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Ans. Abstraction is a process of hiding the implementation details and describing only the functionality to the user.

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Q4. Can you explain software design principles cohesion and coupling with an example?

^{This question was recently asked at 'Fidelity Information Services (FIS)'.This question is still unanswered. Can you please provide an answer.}

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Q5. Can you write the code for implementing the one to many (student -> courses) relationship in hibernate?

Hibernate

Ans. @OneToMany(cascade = CascadeType.ALL)
@JoinColumn(name = "student_id")
private Set countries;

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Q6. Explain OOPs

or

Explain OOPs Principles

or

Explain OOPs Concepts

or

Explain OOPs features

or

Tell me something about OOPs

Ans. OOPs or Object Oriented Programming is a Programming model which is organized around Objects instead of processes. Instead of a process calling series of processes, this model stresses on communication between objects. Objects that all self sustained, provide security by encapsulating it's members and providing abstracted interfaces over the functions it performs. OOP's facilitate the following features

1. Inheritance for Code Reuse
2. Abstraction for modularity, maintenance and agility
3. Encapsulation for security and protection
4. Polymorphism for flexibility and interfacing

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Q7. Is there any relationship between Web.xml and Spring.xml ?

Ans. No, there is no relationship between web.xml and spring.xml but you have to configure spring.xml in web.xml in order initialize beans when application starts up

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Q8. What is Spring Security ?

Ans. http://www.java4s.com/java-servlet-tutorials/difference-between-servletconfig-and-servletcontext-in-java/

Ans. Spring Security is a powerful and highly customizable authentication and access control framework. It is the de facto standard for securing Spring-based applications.

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Q9. What is the difference between ServletConfig and ServletContext ?

Java EE

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Very Frequently asked to Senior Software Engineers or Developers.

Q10. Describe some of the Design Patterns you have used ?

Ans. [Open Ended Answer]

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Q11. What are design situations to use Singleton and Prototype Design Pattern ?

Ans. Both are creational design patterns.

Singleton is used when we would like to reuse an object if object is not supposed to hold request or thread specific information. Inversely Prototype is used in situations where we would like to reuse the object information but the request / thread may require it own data to be persisted.

In short, Singleton is used in situations where we can live with single object being shared across multiple requests or threads whereas Prototype is used when we need duplicate copies of objects.

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Frequently asked in Infosys India

Q12. What is a String Pool ?

Ans. String pool (String intern pool) is a special storage area in Java heap. When a string is created and if the string already exists in the pool, the reference of the existing string will be returned, instead of creating a new object and returning its reference.

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Advanced level question. Frequently asked in High end product companies. Frequently asked in Google , Cognizant and Deloitte ( Based on 2 feedback )

Q13. Why is String immutable in Java ?

Ans. 1. String Pool - When a string is created and if it exists in the pool, the reference of the existing string will be returned instead of creating a new object. If string is not immutable, changing the string with one reference will lead to the wrong value for the other references.

Example -

String str1 = "String1";
String str2 = "String1"; // It doesn't create a new String and rather reuses the string literal from pool

// Now both str1 and str2 pointing to same string object in pool, changing str1 will change it for str2 too

2. To Cache its Hashcode - If string is not immutable, One can change its hashcode and hence it's not fit to be cached.

3. Security - String is widely used as parameter for many java classes, e.g. network connection, opening files, etc. Making it mutable might possess threats due to interception by the other code segment.

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Q14. What is HTTP ?

Java EE

Ans. HTTP or Hypertext Transfer Protocol is internet protocol for tranmission of hypertext ( text with meta data ) over internet.

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Very Frequently asked to fresh graduates and less experienced. Favorite question in Walk in drives. Frequently asked in Indian Services companies.

Q15. Difference between Overloading and Overriding ?

Ans. Overloading - Similar Signature but different definition , like function overloading.

Overriding - Overriding the Definition of base class in the derived class.

Sample Code for overloading

Sample Code for overriding

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Very frequently asked in different variations. Frequently asked in Deloitte ( 2 feedback ) , HCL Tech ( 3 feedback ), TCS and Coginizant (CTS)

Q16. Explain the scenerios to choose between String , StringBuilder and StringBuffer ?

or

What is the difference between String , StringBuilder and StringBuffer ?

Ans. If the Object value will not change, use String Class because a String object is immutable.

If the Object value can change and will only be modified from a single thread, use StringBuilder because StringBuilder is unsynchronized(means faster).

If the Object value may change, and can be modified by multiple threads, use a StringBuffer because StringBuffer is thread safe(synchronized).

Sample Code for String

Sample Code for StringBuffer

Sample Code for StringBuilder

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Recently asked in TCS , Tech Mahindra, HCL , Accenture and Fidelity.

Q17. Explain Flow of Spring MVC ?

Ans. The DispatcherServlet configured in web.xml file receives the request.

The DispatcherServlet finds the appropriate Controller with the help of HandlerMapping and then invokes associated Controller.

Then the Controller executes the logic business logic and then returns ModeAndView object to the DispatcherServlet.

The DispatcherServlet determines the view from the ModelAndView object.

Then the DispatcherServlet passes the model object to the View.

The View is rendered and the Dispatcher Servlet sends the output to the Servlet container.

Finally Servlet Container sends the result back to the user.

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Q18. What bean scopes does Spring support? Explain them.

Ans. The Spring Framework supports following five scopes -

Singleton
prototype
request
session
global-session

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Very frequently asked.Usually among first few questions.

Q19. What is MVC ?

Ans. MVC is a Design Pattern that facilititates loose coupling by segregating responsibilities in a Web application

1. Controller receives the requests and handles overall control of the request
2. Model holds majority of the Business logic, and
3. View comprise of the view objects and GUI component

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Very frequently asked in HCL Tech ( Based of 4 inputs )

Q20. Write a program to reverse a string iteratively and recursively ?

Ans. Using String method -

new StringBuffer(str).reverse().toString();

Iterative -

public static String getReverseString(String str){
StringBuffer strBuffer = new StringBuffer(str.length);
for(int counter=str.length -1 ; counter>=0;counter--){
strBuffer.append(str.charAt(counter));
}
return strBuffer;
}

Recursive -

public static String getReverseString(String str){
if(str.length <= 1){
return str;
}
return (getReverseString(str.subString(1)) + str.charAt(0);
}

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Q21. What are the different types of inheritance in Hibernate ?

Hibernate

Ans. Table Per Class , Table per Sub Class , Table per Concrete Class

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Very frequently asked Hibernate interview question. Frequently asked in TCS ( based on 2 feedback )

Q22. What are different types of associations in Hibernate ?

Hibernate

Ans. There are 4 types of associations in Hibernate

One to One
One to Many
Many to One
Many to Many

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Very frequently asked. Usually followed by questions related to private constructor and synchronized access. Frequently asked in JPMorgan and TCS (Based on 2 feedback)

Q23. Explain Singleton Design Pattern ?