10 Abstract Shape As Well As Interface Interview Questions Answers Inwards Java

Abstract shape too interface are rattling pop inwards whatever object oriented programming linguistic communication or Java interview, too in that location are e'er i or to a greater extent than questions from this. The an interface is more common, because of its popularity with designers but questions from abstract shape also pops upwards at nowadays too then. Interview questions from abstract shape are to a greater extent than mutual on junior grade or y'all say nether ii years sense of  Java programmers land interface-related questions are generally asked on senior grade Java interview e.g. four or vi years of experience. They are generally asked along with other Java blueprint pattern questions, e.g. Decorator pattern or Factory pattern.

Any way, inwards this article nosotros volition run across mix of these interview questions from abstract shape too interface. All questions has been asked inwards diverse Java interviews too difficulty grade for these inquiry is slow for most of Java developer. 

It’s generally fact-based questions, but roughly questions similar difference betwixt abstract shape too interface inwards Java, too when to prefer abstract shape over interface tin dismiss live on actually tricky.

Frequently asked Abstract shape too Interface questions inwards Java

Here is my listing of questions, this non solely explains rules related to abstract shape but also shares roughly tricky questions close using abstract shape too interface. If y'all lead keep asked whatever inquiry on this topic, which y'all don’t run across inwards this list, too then delight part with us equally comment

1) Can abstract shape lead keep constructors inwards Java?

Yes, abstract shape tin dismiss declare too define constructor inwards Java. Since y'all tin dismiss non create trial of abstract class,  constructor tin dismiss solely live on called during constructor chaining, i.e. when y'all create trial of concrete implementation class. 

Now roughly interviewer, enquire what is the role of constructor, if y'all tin dismiss non instantiate abstract class? Well, it tin dismiss even thus live on used to initialize mutual variables, which are declared within abstract class, too used yesteryear diverse implementation. 

Also fifty-fifty if y'all don’t supply whatever constructor, compiler volition add default no statement constructor in an abstract class, without that your subclass volition non compile, since commencement statement inwards whatever constructor implicitly calls super(), default super shape constructor inwards Java.

2) Can abstract shape implements interface inwards Java? does they require to implement all methods?

Yes, abstract shape tin dismiss implement interface yesteryear using implements keyword. Since they are abstract, they don’t demand to implement all methods. It’s proficient practise to supply an abstract base of operations class, along with an interface to declare Type. One instance of this is java.util.List interface too corresponding java.util.AbstractList abstract class. Since AbstractList implements all mutual methods,  concrete implementations like LinkedList too ArrayList are complimentary from burden of implementing all methods, had they implemented List interface directly. It’s best of both world, y'all tin dismiss teach payoff of interface for declaring type, too flexibility of abstract shape to implement mutual conduct at i place. Effective Java has a prissy chapter on how to occupation interface too abstract shape inwards Java, which is worth reading.

3) Can abstract shape live on terminal inwards Java?

No, abstract shape tin dismiss non live on terminal inwards Java. Making them terminal volition halt abstract shape from beingness extended, which is the solely means to occupation abstract class. They are also reverse of each other, abstract keyword enforces to extend a class, for using it, on the other hand, final keyword prevents a shape from beingness extended. In existent footing also, abstract signifies incompleteness, land terminal is used to demonstrate completeness. Bottom occupation is, y'all tin dismiss non brand your shape abstract too final inwards Java, at same time, it’s a compile fourth dimension error.

4) Can abstract shape lead keep static methods inwards Java?

Yes, abstract shape tin dismiss declare too define static methods, nothing prevents from doing that. But, y'all must follow guidelines for making a method static inwards Java, equally it’s non welcomed inwards a object oriented design, because static methods tin dismiss non live on overridden inwards Java. It’s rattling rare, y'all run across static methods within abstract class, but equally I said, if y'all lead keep rattling proficient argue of doing it, too then zero stops you.

5) Can y'all create trial of abstract class?

No, y'all tin dismiss non create trial of abstract shape inwards Java, they are incomplete. Even though, if your abstract shape don’t comprise whatever abstract method, y'all tin dismiss non create trial of it. By making a shape abstract,  you told compiler that, it’s incomplete too should non live on instantiated. Java compiler volition throw error, when a code tries to instantiate abstract class.

6) Is it necessary for abstract shape to lead keep abstract method?

No, It’s non mandatory for an abstract shape to lead keep whatever abstract method. You tin dismiss brand a shape abstract inwards Java, yesteryear only using abstract keyword inwards shape declaration. Compiler volition enforce all structural restriction, applied to abstract class, e.g. at nowadays allowing to create whatever instance. By the way, it’s debatable whether y'all should lead keep abstract method within abstract shape or interface. In my opinion, abstract shape should lead keep abstract methods, because that’s the commencement matter programmer assumes, when he run across that class. That would also teach nicely along regulation of to the lowest degree surprise.

7) Difference betwixt abstract shape too interface inwards Java?

This is the most of import too i of the classic Java Interview question. I don’t know, how many times I lead keep seen this inquiry at all most all levels of Java interviews. One reason, which makes this inquiry interesting is mightiness to arrive at example. It’s slow to answers questions on centre OOPS concepts like Abstraction, Encapsulation, Polymorphism and Inheritance, but when it comes to subtle points similar this, candidate to a greater extent than oft fumbled. You tin dismiss run across this post service for all syntactical deviation betwixt abstract shape too interface, but it deserve a post service on it’s own.

8) When do y'all favor abstract shape over interface?

This is the follow-up of previous interview questions on abstract shape too interface. If y'all know syntactical difference, y'all tin dismiss reply this inquiry quite easily, equally they are the one, which drives the decision. Since it’s almost impossible to add together a novel method on a published interface, it’s amend to occupation abstract class, when development is concern. Abstract shape inwards Java evolves amend than interface. Similarly, if y'all lead keep besides many methods within interface, y'all are creating hurting for all it’s implementation, consider providing an abstract shape for default implementation. This is the pattern followed inwards Java collection package, y'all tin dismiss run across AbstractList provides default implementation for List interface.

9) What is abstract method inwards Java?

An abstract method is a method without body. You only declare method, without defining it too occupation abstract keyword inwards method declaration.  All method declared inside Java Interface are yesteryear default abstract. Here is an instance of abstract method inwards Java

                public void abstract printVersion();

Now, In lodge to implement this method, y'all demand to extend abstract shape and override this method.

10) Can abstract shape contains primary method inwards Java ?

Yes, abstract shape tin dismiss contain main method, it only another static method too y'all tin dismiss execute Abstract shape with primary method, until y'all don’t create whatever instance.

That’s all on this list of interview questions on abstract class, interface too methods inwards Java. You tin dismiss also bookmark this listing equally FAQ for abstract class, prissy to refresh, earlier going to interview. On dissimilar note, abstract shape too interface are cardinal blueprint decisions on object oriented analysis too blueprint process, too should live on taken yesteryear applying due diligence, of course of report if y'all desire to write flexible systems.

Further Learning
SOLID Principles of Object Oriented Design
Absolute Introduction to Object Oriented Programming inwards Java
Java - Object Oriented Programming [For Absolute Beginners]