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

Core Java - Interview Questions and Answers for 'Abstract classe' - 7 question(s) found - Order By Rating

Q1. 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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Q2. 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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Q3. 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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Q4. 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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Q5. Will this Code compile ?

abstract public class BuggyBread1{
abstract public void test(){};
}

Core Java

Ans. No. This will give a compilation error saying "Abstract methods do not specify a body".

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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.

Q6. 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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Q7. In the following code , how many methods needs to be implemented in Class B ?

public interface A{
   public void method1();
   public void method2();
   public void method3();
}

abstract class B implements A{
}

Core Java

Ans. As Class B has been declared abstract , we can either implement any of these methods and just declare rest of them abstract.

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