases of reduction. Summing a stream of numbers can be expressed as: 
       
     Integer sum = integers.reduce(0, (a, b) -> a + b);
      or: 
       
     Integer sum = integers.reduce(0, Integer::sum);

      While this may seem a more roundabout way to perform an aggregation compared to simply mutating a running total in a loop, reduction operations parallelize more gracefully, without needing additional synchronization and with greatly reduced risk of data races.

      Parameters:
      identity - the identity value for the accumulating function
      accumulator - an associative, non-interfering, stateless function for combining two values
      Returns:
      the result of the reduction

    • stream

      public Stream<T> stream()
      Converts the FailableStream into an equivalent stream.
      Returns:
      A stream, which will return the same elements, which this FailableStream would return.