What are the differences between List, Set, and Map in Java?

What are the differences between List, Set, and Map in Java?

In Java, List, Set, and Map are all part of the Collections Framework, but they serve different purposes. A List allows duplicate elements and maintains the order of insertion. A Set, on the other hand, does not allow duplicates and does not guarantee any specific order. A Map stores key-value pairs, where each key is unique, and it allows for efficient retrieval of values based on their keys.

Can you give examples of each?

Sure! For a List, you can use ArrayList or LinkedList. For a Set, HashSet and TreeSet are common implementations. For a Map, you can use HashMap or TreeMap. Here's a quick example:

• List: List<String> myList = new ArrayList<>();
• Set: Set<Integer> mySet = new HashSet<>();
• Map: Map<String, Integer> myMap = new HashMap<>();

When should I use a Set instead of a List?

You should use a Set when you want to ensure that there are no duplicate elements in your collection. If the order of elements is not important and you need fast lookups, a Set is a better choice. Use a List when you need to maintain the order of elements or allow duplicates.

What about performance differences?

Performance can vary based on the implementation. Generally, accessing elements in a List is O(1) for ArrayList, while adding or removing elements can be O(n) in the worst case. For a HashSet, adding, removing, and checking for existence are O(1) on average. However, TreeSet operations are O(log n) due to the underlying tree structure. Maps have similar performance characteristics to Sets for key operations.