Interview Questions and Answers for 'Api' | Search Interview Question

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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 )

Q31. Why is String immutable in Java ?

Core 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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Q32. 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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Very Frequently asked to fresh graduates and less experienced. Favorite question in Walk in drives. Frequently asked in Indian Services companies.

Q33. 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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Q34. 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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Very frequently asked. Usually asked with questions related to String. Frequently asked at CTS / Cognizant

Q35. What is an Immutable Object ?

Core Java

Ans. Object that can't be changed after instantiation.

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Frequently asked to fresh graduates.

Q36. 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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Q37. 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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Q38. 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 vendorâ€™s implementation is actually being used.

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Q39. 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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Q40. 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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Q41. What is unmarshalling ?

Ans. Its the process of creating Java Objects out of XML structures.

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Q42. 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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Q43. 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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Very frequently asked in companies using SOA.

Q44. 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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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.

Q45. 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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Q46. 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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Q47. 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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Frequently asked question in companies using Hibernate.

Q48. 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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Frequently asked at Manhattan Associates ( Based on 2 feedback )

Q49. 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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Q50. 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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Q51. Can we extend an Enum ?

Core Java

Ans. No. Enums are final by design.

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Q52. 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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Very Frequently asked. Have been asked in HCL Technologies very frequently ( based on 3 feedback ). Among first few questions in many interviews.

Q53. 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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Q54. 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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Q55. Explain the challenging problems you faced recently and how you overcame it ?

General

Ans. [Open Ended Answer]

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Must know at all levels. Among Top 10 frequently asked questions in Java. Very frequently asked to fresh graduates or less experienced professionals.

Q56. What is Inheritance ?

Core Java

Ans. Its a facility for code reuse and independent extension wherein a derived class inherits the properties of parent class.

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Recently asked in Capital One.

Q57. 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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