How do you create a sequential stream from a collection?

Table of Contents

• Introduction
• Creating a Sequential Stream from a Collection
  • Using the stream() Method
    • Example:
  • Understanding Sequential vs Parallel Streams
    • Example with Sequential and Parallel Streams:
  • Using Streams with Other Collection Types
    • Example with a Set:
• Practical Examples of Sequential Streams
  • Example 1: Filtering and Collecting Data
  • Example 2: Mapping Elements
• Conclusion

Introduction

In Java, streams are a powerful feature introduced in Java 8 that allow you to process sequences of elements from a collection in a functional style. A sequential stream processes elements in a sequence, one at a time, in the order they appear in the collection. Creating a sequential stream from a collection is simple and is commonly used for tasks like filtering, mapping, and reducing data. This guide will explain how to create a sequential stream from a collection and provide practical examples.

Creating a Sequential Stream from a Collection

Using the stream() Method

The most common way to create a sequential stream from a collection in Java is by using the stream() method. This method is available on all Java collections that implement the Collection interface (such as List, Set, etc.).

Example:

Output:

In the above example, the stream() method creates a sequential stream from the numbers list. The filter() operation is then applied to keep only even numbers, and forEach() is used to print each number in the stream.

Understanding Sequential vs Parallel Streams

Java streams can be either sequential or parallel. By default, the stream() method creates a sequential stream, meaning the elements are processed one by one in the order they appear in the collection. If you want to process the elements in parallel, you can use the parallelStream() method, but for sequential processing, stream() is the appropriate choice.

Example with Sequential and Parallel Streams:

In this example, both sequential and parallel streams are demonstrated. For simple operations like printing, the difference may not be noticeable, but for more computationally heavy tasks, parallel streams can provide performance benefits.

Using Streams with Other Collection Types

You can use the stream() method with any collection type in Java that implements the Collection interface. For example, you can create streams from a Set, Queue, or Map.

Example with a Set:

Output:

Even though sets do not maintain a specific order, the sequential stream processes each element one at a time, and the order of output may not match the order of insertion.

Practical Examples of Sequential Streams

Example 1: Filtering and Collecting Data

You can use sequential streams to filter data based on certain conditions and collect the results into a new collection.

Output:

Example 2: Mapping Elements

Another common operation on streams is mapping, which allows you to transform elements in the stream. Here's an example where we convert a list of strings to their uppercase form.

Output:

Conclusion

Creating a sequential stream from a collection in Java is straightforward using the stream() method. This method allows you to process elements in a sequence, applying operations such as filtering, mapping, and collecting. Sequential streams are ideal for tasks where the order of processing is important or when working with relatively simple operations. Understanding how to use streams effectively can help you write cleaner, more efficient code by leveraging functional programming techniques in Java.