Java Streams


Hello there, fellow coder! Ever found yourself tangled in a web of complex loops and conditional statements? Well, Java Streams are here to save the day! They’re a modern feature that can make your code cleaner and easier to understand. Let’s dive in, shall we?

What are Java Streams?

Java Streams are a nifty feature introduced in Java 8. They’re all about making your life easier when dealing with sequences of data. But don’t confuse them with I/O streams; these are two different beasts. Java Streams are designed to efficiently process data, especially in bulk.

Creating Java Streams

Creating a stream in Java is a piece of cake. You can create them from collections, arrays, values, or even functions. Let’s see how it’s done.

From Collections and Arrays

List<String> myList = Arrays.asList("apple", "banana", "cherry");
Stream<String> myStream =;

In this example, we’re creating a stream from a list of strings.

From Values

Stream<String> myStream = Stream.of("apple", "banana", "cherry");

Here, we’re creating a stream directly from values.

From Functions

Stream<Integer> myStream = Stream.iterate(0, n -> n + 2).limit(10);

In this case, we’re creating a stream from a function. This will generate a stream of the first ten even numbers.

Understanding Stream Operations

Java Streams have two types of operations: intermediate and terminal. Intermediate operations are operations that transform a stream into another stream, like filter and map. Terminal operations produce a result or a side-effect, like collect and forEach.

Intermediate Operations


myStream.filter(s -> s.startsWith("a")).forEach(System.out::println);

This code filters the stream to only include strings that start with “a”, and then prints each one.


This code transforms each string in the stream to uppercase, and then prints each one.

Terminal Operations


List<String> myList = myStream.collect(Collectors.toList());

This code collects all the elements of the stream into a list.



This code performs an action for each element of the stream, in this case, printing each one.

Java Stream Characteristics

Java Streams can be sequential or parallel, and they can even be infinite!

Sequential vs Parallel Streams

Sequential streams process elements one after the other, while parallel streams can process elements simultaneously, making use of multiple threads.

Infinite Streams

Infinite streams don’t have a fixed size, and they can potentially process an infinite amount of data.

Advanced Stream Concepts

Ready to take your Java Stream skills to the next level? Let’s talk about collectors and stream pipelines.


Collectors are a powerful tool that allow you to accumulate elements of a stream into a single result.

Stream Pipeline

A stream pipeline is a sequence of stream operations, which can be as simple or as complex as you need it to be.

Java Streams Examples

Now, let’s put everything together with some complete code examples.

Code Example 1

List<String> fruits = Arrays.asList("apple", "banana", "cherry", "date", "elderberry");
    .filter(f -> f.length() > 5)

In this example, we’re creating a stream from a list of fruits. We then filter the stream to only include fruits with more than 5 letters, transform them to uppercase, sort them, and then print each one. The output will be:


Code Example 2

List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
int sum =
    .filter(n -> n % 2 == 0)
System.out.println("The sum of even numbers is " + sum);

In this example, we’re creating a stream from a list of numbers. We then filter the stream to only include even numbers, convert them to integers, sum them up, and then print the sum. The output will be:

The sum of even numbers is 30


And there you have it! You’ve just taken a deep dive into the world of Java Streams. They’re a powerful tool in your Java toolkit, and mastering them can help you write cleaner, more efficient code.

Frequently Asked Questions (FAQ)

Here are some popular questions related to Java Streams.

  1. How to understand Java streams?

    Java streams are a feature in Java 8 that allow you to process collections of data in a functional programming style. They are designed to make it easier to perform complex data processing tasks, such as filtering, mapping, and reducing data.

  2. What are Java streams explained simply?

    Java streams are like assembly lines in a factory. You have a source of data, which is processed step by step through a pipeline. Each step can transform the data in some way, like filtering out unwanted elements or converting elements to a different form.

  3. What are Java streams useful for?

    Java streams are useful for processing collections of data. They can be used to filter, transform, and aggregate data in a declarative and often more readable way than using loops and conditional statements.

  4. What are the basic types of Java streams?

    There are two basic types of Java streams: sequential and parallel. Sequential streams process data in the order it appears in the source, while parallel streams can process data simultaneously, potentially making use of multiple cores of your CPU.

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Happy coding!

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