Frequently asked Interview Questions and Answers

Interview Questions and Answers - Order By Newest

Very frequently asked in phone and walk in interviews.

Q71. What are Marker Interfaces ? Name few Java marker interfaces ?

Core Java

Ans. An interface without any method declaration is called as marker interface. there are 3 in-built interfaces in JVM i.e. serializable, clonable, remote

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Frequently asked to fresh graduates.

Q72. Difference between Process and Thread ?

Operating System

Ans. Process is a program in execution whereas thread is a separate path of execution in a program.

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Q73. Explain Autoboxing ?

Core Java

Ans. Autoboxing is the automatic conversion that the Java compiler makes between the primitive types and their corresponding object wrapper classes

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Very frequently asked. Usually difference between String,StringBuffer and StringBuilder is asked in different variations.

Q74. Difference between StringBuffer and StringBuilder ?

Core Java

Ans. StringBuffer is synchronized whereas StringBuilder is not.

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Q75. 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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Q76. When do you get ClassCastException?

or

What is ClassCastException ?

Ans. As we only downcast class in the hierarchy, The ClassCastException is thrown to indicate that code has attempted to cast an object to a subclass of which it is not an instance.

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Q77. Similarity and Difference between static block and static method ?

Core Java

Ans. Both belong to the class as a whole and not to the individual objects. Static methods are explicitly called for execution whereas Static block gets executed when the Class gets loaded by the JVM.

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Q78. Can we overload main method in Java ?

Core Java

Ans. Yes, but the overloaded main methods without single String[] argument doesn't get any special status by the JVM. They are just another methods that needs to be called explicitly.

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Very Frequently asked.

Q79. Explain throw, throws , try and catch in Java ?

Core Java

Ans. throw is used to re throw an exception.throws is used to declare that the method throws the respective exceptions.try block is used to identify if the respective block has thrown any exception.catch is used to catch the exception that has been thrown by the respective try block.

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Usually asked to experienced developers.

Q80. What is a cyclic dependency ?

Maven

Ans. A has dependency of B, B has dependency of C and C has dependency of A

With Maven 2 , came transitive dependency wherein in above scenario, C will acts as a dependency of A as if this dependency has been defined directly in A but the negative side is that if it leads to cyclic dependency , it creates problems.

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Q81. Difference between GET and POST Requests ?

Web Service

Ans. GET is supposed to get information from the server. Client sends the minimal information so that Server can respond with the response body on basis of request. For example - You want to get complete employment record for employee id 123

POST is supposed to send the information for submission. Payload or a Body is usually sent so that it can be persisted on the server. For example - Sending the complete information of an employee ( id, name , dept etc ) to the server for persisting it.

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Q82. What is coupling and Cohesion ?

Design

Ans. Coupling is the degree of interdependence between software modules, a measure of how closely connected two modules are or the strength of the relationships between modules.

Cohesion refers to the degree to which the elements of a module belong together. Cohesion measures the strength of relationship between pieces of functionality within a given module.

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Frequently asked Generic Question.

Q83. Why do you want to work for our company ?

General

Ans. [Open Ended Answer]

Usually answered stating your keen interest in the role offered and challenges and opportunities the role offers.

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Q84. Why java doesn't support multiple Inheritance ?

or

Explain Java Diamond Problem.

Core Java

Ans. class A {
void test() {
System.out.println("test() method");
}
}

class B {
void test() {
System.out.println("test() method");
}
}

Suppose if Java allows multiple inheritance like this,

class C extends A, B {
}

A and B test() methods are inheriting to C class.

So which test() method C class will take? As A & B class test() methods are different , So here we would Facing Ambiguity.

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Usually asked to entry level software developers.

Q85. Write a program to swap two variables without using third

Core 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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Q86. What is JSON ?

Json

Ans. JSON is "JavaScript Object Notation", primarily used for client-server or server-server communication. Its a much lighter and readable alternative to XML. JSON is language independent and is easily parse-able in all programming languages.

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Q87. 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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Q88. 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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Q89. Which access specifier can be used with Class ?

Core Java

Ans. For top level class we can only use "public" and "default". We can use private with inner class.

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Q90. Different ways of implementing Threads in Java ?

Core Java

Ans. Threads in Java can be implement either by Extending Thread class or implementing runnable interface.

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Q91. What is a Final Method ?

Core Java

Ans. A Method that cannot be overriden in the sub class.

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Very Frequently asked.Favorite question in Walk in drive for many Indian service companies.

Q92. What is a Final Class ?

Ans. A Class that cannot be sub classed.

Sample Code for final class

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

Q93. What is an Immutable Object ?

Core Java

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

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Q94. Can we override static methods ? Why ?

Core Java

Ans. No.

Static methods belong to the class and not the objects. They belong to the class and hence doesn't fit properly for the polymorphic behavior.

A static method is not associated with any instance of a class so the concept of overriding for runtime polymorphism using static methods is not applicable.

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Q95. Name few Java Exceptions ?

Core Java

Ans. IndexOutofBoundException ,
NoClassDefFoundException ,
OutOfMemoryException ,
IllegalArgumentException,
NullPointerException,
IllegalStateException

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Q96. How can we make sure that a code segment gets executed even in case of uncatched exceptions ?

Ans. By putting it within finally.

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Q97. What is "super" used for ?

Ans. Used to access members of the base class.

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Q98. What is "this" keyword used for ?

Ans. Used to represent an instance of the class in which it appears.

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Q99. Difference between Serialization and Deserialization ?

Core Java

Ans. Serialization is the process of writing the state of an object to a byte stream. Deserialization is the process of restoring these objects.

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Q100. What is an Enum type ?

Core Java

Ans. An enum type is a special data type that enables for a variable to be a set of predefined constants

Sample Code for enum

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