Java Stream API in Detail

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Introduction

In Java programming, one of the most common tasks is to process data — filter it, transform it, or summarise it.

Before Java 8, this was typically done using verbose for loops and conditionals. While effective, this approach often led to so much boilerplate code and hard-to-maintain code.

Java 8 introduced the Stream API, a powerful tool for working with sequences of data in a more functional and declarative way. Streams make it easier to express data processing queries clearly and concisely.

In this article, We'll break down key concepts, cover how streams work under the hood, explain the different types of operations, and provide practical examples.

1. Traditional Approach Using for Loops

Let’s say you want to get even numbers from a list:

List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6);
List<Integer> evenNumbers = new ArrayList<>();

for (Integer number : numbers) {
    if (number % 2 == 0) {
        evenNumbers.add(number);
    }
}
System.out.println(evenNumbers); // Output: [2, 4, 6]