10 Abstract Flat As Well As Interface Interview Questions Answers Inward Java

Abstract degree as well as interface are really pop inwards whatever object oriented programming linguistic communication or Java interview, as well as in that location are ever i or to a greater extent than questions from this. The an interface is more common, because of its popularity amidst designers but questions from abstract degree also pops upward at nowadays as well as then. Interview questions from abstract degree are to a greater extent than mutual on junior aeroplane or you lot say nether ii years sense of  Java programmers spell interface-related questions are generally asked on senior aeroplane Java interview e.g. four or half-dozen years of experience. They are generally asked along alongside other Java pattern 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 degree as well as interface. All questions has been asked inwards diverse Java interviews as well as difficulty aeroplane for these interrogation is slow for most of Java developer. 

It’s generally fact-based questions, but roughly questions similar difference betwixt abstract degree as well as interface inwards Java, as well as when to prefer abstract degree over interface tin endure actually tricky.

Frequently asked Abstract degree as well as Interface questions inwards Java

Here is my listing of questions, this non entirely explains rules related to abstract degree but also shares roughly tricky questions most using abstract degree as well as interface. If you lot direct keep asked whatever interrogation on this topic, which you lot don’t run across inwards this list, thence delight portion alongside us every bit comment

1) Can abstract degree direct keep constructors inwards Java?

Yes, abstract degree tin declare as well as define constructor inwards Java. Since you lot tin non create instance of abstract class,  constructor tin entirely endure called during constructor chaining, i.e. when you lot create instance of concrete implementation class. 

Now roughly interviewer, inquire what is the role of constructor, if you lot tin non instantiate abstract class? Well, it tin withal endure used to initialize mutual variables, which are declared within abstract class, as well as used yesteryear diverse implementation. 

Also fifty-fifty if you lot don’t render whatever constructor, compiler volition add default no statement constructor in an abstract class, without that your subclass volition non compile, since get-go statement inwards whatever constructor implicitly calls super(), default super degree constructor inwards Java.

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

Yes, abstract degree tin implement interface yesteryear using implements keyword. Since they are abstract, they don’t demand to implement all methods. It’s adept practise to render an abstract base of operations class, along alongside an interface to declare Type. One instance of this is java.util.List interface as well as corresponding java.util.AbstractList abstract class. Since AbstractList implements all mutual methods,  concrete implementations like LinkedList as well as ArrayList are costless from burden of implementing all methods, had they implemented List interface directly. It’s best of both world, you lot tin larn payoff of interface for declaring type, as well as flexibility of abstract degree to implement mutual conduct at i place. Effective Java has a prissy chapter on how to usage interface as well as abstract degree inwards Java, which is worth reading.

3) Can abstract degree endure finally inwards Java?

No, abstract degree tin non endure finally inwards Java. Making them finally volition halt abstract degree from existence extended, which is the entirely means to usage abstract class. They are also contrary of each other, abstract keyword enforces to extend a class, for using it, on the other hand, final keyword prevents a degree from existence extended. In existent globe also, abstract signifies incompleteness, spell finally is used to demonstrate completeness. Bottom describe of piece of occupation is, you lot tin non brand your degree abstract as well as final inwards Java, at same time, it’s a compile fourth dimension error.

4) Can abstract degree direct keep static methods inwards Java?

Yes, abstract degree tin declare as well as define static methods, nothing prevents from doing that. But, you lot must follow guidelines for making a method static inwards Java, every bit it’s non welcomed inwards a object oriented design, because static methods tin non endure overridden inwards Java. It’s really rare, you lot run across static methods within abstract class, but every bit I said, if you lot direct keep really adept argue of doing it, thence aught stops you.

5) Can you lot create instance of abstract class?

No, you lot tin non create instance of abstract degree inwards Java, they are incomplete. Even though, if your abstract degree don’t comprise whatever abstract method, you lot tin non create instance of it. By making a degree abstract,  you told compiler that, it’s incomplete as well as should non endure instantiated. Java compiler volition throw error, when a code tries to instantiate abstract class.

6) Is it necessary for abstract degree to direct keep abstract method?

No, It’s non mandatory for an abstract degree to direct keep whatever abstract method. You tin brand a degree abstract inwards Java, yesteryear only using abstract keyword inwards degree 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 you lot should direct keep abstract method within abstract degree or interface. In my opinion, abstract degree should direct keep abstract methods, because that’s the get-go affair programmer assumes, when he run across that class. That would also larn nicely along regulation of to the lowest degree surprise.

7) Difference betwixt abstract degree as well as interface inwards Java?

This is the most of import as well as i of the classic Java Interview question. I don’t know, how many times I direct keep seen this interrogation at all most all levels of Java interviews. One reason, which makes this interrogation interesting is might to arrive at example. It’s slow to answers questions on gist 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 run across this ship service for all syntactical deviation betwixt abstract degree as well as interface, but it deserve a ship service on it’s own.

8) When do you lot favor abstract degree over interface?

This is the follow-up of previous interview questions on abstract degree as well as interface. If you lot know syntactical difference, you lot tin reply this interrogation quite easily, every bit 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 ameliorate to usage abstract class, when development is concern. Abstract degree inwards Java evolves ameliorate than interface. Similarly, if you lot direct keep also many methods within interface, you lot are creating hurting for all it’s implementation, consider providing an abstract degree for default implementation. This is the pattern followed inwards Java collection package, you lot tin 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 as well as usage 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 guild to implement this method, you lot demand to extend abstract degree and override this method.

10) Can abstract degree contains primary method inwards Java ?

Yes, abstract degree tin contain main method, it only another static method as well as you lot tin execute Abstract degree alongside primary method, until you lot don’t create whatever instance.

That’s all on this list of interview questions on abstract class, interface as well as methods inwards Java. You tin also bookmark this listing every bit FAQ for abstract class, prissy to refresh, earlier going to interview. On unlike note, abstract degree as well as interface are fundamental pattern decisions on object oriented analysis as well as pattern process, as well as should endure taken yesteryear applying due diligence, of course of report if you lot 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]

Share this post