Скачать или смотреть How to Filter a Stream with Multiple Criteria in Java 8

Discover how to efficiently filter a list of `Student` objects in Java 8 using hierarchical conditions. Learn how to clean up your code with method chaining and Enums!
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Filtering a Stream with Multiple Criteria in Java 8

In Java programming, filtering a collection based on certain criteria is a common requirement. If you have a list of students and you want to filter out a single student based on hierarchical conditions, you might encounter a problem with code that becomes unwieldy and convoluted. This guide explores how to simplify this filtering process using Java 8's Stream API and Enums.

The Problem Statement

Imagine you have an ArrayList of Student objects with varying attributes. Your goal is to filter this list to return just one student based on the following rules:

Select the first student from the COMP (Computers) module.

If no COMP students are found, select from the ECON (Economics) module.

If no ECON students are found, select from the AGRI (Agriculture) module.

Continue this process, potentially adding more modules, until a student is found or all options are exhausted.

The original implementation could quickly become messy and difficult to manage as more conditions are introduced. Let's look at how we can implement a clean, efficient solution.

The Solution

Using a Loop for Simple Filtering

One of the easiest ways to optimize this would be to use a simple loop. Here's how to implement the filterStudent method using this approach:

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This method checks each module in order and filters the student list accordingly, returning the first match it finds.

Avoiding Multiple Iterations

While the above solution is clean, it still iterates through the student list for each module, which isn’t optimal. A more efficient approach would involve using a Comparator to define a priority order. Here’s how you can achieve that:

Define an Ordering Map: You can map module names to their priorities using a Map.

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Create a ToIntFunction: This will determine the order of each student based on their module.

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Create a Comparator: Define how comparisons should be made.

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Stream and Find the Minimum: Now, you can easily find the best (highest priority) student.

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Conclusion

By applying the principles of clean code and leveraging Java 8's Stream API, you can efficiently filter a list of students based on hierarchical conditions. This method streamlines the code, making it more manageable as more conditions are added. Whether using a simple loop or a more structured approach with comparators, both methods enhance clarity and efficiency.

This is a perfect example of how Java's powerful features can simplify complex logic in your code! Happy coding!