Скачать или смотреть How to Filter Java Streams with All Entries from Another List

Discover how to filter a list of arrays in Java streams to match `all` criteria from another list effectively.
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Filtering Java Streams: Finding All Matches from Another List

In Java programming, particularly when working with streams, you might encounter scenarios where you need to filter a list based on specific criteria. One such common problem arises when you're tasked with filtering contents of a list to ensure they contain all the entries from another list. This guide will address this problem and guide you through a clear solution using Java streams.

The Problem at Hand

Imagine you have a list of collections of numbers, like this one:

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Now you want to filter this list to find only those entries that match all the numbers in another criteria list, for instance:

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From the original list, the expected filtered results would be:

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This means you want to ensure each of the arrays in your initial list contains both numbers 1 and 2. Your initial attempt using the contains method might return results based on an "or" condition, which is not what you desire.

The Solution: Using Java Streams

To solve this problem of filtering based on "all" entries from another list, you can utilize the Java Streams API effectively. Here’s how to do it step by step:

Step 1: Define Your ProductData Class

Start by ensuring you have a class for your data. Suppose you're working with a class ProdData that contains a method to retrieve its chemical volumes:

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Step 2: Prepare Your Data

Next, create your list of ProdData objects as follows:

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And your criteria for filtering that you've defined as:

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Step 3: Implement the Stream Filter

Using the Java Streams API, you will filter the list of ProdData by ensuring that the chemVolumes in each ProdData entry contains all elements in matchingVolumes. Here’s the core line of the code to achieve that filtering:

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

Key Takeaway

This line of code leverages the filter method of the Stream API and the containsAll method of the Collection interface to ensure that only those entries from products are included in filteredProducts where all criteria are matched. This approach respects the requirement that the order of entries does not impact the matching process.

Conclusion

In conclusion, filtering lists in Java to match all entries of another list can be efficiently achieved using the Stream API. By defining appropriate methods in your data classes and applying the right filters, you can easily manage complex data queries while keeping your code clean and maintainable.

Feel free to adjust the example to fit your actual data structures and requirements, ensuring you follow the principles shared here. Happy coding!