Java interview questions for Hadoop developer Part 2

Q11. Which of the following object oriented principal is met with method overloading in java
- Inheritance
- Polymorphism
- Inheritance 
Polymorphism

Q12. Which of the following object oriented principal is met with method overriding in java
- Inheritance
- Polymorphism
- Inheritance 
Polymorphism

Q13. What is the name of collection interface used to maintain unique elements 
Map

Q14. What access level do you need to specify in the class declaration to ensure that only classes from the same directory can access it? What keyword is used to define this specifier? It has to have default specifier.
You do not need to specify any access level, and Java will use a default package access level

Q15. What's the difference between a queue and a stack? 
Stacks works by last-in-first-out rule (LIFO), while queues use the FIFO rule

Q16. How can you write user defined exceptions in Java 
Make your class extend Exception Class

Q17. What is the difference between checked and Unchecked Exceptions in Java ? Give an example of each type 
All predefined exceptions in Java are either a checked exception or an unchecked exception. Checked exceptions must be caught using try .. catch() block or we should throw the exception using throws clause. If you dont, compilation of program will fail.
- Example checked Exception: ParseTextException
- Example unchecked exception: ArrayIndexOutOfBounds

Q18. We know that FileNotFoundExceptionis inherited from IOExceptionthen does it matter in what order catch statements for FileNotFoundExceptionand IOExceptipon are written? 
Yes, it does. The FileNoFoundExceptionis inherited from the IOException. Exception's subclasses have to be caught first.

Q19. How do we find if two string are same or not in Java. If answer is equals() then why do we have to use equals, why cant we compare string like integers 
We use method equals() to compare the values of the Strings. We can't use == like we do for primitive types like int because == checks if two variables point at the same instance of a String object.

Q20. What is "package" keyword 
This is a way to organize files when a project consists of multiple modules. It also helps resolve naming conflicts when different packages have classes with the same names. Packages access level also allows you to protect data from being used by the non-authorized classes