Here are couple of questions based on my interview experience, Please update/Comment. 1. Why string is immutable in java ? 2. What is Serializable and Externalizable in java ? How to customize serialization process ? 3. Can we serialize static variables of class ? 4. Static variables are associated with class or Object ? 5. At which level serialization happens object or class ? 6. Can transient variable be serialized explain ? 7. how to make any class immutable in java ? 8. Difference between String Builder and String Buffer ?? 9. How to revers any string example String test=new String("I am ashish") output should be "ashish am i" ? 10. write down sql query for finding out name of employee and there manager . Employee Table with 3 column E_Name E_Name Manager_ID Where Manager_ID is the subset of E_ID 11. what is instance variable, static variable in java ? Adding few more questions - 1. why hashtable allow null key and values not hashmap 2. what is t