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Interview Questions and Answers for 'Apis' - 56 question(s) found - Order By Newest

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Very frequently asked. Among first few questions in almost all interviews. Among Top 5 frequently asked questions. Frequently asked in Indian service companies (HCL,TCS,Infosys,Capgemini etc based on multiple feedback ) and Epam Systems
  Q1. Difference between == and .equals() ?Core Java
Ans. "equals" is the method of object class which is supposed to be overridden to check object equality, whereas "==" operator evaluate to see if the object handlers on the left and right are pointing to the same object in memory.

x.equals(y) means the references x and y are holding objects that are equal. x==y means that the references x and y have same object.

Sample code:

String x = new String("str");
String y = new String("str");

System.out.println(x == y); // prints false
System.out.println(x.equals(y)); // prints true

  Sample Code for equals

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   Like         Discuss         Correct / Improve     java   string comparison   string   object class   ==    equals   object equality  operator   == vs equals   equals vs ==     Asked in 293 Companies      basic        frequent

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Frequently asked at Manhattan Associates ( Based on 2 feedback )
  Q2. What is a Lambda Expression ? What's its use ?Core Java
Ans. Its an anonymous method without any declaration.

Lambda Expression are useful to write shorthand Code and hence saves the effort of writing lengthy Code.

It promotes Developer productivity, Better Readable and Reliable code.

  Sample Code for lambda

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   Like         Discuss         Correct / Improve     java   java8   lambda expression   architecture     Asked in 58 Companies      expert        frequent

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  Q3. Explain OOPs

or

Explain OOPs Principles

or

Explain OOPs Concepts

or

Explain OOPs features

or

Tell me something about OOPs
Core Java
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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   Like         Discuss         Correct / Improve     oops  oops features     Asked in 260 Companies      basic        frequent


Frequently asked question in companies using Hibernate.
  Q4. What is Lazy Initialization in Hibernate ?Hibernate
Ans. It's a feature to lazily initialize dependencies , relationship and associations from the Database. Any related references marked as @OneToMany or @ManyToMany are loaded lazily i.e when they are accessed and not when the parent is loaded.

  Sample Code for Lazy Initialization

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   Like         Discuss         Correct / Improve     hibernate   lazy loading hibernate   lazy initialization hibernate   architecture     Asked in 77 Companies      Basic        frequent

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Very Frequently asked. Have been asked in HCL Technologies very frequently ( based on 3 feedback ). Among first few questions in many interviews.
  Q5. Differences between abstract class and interface ?Core Java
Ans. Abstract classes can have both abstract methods ( method declarations ) as well as concrete methods ( inherited to the derived classes ) whereas Interfaces can only have abstract methods ( method declarations ).

A class can extend single abstract class whereas it can implement multiple interfaces.

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   Like         Discuss         Correct / Improve     java   classes   abstract class   interfaces   abstract class vs interface   abstract classes vs interfaces     Asked in 82 Companies      basic        frequent


Very Frequently asked to fresh graduates and less experienced. Favorite question in Walk in drives. Frequently asked in Indian Services companies.
  Q6. Difference between Overloading and Overriding ?Core Java
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 companies using SOA.
  Q7. What are RESTful Web Services ?Rest
Ans. REST or Representational State Transfer is a flexible architecture style for creating web services that recommends the following guidelines -

1. http for client server communication,
2. XML / JSON as formatiing language ,
3. Simple URI as address for the services and,
4. stateless communication.

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   Like         Discuss         Correct / Improve     java   web services   rest   java   j2ee  architecture     Asked in 14 Companies      intermediate        frequent


Frequently asked to fresh graduates.
 Q8. What is ACID ?Database
Ans. ACID stands for Atomicity, Consistency, Isolation, Durability is a set of properties of database transactions.

Atomicity means all or nothing. i.e parts of a transaction shouldn't commit if any one of them fails. Either the whole transaction should succeed or it should be complete rollback.

Consistency means that any transaction should lead database from one stabe state to another.

Isolation means that the execution of transaction results in a system state that would be obtained if transactions were executed serially.

Durability means that when a transaction is committed it forms the permanent state of database.

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   Like         Discuss         Correct / Improve     database  acid     Asked in 7 Companies      Intermediate

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 Q9. Can we have multiple main methods in a single class ?Core Java
Ans. We can overload the main method by specifying different argument types. For example -

2 main methods with different arguments is perfectly legal

public static void main();
public static void main(String[] args);

The following are not legal as compiler will complain of duplicate methods

public static void main(String[] args);
public static void main(String[] args);

Even The following are not legal as we cannot overload on return types

public static String main(String[] args);
public static void main(String[] args);

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   Like         Discuss         Correct / Improve     main method     Asked in 2 Companies


Frequently asked to fresh graduates.
  Q10. What is a Deadlock ?Operating System
Ans. When two threads are waiting each other and cant precede the program is said to be deadlock.

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   Like         Discuss         Correct / Improve     java   threads   multi threading   operating system   deadlock  concurrency     Asked in 23 Companies      basic        frequent


  Q11. What is the use of Transient Keyword ?Core Java
Ans. It in Java is used to indicate that a field should not be serialized.

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   Like         Discuss         Correct / Improve     java   oops   serialization   transient   java keywords     Asked in 39 Companies      intermediate        frequent

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  Q12. What is reflection ?
Ans. It is the process of examining / modifying the behaviour of an object at runtime.

  Sample Code for reflection

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   Like         Discuss         Correct / Improve     java   reflection   reflection api   ebay   mindtree     Asked in 29 Companies      basic        frequent


Usually asked to entry level software developers.
  Q13. Write a program to swap two variables without using thirdCore Java
Ans. public static void main(String[] args) {
   int num1 = 1;   
   int num2 = 2;
   num1 = num1^num2;
   num2 = num1^num2;
   num1 = num1^num2;
   System.out.print("num1 = " + num1 +", num2 = "+num2);
}

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   Like         Discuss         Correct / Improve     code  coding     Asked in 37 Companies      basic        frequent


 Q14. What is an API ( Application Programming Interface ) ?
Ans. An API is a kind of technical contract which defines functionality that two parties must provide: a service provider (often called an implementation) and an application. an API simply defines services that a service provider (i.e., the implementation) makes available to applications.

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   Like         Discuss         Correct / Improve     j2ee   api   java      basic        frequent


Very frequently asked. Usually asked with questions related to String. Frequently asked at CTS / Cognizant
  Q15. What is an Immutable Object ?Core Java
Ans. Object that can't be changed after instantiation.

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   Like         Discuss         Correct / Improve     java   oops   immutable  immutability     Asked in 27 Companies      basic        frequent

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 Q16. What is JAXP ?Xml
Ans. Stands for Java API for XML Processing. This provides a common interface for creating and using SAX, DOM, and XSLT APIs in Java regardless of which vendor’s implementation is actually being used.

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 Q17. What is JAXB ?Xml
Ans. Stands for Java API for XML Binding. This standard defines a mechanism for writing out Java objects as XML and for creating Java objects from XML structures.

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   Like         Discuss         Correct / Improve     java   xml   markup language   java api for xml binding   jaxb   abbreviation   technologies     Asked in 2 Companies


  Q18. Write a method to check if input String is Palindrome?Core Java
Ans. private static boolean isPalindrome(String str) {

if (str == null)
return false;

StringBuilder strBuilder = new StringBuilder(str);

strBuilder.reverse();

return strBuilder.toString().equals(str);

}

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   Like         Discuss         Correct / Improve     java   string   stringbuilder   stringbuilder   string class   code   palindrome     Asked in 38 Companies      Basic        frequent


 Q19. How can we test methods individually which are not visible or declared private ?
Ans. We can either increase their visibility and mark them with annotation @VisibleForTesting or can use reflection to individually test those methods.

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   Like         Discuss         Correct / Improve     junit   reflection api   @visiblefortesting   white box tester


Recently asked in Capital One.
 Q20. What will happen if we call perform(null) ?

public void perform(Object obj) {
System.out.println("Object");
}

public void perform(Integer int) {
System.out.println("Integer");
}
Core Java
Ans. compiler will throws error as ambiguous methods

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   Like         Discuss         Correct / Improve     overloading   method overloading     Asked in 1 Companies      intermediate


 Q21. Can you explain the integration between API Gateway and Lambda if we wish to develop services using these tools.Amazon Web Services (AWS)
Ans. We can create API gateway and give the name of lambda function in order to be linked with lambda function, deploy the API and whenever request will be made from API it will directly be linked to lambda function to perform further process.

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   Like         Discuss         Correct / Improve     aws api gateway  aws lambda  aws serverless computing  amazon cloud serverless computing  amazon lambda


 Q22. What is marshalling ?Xml
Ans. Its the process of creating XML structures out of Java Objects which is used to traverse information across the network.

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   Like         Discuss         Correct / Improve     xml   java api for xml   marshalling   parser   sax   dom   technologies     Asked in 1 Companies


 Q23. What is unmarshalling ?
Ans. Its the process of creating Java Objects out of XML structures.

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   Like         Discuss         Correct / Improve     xml   java api for xml   unmarshalling   parser   sax   dom   architecture     Asked in 1 Companies


 Q24. Difference between PATH and CLASSPATH ?Operating System
Ans. PATH is the variable that holds the directories for the OS to look for executables. CLASSPATH is the variable that holds the directories for JVM to look for .class files ( Byte Code ).

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   Like         Discuss         Correct / Improve     java   path   classpath   byte code   jvm   basic interview question     Asked in 3 Companies      intermediate        rare


Very Frequently asked. Favorite question in walkins and telephonic interviews. Usually among first few questions. Asked in different variants. Must know for intermediate and expert professionals.Among Top 10 frequently asked questions.
  Q25. What is rule regarding overriding equals and hashCode method ?Core Java
Ans. A Class must override the hashCode method if its overriding the equals method.

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   Like         Discuss         Correct / Improve     java   collections   hashcode  hash code   equals   collections     Asked in 44 Companies      intermediate        frequent

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 Q26. Is It Good to use Reflection in an application ? Why ?Core Java
Ans. no, It's like challenging the design of application.

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   Like         Discuss         Correct / Improve     java   reflection api   yes-no   architecture     Asked in 1 Companies      intermediate


 Q27. Why is Reflection slower ?
Ans. Because it has to inspect the metadata in the bytecode instead of just using precompiled addresses and constants.

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   Like         Discuss         Correct / Improve     java   reflection   reflection api   architecture


 Q28. Can we extend an Enum ?Core Java
Ans. No. Enums are final by design.

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   Like         Discuss         Correct / Improve     java   enums   inheritance  object oriented programming (oops)  oops concepts   yes-no     Asked in 1 Companies      intermediate


 Q29. What is classpath in a project?Core Java
Ans. ClassPath is the path where Java looks for class files to resolve the dependencies. For example - If you are using a class "xyz" in your code and have specified the respective import, Where should Java look for the definition of xyz. Java determines using the class path settings.

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   Like         Discuss         Correct / Improve     java   classpath   classpath settings     Asked in 2 Companies


 Q30. What is RI or Reference Implementation ?
Ans. RI or Reference Implementation is a sample implementation provided for the API's / Specs, usually by their developers. This is usually a part of API documentation.

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   Like         Discuss         Correct / Improve     reference implementation   help docs   helpdocs   api    apis    api specs   documentation        rare


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