Basic of Java Streams – Beginner Tutorial

Introduction

Java streams are a powerful and popular feature in Java 8 and above that provide a functional approach to processing data collections. Streams make it easier to process large data sets by allowing developers to express complex data processing operations with a few lines of code. We will explore the basics of Java streams with code examples.

What are Java Streams?

In Java, a stream is a sequence of elements that supports various operations to perform computations on these elements. Streams can be created from a variety of data sources, for example, collections, arrays, and files.

The primary aim of streams is to provide a functional approach to processing data. Unlike traditional for-loops and while-loops, streams can be used to express complex data processing operations in a declarative style. In general, this makes code much more readable and concise and therefore easier to maintain.

Key Characteristics

• Streams are a sequence of elements that can be processed in parallel or in serial.
• Streams are not data structures; they do not store data, and they do not change the data source.
• Streams support various operations like filtering, mapping, and reducing data.
• Streams can be used to process both finite and infinite data sets.

How do streams work?

Java streams are based on the concept of pipelines. A pipeline is a sequence of operations that are applied to a stream. The result of one operation is the input to the next operation, and so on. The operations in a pipeline can be divided into two categories: intermediate and terminal.

Intermediate operations are used to transform the data in the stream. Examples of intermediate operations include filter, map, flatMap, and distinct. These operations do not modify the original data source but create a new stream as output.

Terminal operations are used to produce a result or a side effect. Examples of terminal operations include forEach, reduce, collect, and toArray. Only when a terminal operation is called, the pipeline will be executed, and the result is returned. After a terminal operation is called, the stream cannot be used again.

Examples

Let’s look at some code examples:

1. Example: List of Strings

In this example, we have a list of strings, and we want to filter the strings that contain the letters „e“

In this short code example, we have a list of Strings with different names, saved In variable names. Then we create a stream from the list by using the .streams() method. We apply the filter() intermediate operation to the stream, which filters out any strings that do not contain the letter ‚e‘. Finally, we use the collect() terminal operation to collect the filtered elements into a new list.

2. Mapping a list of integers

In this example, we have a list of integers, and we want to create a new list that contains the squares of these integers.

In this short code example, we first create a list of integers. We then create a stream from the list using the stream() method. We apply the map() intermediate operation to the stream, which maps each integer to its square. Finally, we use the collect() terminal operation to collect the squared integers into a new list.

Comparison to traditional loops – Streams vs Loops

In Java, traditional loops like for-loops and while-loops are used to iterate over collections and perform operations on each element. Traditional loops provide a procedural approach to processing data, where the developer specifies how to perform each operation on each element in the collection.

Traditional loops have some advantages, such as:

• Familiarity: Traditional loops are a well-known programming construct that many developers are already familiar with.
• Control: Traditional loops give developers precise control over the iteration process and the order in which operations are performed.
• Debugging: Traditional loops are easier to debug because the code is straightforward and easy to follow.

However, traditional loops have some disadvantages, such as:

• Boilerplate: Traditional loops require a lot of boilerplate code, such as initializing variables, checking conditions, and incrementing counters. This can make the code more verbose and harder to read.
• Readability: Traditional loops can be harder to read and understand, especially for complex operations that involve nested loops or conditional statements.
• Limited Parallelism: Traditional loops are not well-suited for parallel processing, which can limit their performance on large data sets.

Conclusion

In this article, we looked at the basic concepts of java streams.

We have seen that streams provide a functional approach to processing data, which makes it easier to write code that is more concise, more readable, and easier to maintain.

We have also looked at some code examples that illustrate how to use streams to filter, and map. These examples show that streams can be used to express complex data processing operations in a declarative style, which is more intuitive and easier to understand.

Java streams are a powerful and versatile feature of the Java programming language. By mastering the basics of Java streams, you can write code that is more efficient, more elegant, and more maintainable. Please take a look at the following content to know more about the different stream operations. Check out this article to get to know more about streams.