DBS Bank Senior Software Developer interview questions

-Why is String immutable in Java? Difference between == and .equals()? Why must we override hashCode() when overriding equals()? What is the internal working of HashMap? What is load factor and default capacity of HashMap? Difference between HashMap and Hashtable? Difference between ArrayList and LinkedList? What is fail-fast and fail-safe iterator? What happens if two keys have the same hashCode? What is the difference between final, finally, and finalize? What is the difference between checked and unchecked exceptions? What is marker interface? What is serialization?