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Discover best practices for efficiently mapping and filtering collections in Java using Streams. Learn how to write clean, maintainable code.
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This video is based on the question https://stackoverflow.com/q/62994336/ asked by the user 'Alain Duguine' ( https://stackoverflow.com/u/11917995/ ) and on the answer https://stackoverflow.com/a/62994634/ provided by the user 'Michael' ( https://stackoverflow.com/u/1898563/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Mastering Java Streams: A Guide to Mapping and Filtering Collections

Java Streams — a powerful feature introduced in Java 8 — can help simplify your code when working with collections. Stream operations are a great way to enhance readability and maintainability of your code while ensuring you're harnessing power and efficiency. However, understanding the best practices behind mapping and filtering can sometimes be a challenge, especially for beginners. In this post, we’ll explore how to effectively map and filter a collection of objects in Java using Streams, based on a practical example.

The Problem at Hand

Let’s consider a common scenario where you need to find restaurants within a specific geographic area based on latitude, longitude, and radius. You have a List<Restaurant> containing multiple entities, and you want to calculate the distance from a specific location for each restaurant, filtering and sorting them accordingly.

Here’s a snippet presented in a user’s question:

[[See Video to Reveal this Text or Code Snippet]]

While this works, there are several ways it can be improved. Let's break it down and refactor it for better clarity and performance using the ideal Java Streams practices.

Breaking Down the Solution

Streamlining the Process

The original approach involves modifying the restaurant objects directly through setDistance, which can lead to side effects and reduce code clarity. Instead, we can adopt a more functional approach that avoids mutating the state of our objects. Here’s how we can do it:

Use Filter and Map Separately: First, we want to filter out restaurants without latitude information.

Map the Remaining Entities: After filtering, we'll map each restaurant to a new object that holds both the restaurant and its calculated distance.

Proceed to Filter Again: Filter the mapped objects based on the distance criteria.

Sorting and Pagination: Finally, sort, skip and limit the results as needed.

Refactored Code Example

Here’s how the improved code looks with these considerations:

[[See Video to Reveal this Text or Code Snippet]]

Why Use a Pair Class?

In the refactored code, we've introduced the concept of a Pair class to store both the restaurant and its computed distance without modifying the original restaurant object. This helps keep our code clear and avoids introducing unnecessary state changes — a common code smell in functional programming contexts.

Benefits of this Approach

Clarity: By separating concerns, your functions carry clear responsibilities.

Maintainability: Reducing side effects makes future changes easier to handle.

Performance: This method can be more efficient, as it minimizes unnecessary computations.

Conclusion

In summary, utilizing Java Streams for mapping and filtering collections can help you produce cleaner and more efficient code. By avoiding side effects and embracing a functional approach, you can achieve better results in less time, paving the way for scalable applications. Next time you're faced with manipulating collections in Java, remember to leverage the full power of Streams!

Implement these best practices and take your Java programming skills to the next level.