What are the performance differences between HashSet and ArrayList?

What are the performance differences between HashSet and ArrayList?

HashSet and ArrayList have different performance characteristics. HashSet offers O(1) time complexity for add, remove, and contains operations due to its underlying hash table structure. In contrast, ArrayList has O(n) time complexity for these operations because it relies on an array that may need to be resized or searched linearly.

When should I use HashSet instead of ArrayList?

You should use HashSet when you need fast lookups, uniqueness of elements, and don't care about the order of elements. Use ArrayList when you need to maintain the order of elements and allow duplicates.

Are there any memory usage differences between them?

Yes, HashSet generally uses more memory than ArrayList because it needs to store additional information for the hash table, such as hash codes and links between elements.

Can you give me an example of when to use each?

Sure! Use HashSet for a collection of unique user IDs where fast lookups are essential. Use ArrayList for a list of items in a shopping cart where the order matters and duplicates are allowed.