Java Interview Questions

1. Run time and Compile time Polymorphism
2. Overload Main Method
3. Program Without Main Method
4. Override Static Method
5. Object Oriented Programming over Procedural Programming
6. Abstract Classes VS Interfaces
7. Clubbing Exceptions in Catch Block
8. Try with Resources, Suppressed Exception, and Retrieving Suppressed Exception
9. Possibility when Finally Block is Not Executed
10. Exception Handling with Method Overriding
11. Explain Struts framework
12. Difference between request.getParameter() and request.getAttribute()
13. Difference between REST and SOAP web service
14. Difference between jsp:include and jsp:forward
15. How to create a Servlet
16. Brief about Collections hierarchy
17. Difference between different collection classes
18. Working of HashMap
19. Difference between Git Rebase and Git Reset
20. Brief about @Qualifier annotation in Spring
21. Explain different REST methods
22. Difference between Spring and SpringBoot
23. Explain Spring framework workflow
24. Explain SpringBoot framework workflow
25. Brief about contract between equals() and hashCode()
26. Useful methods in Java classes like Character, Arrays, String, Collections, Object
27. Difference between Comparator and Comparable
28. Difference between sleep, yield and wait methods
29. Can we create volatile array
30. Explain Cyclic Barrier in Multithreading
31. Difference between Association, Composition and Aggregation
32. What are different Application Context classes in Spring
33. Which classes are available in Spring for Handshake
34. Difference between Procedure and Function in PLSQL
35. Can we implement an interface without using implements
36. Brief about JSP and Servlet lifecycle
37. Explain CSRF, XSS, Brute Force, Denial of Service and CORS
38. Deep Copy vs Shallow Copy
39. Brief about Exception handling and Runtime, and Compile time exception (Read here)
    
40. Difference between webserver and appserver.

OOPs Concepts

Although its actually OOP concepts, but the most widely used term is OOPs Concepts. Though OOP stands for Object Oriented Programming, but what what does "s" stands for? System. "s" in OOPs stands for Object Oriented Programming System.

Lets talk about OOP concepts, the basics of all Programming Languages available today.

• Abstraction
• Encapsulation
• Polymorphism
• Inheritence

Abstraction

Abstraction is the concept of hiding the internal processing from outside world. We can implement abstraction using encapsulation and inheritance.

Encapsulation

Encapsulation is a means to achieve Abstraction. it is used to restrict the scope and usage of class members and methods. Access modifiers such as public, private and protected are used to restrict access.

Polymorphism

Polymorphism is a concept in which an object can behave differently based on different situations.
Polymorphism can further be classified into 2 categories, i.e. Run time Polymorphism, and Compile time polymorphism.

Inheritance
Inheritance is a means to achieve code reusability. It allows the properties of another class to be used in another class in a Parent-Child model. The class using the properties of another class is called the Derived class and the class whose properties are used by another class are called Base Class or Parent Class. Inheritance in Java is achieved using keyword "extends".
Types of Inheritance(in Java): Single Inheritance, Multilevel Inheritance, and Hybrid Inheritance