Core Java - Interview Questions and Answers for 'Basic' | Search Interview Question

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Q181. What is URL?

Java EE

Ans. URL is Uniform Resource Locator which is representation of HTTP address.

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Q182. 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.

Q183. What is the difference between Encapsulation and Abstraction?

Core Java

Ans. 1.Abstraction solves the problem at design level while encapsulation solves the problem at implementation level

2.Abstraction is used for hiding the unwanted data and giving relevant data. while Encapsulation means hiding the code and data into a single unit to protect the data from outside world.

3. Abstraction lets you focus on what the object does instead of how it does it while Encapsulation means hiding the internal details or mechanics of how an object does something.

4.For example: Outer Look of a Television, like it has a display screen and channel buttons to change channel it explains Abstraction but Inner Implementation detail of a Television how CRT and Display Screen are connect with each other using different circuits , it explains Encapsulation.

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Q184. Explain static blocks in Java ?

Core Java

Ans. A static initialization block is a normal block of code enclosed in braces, { }, and preceded by the static keyword. Here is an example:

static {
// whatever code is needed for initialization goes here
}

A class can have any number of static initialization blocks, and they can appear anywhere in the class body. The runtime system guarantees that static initialization blocks are called in the order that they appear in the source code.

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Q185. 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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Q186. Explain Annotations ?

Ans. Annotations, a form of metadata, provide data about a program that is not part of the program itself. Annotations have no direct effect on the operation of the code they annotate. Annotations have a number of uses, among them:
â€¢ Information for the compiler â€” Annotations can be used by the compiler to detect errors or suppress warnings.
â€¢ Compile-time and deployment-time processing â€” Software tools can process annotation information to generate code, XML files, and so forth.
â€¢ Runtime processing â€” Some annotations are available to be examined at runtime.

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Q187. Difference between Abstract and Concrete Class ?

Core Java

Ans. Abstract classes are only meant to be sub classed and not meant to be instantiated whereas concrete classes are meant to be instantiated.

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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.

Q188. 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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Q189. Difference between Vector and ArrayList ?

Core Java

Ans. Vectors are synchronized whereas Array lists are not.

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Q190. 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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Frequently asked in Cognizant (CTS)

Q191. What is Serialization ? Why do we need it ?

Core Java

Ans. Storing the state of an object in a file or other medium is called serialization.

Classes can communicate only if they are built together ( as they need Byte code for communication ). What if we need to enable communication between different applications ( i.e they have been built independently or even they reside at different locations ), We need a mechanism that will transfer the Bean state to a Medium than can be transferred to the receiving application.

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Q192. 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.

Q193. 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

Q194. What is an Immutable Object ?

Core Java

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

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Very Frequently asked. Usually asked along with String Class related questions.

Q195. What is an immutable class ?

Core Java

Ans. Class using which only immutable (objects that cannot be changed after initialization) objects can be created.

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Q196. Name few Java Exceptions ?

Core Java

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

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Frequently asked to fresh graduates and less experienced.

Q197. Which of the following is tightly bound ? Inheritance or Composition ?

Core Java

Ans. Inheritance.

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Q198. 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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Q199. What is "super" used for ?

Ans. Used to access members of the base class.

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Q200. What is "this" keyword used for ?

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

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Q201. Difference between boolean and Boolean ?

Core Java

Ans. boolean is a primitive type whereas Boolean is a class.

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Q202. What is a finalize method ?

Core Java

Ans. finalize() method is called just before an object is destroyed.

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Frequently asked to fresh graduates.

Q203. 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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Frequently asked to fresh graduates.

Q204. 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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Q205. 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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Q206. 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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Q207. 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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Q208. What is a Static import ?

Core Java

Ans. By static import , we can access the static members of a class directly without prefixing it with the class name.

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

Q209. Difference between StringBuffer and StringBuilder ?

Core Java

Ans. StringBuffer is synchronized whereas StringBuilder is not.

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Q210. Difference between Map and HashMap ?

Core Java

Ans. Map is an interface where HashMap is the concrete class.

Sample Code for map

Sample Code for hashmap

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