Compare common collection choices using the operations your application performs most often.
The core idea
ArrayList is a good default for ordered data and indexed access. HashSet is useful for uniqueness and membership. HashMap supports key-based lookup. Linked structures can help in particular insertion/removal patterns but are not automatically faster for every operation.
A practical way to approach it
List the dominant operations before choosing a collection: append, indexed read, membership, key lookup, sorted traversal, or frequent removal. Consider iteration order and whether duplicate values are allowed. Use the collection interfaces in method signatures when possible.
Try it in a small project
Build a small benchmark with realistic data sizes to compare membership checks in a list and a set. Measure before optimizing and keep the benchmark separate from application tests.
Common mistakes to avoid
Big-O describes growth, not every constant cost. Memory overhead, cache behavior, data size, and access patterns can change the practical result.
Key takeaway
Keep the first version small, make your assumptions explicit, and verify the result with a repeatable test. For production use, check the current official documentation for the tools and versions you choose.