Getting started with java-stream

Remarks#

This section provides an overview of what java-stream is, and why a developer might want to use it.

It should also mention any large subjects within java-stream, and link out to the related topics. Since the Documentation for java-stream is new, you may need to create initial versions of those related topics.

Installation or Setup

Detailed instructions on getting java-stream set up or installed.

Working with Java Stream Api (Java 8) in Android using Android Studio

Gradle Setup :

build.gradle(Module: app)

 compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }

     jackOptions {
            enabled true
        }

What is the Stream API ?

Stream is a new abstract layer introduced in Java 8. A stream is a sequence of elements (objects, primitive types) from the stream source. Therefore, stream is not a data structure and it doesn’t store the elements it works with. It can be of a finite or infinite size and allow effortless code parallelism

Advantage’s:

• It helps in using data in a declarative way. We can make use of Database functions like Max, Min etc., without running a full iteration.
• It makes good use of multi-core architectures without worrying about multi-threading code.
• We can create a pipeline of data operations with Java Stream that can run in a sequence or in parallel.
• It provides support for group by, order by etc. operations.
• It supports writing for code in Functional programming style.
• It provides parallel processing of data.

How streams work :

Normal Approach (Without using Stream Api) :

 List<Integer> numbers = new ArrayList<>();
    numbers.addAll(Arrays.asList(1, 20, 3, 10, 20, 30, 4, 50, 80, 1, 2));//adding dummy data

    int i = 0;
    List<String> number_str = new ArrayList<>();
    for (Integer num : numbers) {
        if (i >= 5)//after 5 loop will stop
            break;

        if (num >= 10) // check number greater than or equal to 10
        {
            number_str.add(String.format("Number %d", num));//Typecast Integer to String then add to String List
            i++;//increment i count
        }
    }

    number_str.sort(Comparator.naturalOrder());//sort the list

In Above code we created Integer List and add some data’s then Iterate using for loop. On each loop execution we check loop count(i >= 5) and num >=10. finally sort the string list.

Now, let’s rewrite the code using Java’s 8 Stream API:

  List<Integer> numbers = new ArrayList<>();
numbers.addAll(Arrays.asList(1, 20, 3, 10, 20, 30, 4, 50, 80, 1, 2));

List<String> number_str = numbers.stream()
        .filter(num -> num >= 10)//check num greater than 10
        .limit(5)//stop loop at 5
        .sorted()//sort the list
        .map(num -> String.format("Number %d", num))//typecast into String List
        .collect(Collectors.toList());