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

Core Java - Interview Questions and Answers for 'Abstract' - 40 question(s) found - Order By Rating

Q1. Interface vs Abstraction

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Q2. Does abstract class have public constructor?

Core Java

Ans. Yes, an abstract class can have a constructor in Java.

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Q3. Difference between Base Class, Derived Class , Abstract Class and Concrete Class ?

Core Java

Ans. Base Class is a relative term used to signify the Parent class in Parent - Child or Base - derived relationship.

Derived Class is a relative term used to signify the Child class in Parent - Child or Base - derived relationship.

Abstract Class is a class that is not allowed to be instantiated and hence can serve only a base class for it's usage.

Concrete Class is the class which is supposed to be instantiated and hence provide definition for all implementing interface methods and extending abstract methods.

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Q4. Can an abstract class be a derived class ?

Core Java

Ans. Yes, an abstract class can extend another class.

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Q5. What is the relationship between Base Class and Abstract Class ?

Core Java

Ans. Abstract Class is a class that's only allowed to be a Base class for it's usage. It can never be instantiated on it's own.

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Q6. Can we declare an Interface with abstract keyword ?

Core Java

Ans. Yes

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Q7. Can we have multiple inheritance in java using abstract class ?

Core Java

Ans. No

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Q8. how does abstraction help your application ?

Core Java

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Q9. What is abstraction ?

Design

Ans. Abstraction is a process of hiding the implementation details and describing only the functionality to the user.

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Q10. What are the advantage of Abstract classes over interfaces with respect to Java 7 ? and What changed in Java 8 to help facilitate that in Java 8 ?

Core Java

Ans. Abstract Classes provide default implementations of methods that are inherited by the classes that extend them, which was not the case for Interfaces. This changed in Java 8, where default implementations are provided for methods.

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Q11. What are the uses of Abstraction ?

Core Java

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

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Q12. If an Abstract class has only abstract methods, What's the difference between such a class and an interface ?

Core Java

Ans. Such a class still can have member elements which can be inherited and hence facilitate code reuse. Moreover Abstract class can have non final static elements whereas interfaces are only allowed to have static final elements.

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Q13. What is the importance of Abstract Class ?

Core Java

Ans. Abstract classes provide a mechanism of interfacing ( using abstract method ) as well as code reuse through inheritance ( extending abstract class )

Comparing to concrete class they have an advantage of providing interface which a concrete class doesn't provide.

Comparing to interfaces they have an advantage of providing code reuse through inheritance which interfaces dont provide.

Sample Code for abstract class

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Q14. Why can't we create an instance of abstract class ? Why is it restricted by compiler ?

Core Java

Ans. Because Abstract class is incomplete i.e there are abstract methods that needs to be defined by extending classes.

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Q15. What was the need of creating an abstract class in Java when we cannot instantiate an object of it ?

Core Java

Ans. The objective of an abstract class is to provide an interface as well as code reuse. Though we cannot instantiate an instance of abstract class but we can reuse the code by extending such a class. Moreover abstract class provides interfacing to outside components just like interfaces.

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Q16. Can we override an abstract method with abstract method in the derived class ?

Core Java

Ans. Yes, but in that case the derived class itself should be abstract. We cannot have an object of a class without definition for the method which has been declared abstract in the parent.

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Q17. Can we override abstract methods ?

Core Java

Ans. Abstract methods are the methods that need to be overridden in the derived class ( either as implementing method or again abstract method ) so it's not only allowed but its required to override abstract method in the derived class.

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Q18. Can we overload abstract methods ?

Core Java

Ans. Yes

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Very frequently asked. Usually asked in this format or as difference with interfaces / concrete classes.

Q19. What is an abstract class ?

Core Java

Ans. Abstract class is the class that is not supposed to be instantiated. The purpose of the class to only have extension to the derived class.

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Q20. When should we use Abstract classes ?

Core Java

Ans. Abstract classes provide a mechanism of interfacing ( using abstract method ) as well as inheritance ( extending abstract class ). So they should be used in place of interfaces in case there is some code ( methods ) or object body ( member elements ) that can be reused with inheritance.

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Q21. Can we declare a main method as abstract ?

Ans. No. Static methods cannot be overridden and hence make no sense to be declared abstract.

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Q22. Can you give a real world example of Encapsulation and Abstraction ?

Core Java

Ans. Car Engine is an example of encapsulation and abstraction. You ignite the car using an interface called starter and least bothered about how the tire actually moves (This is abstraction). The engine encapsulates the complete process to itself only and doesn't allow you to start the other components like the radiator etc ( this is excapsulation )

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Very frequently asked to Fresh graduates.

Q23. 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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Q24. 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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Q25. Difference between Factory and Abstract Factory Design Pattern ?

Design

Ans. Factory Pattern deals with creation of objects delegated to a separate factory class whereas Abstract Factory patterns works around a super-factory which creates other factories.

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Q26. Can we declare an abstract method private ?

Ans. No Abstract methods can only be declared protected or public.

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Q27. What are the design considerations while making a choice between using interface and abstract class ?

Core Java

Ans. Keep it as a Abstract Class if its a "Is a" Relationsship and should do subset/all of the functionality. Keep it as Interface if its a "Should Do" relationship.

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Q28. Difference between Abstraction and Implementation hiding ?

Ans. Implementation Hiding is a broader concept. Abstraction is a way of implementation hiding in OOP's.

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Q29. What are the examples of Abstraction in Java ?

Ans. function calling - hides implementation details
wrapper classes
new operator - Creates object in memory, calls constructor

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Q30. what will be the output ?

class Animal {
public void eat() throws Exception {
}
}

class Dog2 extends Animal {
public void eat(){}
public static void main(){
Animal an = new Dog2();
an.eat();
}
}

Core Java

Ans. Compile Time Error: Unhandled exception type Exception

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