Java 8 Stream (java.util.stream)

Java 8 Stream (java.util.stream)

Stream :

A stream is not a data structure; it takes input from underlying Collections, Arrays or any other objects. Stream work on underlying object and don’t change the original object. There are various intermediate operations on stream which returns a stream again. There is also terminal operation which terminates the process and collect the result.

In a nut shell stream is wrapper around underlying data which has multiple operation to allow process the bulk data operation easily.

Create stream;

    1.   We can create stream using collection.

          Stream strm =  listObject.stream();

    2.    Using array Object

           Stream strm = Stream.of(array);

    3.    Using any String or Integer value.

           Stream<Integer> strm =  Stream.of(1,3,4,6,4);

    4.    We can create empty stream

            Stream<String> emptyStream = Stream.empty();

    5.    Using Stream builder

            Stream builder= Stream.builder();

            Stream<String> strm =   builder.add("A").build();

Intermediate operations

Java 8 stream has intermediate operations which return itself a stream. Intermediate operations don't get executed until terminal operations called. All Intermediate operations are lazy.

1.    Stream filter( Predicate predicate)

      

        example:

        Stream strm = Stream.of(1,4,6,2,3);

        Stream strm2 = strm.filter(value -> value >4)

        long counter = strm2.count();

2.    map function :

        It returns a stream consisting of the results of replacing each element of the given stream with the         contents of a mapped stream.

        Suppose we have stream of Integer and we we want to convert each integer value multiply by 2.

        We can achieve this using map().

        

        List<Integer> list = Arrays.asList(5,3,6,7);   

        list.stream().map(num -> num * 2).forEach(System.out::println);




3.  flatmap :

        

        flatmap() is a combination of map & flat operation,  it applies function on element and flatterns             them.

        { {1,2}, {3,4}, {5,6} } -> flatMap -> {1,2,3,4,5,6}

Terminal operation

1.    collect :

        Return the result of intermediate operation.

        List<String> strm = Arrays.asList("one","two","three","four");

        List<String> data = strm.stream().filter(s -> s.startsWith("o")).collect(Collectors.toList());

2.    forEach :

        Iterate through the elements in the stream

        List<String> strm = Arrays.asList("one","two","three","four");

        strm.stream().filter(s -> s.startsWith("o")).forEach(s -> System.out.println(s));

3.    reduce :