stream api in java

Streams in Java 8 represents a sequence of elements. It supports sequential as well as parallel operations.

The most important thing to know about streams is that it is not a separate Data Structure. It doesn’t store data. It just converts the input data whether it is a List or anything else into a sequence of streams.

They work with Functional Interfaces and Lambda Expressions which makes them so attractive to use.

So how does a stream look like?

import java.util.*;
 
public class MyClass {
 
    public static void main(String[] args) {
        List<String> names = Arrays.asList("David", "John", "Nathan", "Kevin");
 
        names.stream()
                   .map((n) -> n.toUpperCase())
                   .forEach(System.out::println);
    }
}

So here :>

We had a list of names initially which can be considered as an Input.
Then we convert it into a stream.
Then we map and convert it into UpperCase.
Finally using the ForEach we loop over the elements and display the names using Sys Out.

Here we had an intermediate operation which was converted to stream and a terminal operation which was forEach.

We can create an empty stream as well. It is done so that we can return a stream with 0 elements instead of null.
Stream s = Stream.empty()

This is how we create an empty stream.

Also we can get a stream eve without using a collection. Like in the above example which is took to display names in UPPER CASE, i took a collection and converted that into a Stream. But we can directly get a Stream as well without using a collection.

We use the Stream.of method here.

Stream streamArray =Stream.of("X","Y","Z");

Parallel Streams:>

You can create Parallel Stream using .parallel() method on Stream object in Java. Parallel Stream is a feature in Java 8 in which multiple cores of the processor will be used. Benefit is efficient processing and execution of data.

public class MyClass {
 
    public static void main(String[] args) {
        int[] array= {1,2,3,4,5};
 
        System.out.println("Use of Parallel Stream");
        IntStream intParallelStream=Arrays.stream(array).parallel();
        intParallelStream.forEach((s)->
        {
            System.out.println(s+" "+Thread.currentThread().getName());
        }
        );
    }
}

So here those 5 elements are getting ran in 5 cores by 5 threads. So accordingly you can see the output.

Parallel streams are used when performance is critical. Else a single serial stream is sufficient.

Hope the article was clear. Thanks for reading.

Tag: stream api in java

Java 8: Streams API