Ninestars Information Technologies Research and Development Associate Interview Questions and Answers

Hashmap is a data structure that stores key-value pairs and allows for fast retrieval of values based on keys.

• Hashmap uses a hashing function to map keys to indices in an array.

• It allows for constant time complexity O(1) for insertion, deletion, and retrieval operations.

• Example: HashMap map = new HashMap<>(); map.put("key", 1); int value = map.get("key");

String is immutable, while StringBuffer is mutable in Java.

• String is immutable, meaning once created, it cannot be changed. StringBuffer is mutable and can be modified.

• StringBuffer is synchronized, making it thread-safe. String is not synchronized.

• StringBuffer is more efficient for concatenating multiple strings due to its mutable nature.

• Example: String str = "Hello"; StringBuffer sb = new StringBuffer("Hello");