Both HashSet and LinkedHashSet are useful data structures in Java, but they differ in their key characteristics:
Get Bikash Sahani’s stories in your inbox
Join Medium for free to get updates from this writer.
Order:
HashSet: Does not maintain any order of elements. The order can be unpredictable and even change over time. Use this when order doesn’t matter.
LinkedHashSet: Maintains the insertion order of elements. Elements are iterated over in the same order they were added. Use this when preserving order is important.
Underlying Data Structure:
HashSet: Uses a hash table for storage, providing fast addition, removal, and search (constant time complexity: O(1)).
LinkedHashSet: Combines a hash table and a doubly-linked list. The hash table ensures uniqueness, while the linked list remembers the insertion order. This adds some overhead compared to HashSet.
Performance:
HashSet: Generally faster than LinkedHashSet due to its simpler structure.
LinkedHashSet: Slightly slower than HashSet, but the performance difference is usually negligible for most use cases.
Memory Usage:
HashSet: Requires less memory as it only uses the hash table.
LinkedHashSet: Requires more memory due to the additional linked list.
Use Cases:
HashSet: Use when you need to store unique elements efficiently and order doesn’t matter (e.g., checking for duplicate items).
LinkedHashSet: Use when you need to preserve the insertion order of unique elements (e.g., maintaining the order of items added to a shopping cart).
Additional Notes:
Both HashSet and LinkedHashSet allow only one null value.
LinkedHashSet inherits from HashSet, so it also has all the functionalities of HashSet.
I hope this explanation clarifies the differences between HashSet and LinkedHashSet.
Feel free to ask if you have any further questions!
