Finite Streams | Bounded Streams

March 14, 2020 admin

Ways of creating finite streams:

collection.stream() call on a Collection to get a stream of all the elements contained in that collection.

      List<Integer> list = List.of(2, 54, 567, 78, 23);
      Stream<Integer> streamIntegers = list.stream();

This gives a Stream of elements contained in the list. We can use this stream() method with every collection, but there is no direct way to create a stream from a map because the map has pairs of key-value unlike lists and other collections that have data arranged linearly.

There is no stream() method in Map. Though We have methods like entrySet() and keySet() and values() on a map, we can leverage them to create streams.

        Map<Integer,String> map = Map.of(1, "one", 2, "two", 3, "Three", 4, "four");
	
       //to get stream of entries	
	Stream<Entry<Integer,String>> entries = map.entrySet().stream();

       //to get stream of values
       Stream<String> values = map.values().stream();

       //to get stream of keys
       Stream<Integer> keys = map.keySet().stream();

Stream.of() call with the number of elements. This returns a sequential ordered stream whose elements are the specified values.

      Stream<String> streamStrings = Stream.of("Hey!", "Happy", "ThanksGiving");

We can create Streams holding any type of objects using Streams.of() method.

Arrays.stream(array) is used to create a stream of array elements. Unlike stream() method of Collection, Arrays.stream() is a static method, so we pass the array as argument.

      Integer[] arr1 = { 6, 7, 9, 23, 56 };
		Stream<Integer> str1 = Arrays.stream(arr1);

Note: If the array is primitive array then Arrays.stream() will return primitive stream.

Builder<T> builder() method of Stream returns a builder for the stream. Elements can get added to the builder by using add() method. Later to get the stream build() can be invoked, which returns Stream.

       Stream.Builder<String> builder = Stream.builder();

       builder.add("a");
       builder.add("b");

       //invoke build() when we need the stream
       Stream<String> stream = builder.build();

This approach of creating stream is more flexible than using the of() method, as we can add elements in stream whenever – wherever we want!

These were the approaches to create finite streams.

Java Streams

Finite Streams | Bounded Streams