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Functional Programming with Java Streams API

What You Will Learn

How to use Java Streams API to simplify code and make it more efficient
The difference between imperative and declarative programming
How to apply filter, map, and reduce operations to streams

Key Concepts

Java Streams API is a way to process data in a declarative manner, focusing on what needs to be done rather than how it’s done. It’s mainly used with collections, such as lists, sets, and maps. Streams have intermediate operators like filter, map, and reduce, which allow you to transform and process data. Terminal operators like collect, count, and forEach are used to finalize the stream operation and get the result. Understanding the difference between imperative and declarative programming is crucial for effectively using Java Streams API.

Code Examples

people.stream()
       .filter(p -> p.getAge() <= 18)
       .limit(10)
       .collect(toList());

This code snippet demonstrates how to filter people under 18, limit the result to 10, and collect the result into a list.

cars.stream()
    .filter(car -> car.getPrice() < 20000)
    .collect(toList());

This code filters cars with a price less than 20,000 and collects the result into a list.

Lesson Summary

In this lesson, we explored the basics of Java Streams API and how it can be used to simplify code and make it more efficient. We learned about the difference between imperative and declarative programming and how Java Streams API fits into the declarative programming paradigm. We also saw how to apply filter, map, and reduce operations to streams. The instructor provided examples of how to use Java Streams API to solve real-world problems, such as filtering data and transforming objects. By the end of this lesson, students should have a good understanding of how to use Java Streams API to process data in a declarative manner.

Practice Exercise

Open the “Getting Started” class and complete the method “findPeopleAgeLessOrEqual-to18”. Use Java Streams API to filter people under 18 and limit the result to 10. Then, modify the implementation to use a declarative approach with streams.

What Is Next

In the next lesson, we will dive deeper into the world of Java Streams API and explore more advanced topics, such as grouping, sorting, and joining streams. We will also learn how to handle errors and exceptions when working with streams.

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