Solving Your TreeSet Integration Troubles: Create a Custom Collection with Absolute Sorting

Описание: Learn how to resolve issues with your custom `SortedByAbsoluteValueIntegerSet` collection in Java and understand the importance of proper inheritance in collections.
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This video is based on the question https://stackoverflow.com/q/68966519/ asked by the user 'Tom' ( https://stackoverflow.com/u/16190453/ ) and on the answer https://stackoverflow.com/a/68966786/ provided by the user 'Louis Wasserman' ( https://stackoverflow.com/u/869736/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Solving Your TreeSet Integration Troubles: Create a Custom Collection with Absolute Sorting

If you've ever worked with Java's collection framework, you know how powerful and flexible it can be. However, creating your own custom collection can lead to some tricky issues, especially when trying to combine functionality from different classes. This post addresses a common problem encountered when creating a custom collection, specifically when extending TreeSet and attempting to override its functionality.

In this scenario, a developer tried to implement a collection that sorts Integer elements based on their absolute values. While the initial implementation seemed promising, it presented a challenge with the toString() method, which didn't operate as expected. Let's explore this problem and the solution in detail.

The Problem

The developer created a class named SortedByAbsoluteValueIntegerSet that extends TreeSet but also contains an instance of TreeSet as a field:

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

This implementation attempts to manage its own TreeSet (mySet) to provide specific behavior, however, it leads to confusion.

The critical issue arises from the fact that two separate TreeSet instances exist within this class:

The parent TreeSet (SortedByAbsoluteValueIntegerSet) that you are extending.

The mySet field that you created.

Consequence of Dual TreeSet Usage

This dual usage means that when elements are added to mySet, they aren't recognized by the toString() method of the parent class, which relies on the inherited TreeSet instance. The result is that your tests cannot see the elements, and the output is not aligning with expectations.

The Solution: Changing Your Approach

Step 1: Eliminate Redundancies

One key recommendation is to not extend TreeSet if you are also maintaining a separate instance of TreeSet within your class. Instead, choose one method of implementation. In this case, you should opt for extending AbstractSet or implementing Set, which allows you to define custom behavior without conflicting with built-in methods.

Step 2: Implementing the Custom Set

Below is a revised approach that utilizes AbstractSet for custom collection management:

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

Step 3: Verifying the Implementation

Now, your toString() implementation will correctly reflect the contents of the mySet because you have eliminated the confusion of two separate instances. Additionally, your size method and iterator will also function reliably.

Conclusion

Creating custom collections in Java can be rewarding but tricky. By carefully managing inheritance and composition, you can avoid common pitfalls—such as those seen with TreeSet management. Remember that adhering to a single-source of truth for the underlying data structure enhances clarity and predictability.

Feel free to experiment with the provided example and tailor it further to meet your needs. Happy coding!