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Q151. Difference between multiple and multi level inheritance ?

Ans. Multiple Inheritance refers to the concept of a class inheriting multiple classes. Example - Class C extends Class A ,Class B. This is not allowed in Java.

Multilevel Inheritance refers to the concept of Inheritance in a chain. Example - Class B extends Class A, Class C extends Class B. This is permitted in Java.

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Q152. Can you name some of the Java frameworks in different domains ?

Ans. Web Framework - Spring , Struts, Play
Dependency Injection frameworks - Google Guice , PicoContainer and Dagger
ORM Framework - Hibernate
Big Data / ETL Frameworks - Apche Hadoop , Apache Crunch, Apache Spark.
View Frameworks - JSF , Apache Wicket,jtwig.
Java Gui Frameworks - SWT , AWT, JavaFX
Testing - Junit, Mockito, PowerMock, EasyMock, JMock, JMockit
Rest Web services - Jersey , Restlet , RestX, RestEasy ,Restfulie

Here is the big list for reference - http://javasearch.buggybread.com/home2.php?keyword=

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Q153. What are the core OOPs concepts ?

Ans. Abstraction, Encapsulation, Polymorphism , Composition and Inheritance

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Q154. How are the concept of Association related to Composition and Inheritance ?

Ans. Composition and Inheritance are the different types of Associations for Classes.

Composition is a has-a association between classes.
Inheritance is a is-a association between classes.

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Q155. how many reducer task runs on a hadoop cluster ?

Ans. Generally one reducer runs for all mappers, but it can be increased as per requirements.

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Q156. Is it a good design practice to have programming constructs like if and loops in constructor ?

Ans. I would avoid that. If we need to initialize member elements differently on the basis of some condition, I would prefer having overloaded constructors. I don't see a need to have a loop for initializing member elements unless the count of elements is huge and they all need to be initialized with common value.

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Q157. What are the counter controlled repetitions in java ?

Ans. Counter controlled repetitions are the loops that are controlled with the use of counters or the loops where the number of repetitions are known in advance. for loop in java is the counter controlled repetition.

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Q158. Which of the two - compile time and run time polymorphism - requires signature of the method to be different ?

Ans. runtime polymorphism or method overriding doesn't require method name and signature to be different whereas compile time polymorphism or method overloading requires method name to be same but the signature to be different.

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Q159. What is "dynamic method dispatch" in java ?

Ans. dynamic method dispatch is a process in which a call to an
overridden method is resolved at runtime rather than at compile-time. This is used to achieve runtime polymorphism in java.

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Q160. How do you take screenshot in selenium?

Ans. TakeScreenshot th = TakeScreenshot(driver); //Enable the driver object to take screenshot

File src = th.getScreenShotAs(OutputType.FILE);

FileUtils.copyFilesrc("locationWhereUWantToPlaceTheScreenshot.jpg");

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Q161. What is dynamic dispatch in Java ?

Ans. Dynamic dispatch in java is also known as runtime polymorphism.It is a process in which a call to an overriden method is resolved at runtime.

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Q162. What happens to private variables during inheritance ?

Ans. Private variables are not inherited. They are simply ignored and not made part of the derived object body.

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Q163. How can we hide a class in Java ?

Ans. By encapsulating it within another class and declaring it private. In such a case, it will only be accessible through parent class or parent class object.

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Very frequently asked. Usually among very first few questions.

Q164. Define encapsulation in Java ?

Ans. Encapsulation is a feature of OOP's that binds the data and it's associated methods together as a single unit and facilitate protection and data hiding by providing minimal interface to outside. For example - member variables are declared private and are accessed through public methods. Moreover we have private methods that can only be used internally and hence providing minimal interface to outside class through use of public methods.

Sample Code for encapsulation

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Q165. Give an example of how Object Oriented Programming Concepts can be implemented.

Ans. You can implement encapsulation in Java by keeping the fields (class variables) private and providing public getter and setter methods to each of them. Java Beans are examples of fully encapsulated classes. Encapsulation in Java: Restricts direct access to data members (fields) of a class.

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Q166. What are the different types of loops in Java ?

Ans. for, while and do while

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Q167. What is an infinite loop ?

Ans. Infinite loop is a programming condition wherein the control goes into an infinite loop because the loop termination condition can never be met. For example -

for(int x=1;x>0;x++){
}

in this loop, with each increment the condition x > 0 will remain true till infinity.

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Q168. Explain Inheritance and Polymorphism.

Ans. Getting parent class object properties into child class is called Inheritance.

The process of representing one form into multiple forms is called polymorphism.

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Q169. What is the difference between return and continue statement ?

Ans. return is used within a method to return control out of the method. It may be followed by a value which is returned from the method to calling method immediately preceding the point of call.

continue statement is used within a loop to start next iteration without executing the remaining statements in the loop.

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Q170. What are the uses of Abstraction ?

Ans. Loose Coupling
Facilitates designing complex applications by making them modular.

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Q171. Which of the OOP's features facilitate dependency injection ?

Ans. Inheritance , Runtime Polymorphism and Composition.

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Q172. Is Runtime Polymorphism possible without Inheritance ?

Ans. Yes, Runtime Polymprohism requires either Class inheritance or Interface implementation.

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Q173. Why Java is considered more purer object oriented language than C++ ?

Ans. Because of

lack of use of pointers,
Lack of structural programming and
Lack of Multiple Inheritance

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Q174. Why shouldn't we use string concatenation extensively or in a loop ?

Ans. Because String being an immutable object creates a new object upon each concatenation cycle. If there is any such need , we should use String Builder whose objects are mutable.

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Q175. how does abstraction help your application ?

^{This question was recently asked at 'Intel'.This question is still unanswered. Can you please provide an answer.}

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Q176. Explain OOps concepts.

Ans. There are four main OOP concepts in Java. These are:

Abstraction. Abstraction means using simple things to represent complexity. We all know how to turn the TV on, but we don?t need to know how it works in order to enjoy it. In Java, abstraction means simple things like objects, classes, and variables represent more complex underlying code and data. This is important because it lets avoid repeating the same work multiple times.

Encapsulation. This is the practice of keeping fields within a class private, then providing access to them via public methods. It?s a protective barrier that keeps the data and code safe within the class itself. This way, we can re-use objects like code components or variables without allowing open access to the data system-wide.

Inheritance. This is a special feature of Object Oriented Programming in Java. It lets programmers create new classes that share some of the attributes of existing classes. This lets us build on previous work without reinventing the wheel.

Polymorphism. This Java OOP concept lets programmers use the same word to mean different things in different contexts. One form of polymorphism in Java is method overloading. That?s when different meanings are implied by the code itself. The other form is method overriding. That?s when the different meanings are implied by the values of the supplied variables. See more on this below.

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Q177. What is composition ?

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Sample Code for composition

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Q178. What is Overriding ?

Ans. Overriding refers to the Methods with same name and parameters, such that the later over rides the former method.

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Q179. What are the characteristics of the object ?

Ans. 1. State

Instance variable or member elements forms the object state.

2. Behavior

Member functions forms the object behavior

3. Identity

Every object has a unique identity within JVM through a unique Id.

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Q180. Which of the OOP's feature - encapsulation or abstraction - is more important ?

Ans. Encapsulation facilitates security by hiding data and logic whereas Abstraction simplifies organization of data and related logic.

As applications scale, both concepts are required for easy management and maintenance. Encapsulation for security and criss cross communication between objects / modules will make it vulnerable. and Abstraction for better organization that enables better understanding of application code and easy maintainability.

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