What are the differences between HashSet and TreeSet in Java?

What are the differences between HashSet and TreeSet in Java?

HashSet and TreeSet are both implementations of the Set interface in Java, but they have key differences. HashSet is backed by a hash table and offers constant time performance for basic operations like add, remove, and contains. However, it does not maintain any order of elements. On the other hand, TreeSet is backed by a red-black tree and maintains a sorted order of its elements, which means operations like add and remove take O(log n) time.

When should I use HashSet over TreeSet?

You should use HashSet when you need fast access and don't care about the order of elements. It's ideal for scenarios where performance is critical and you just need to ensure uniqueness. Use TreeSet when you need to maintain a sorted order of elements or need to perform range queries.

Are there any performance trade-offs I should be aware of?

Yes, the main trade-off is performance versus order. HashSet offers faster performance for basic operations, while TreeSet has slower performance due to the overhead of maintaining order. If you frequently need to access elements in a sorted manner, the performance cost of TreeSet may be justified.

Can you give an example of when to use each?

Sure! Use HashSet for storing unique user IDs where order doesn't matter. Use TreeSet for storing a list of names that you want to display in alphabetical order.