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Lesson 10 - Introduction to StreamAPI and lambda expressions in Java

In the previous lesson, The Collections Java utility class - Creating collections, we learned about the Collections library class and its utility methods. In today's Java tutorial, we're going to focus on StreamAPI, a set of tools for querying data. It's a very useful technology that makes collections easier to work with and saves many lines of code compared to regular use of loops.


StreamAPI is a new abstract layer to process data in collections. Along with StreamAPI, which came with Java version 8, lambda expressions simplifying queries considerably have also appeared. This approach to collections can remind you of SQL.

Every stream goes through the following three stages:

Stream cycle
  • creation - we create streams from data or generate them by generators
  • modification - each stream modification creates a new stream
  • consumption - we use the stream result, store data to a collection

Motivational example

Let's have a small example before we go on. Create a new project, it's going to be a console application named StreamAPI. We'll create a simple String collection:

List<String> jmena = Arrays.aslist("David", "Martin", "Dan", "Peter", "Michael", "Elisabeth");

Now, we select and print the items from this array that are longer than 5 characters, using a StreamAPI query. We'll write the following code into the program, which we're going to explain right after:


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Article description

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In this tutorial, we'll introduce StreamAPI technology and the basics of querying data in Java. We'll explain how StreamAPI works and learn simple queries.

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Article has been written for you by Petr Štechmüller