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Java 8 - Streams - Actions - Collect

  • collect operation on stream is used to retrieve the result of a stream operation

int stream one to three
IntStream oneToThree = IntStream.of(1, 2, 3);


converting stream transformation result to set
Set resultSet = oneToThree.boxed().filter(number -> number > 2).collect(Collectors.toSet()); 

converting stream transformation result to list
List resultList = oneToThree.boxed().filter(number -> number > 2).collect(Collectors.toList());


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Java 8 - Streams - Introduction

Streams provide extended functionality to collections. All collection operations except operations on Map can be extended using streams.Streams can either be sequential or parallel.Operations on sequential streams are performed on a single thread.Operations on parallel streams are performed concurrently on multiple threads, and so are faster than sequential streams (although item order is affected). NOTE that parallel streams are CPU intensive and should be used with care as it can lead to starvation of other processes in your application.Operations on streams are grouped into intermediate (transformations) and terminal (actions).Stream processing is triggered only by terminal operations, while intermediate operations return a new stream.
an empty stream
Stream emptyStream = Stream.empty();

creating a stream from array
Stream<Integer> streamFromArray = Stream.of(new Integer[]{1,2,3});
Stream<Integer> streamFromArray2 = Integer[]{1,2,3});

creating a stream…

Java 8 - Streams - Parallel Stream

Operations on parallel streams are performed concurrently on multiple threads and so are faster than sequential streams (although item order is affected)However, operations on parallel streams can be ordered using 'stream.forEachOrdered'
parallel Integer Stream
Stream<Integer> parallelIntegerStream = new ArrayList<>(Arrays.asList(1,2,3)).parallelStream();

another parallel Integer Stream
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parallel String Stream
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Java 8 - Streams - Actions - Reduce

reduce operation on stream provides a way to accumulate the result of an operation which traverses all items in the stream.The traversal starts from the leftmost item in the stream.There are three implementations of the reduce operation.The first implementation uses the first item in the stream as initial accumulator.The second implementation expects an initial accumulator input.The third implementation provides a way to return an accumulator which has a different type from the stream items. This is similar to foldLeft in other functional languages e.g. Scala.
int stream one to three IntStream oneToThree = IntStream.of(1, 2, 3);

int stream one to two
IntStream oneToTwo = IntStream.of(1, 2);

string stream
Stream stringStream = Stream.of("a", "ab", "abc", "abcd");

USAGE"first implementation - reducing oneToThree Integer stream by addition: " + oneToThree.reduce((acc, item) -> acc+item …