Abstract class in java

An abstract class is the class which is declared abstract and can have abstract or non abstract methods. An abstract class can not be instantiated. It can be extended by subclass to implement abstract methods and either use or override concrete methods.

Abstract method in java

Abstract method is the method which do not have implementation i.e. it does not have anybody.

When do you need abstract class in java?

Let’s understand it with the help of the example. You have Shape class and it has some methods such as draw(), calcualteArea() etc. Drawing a shape is common for all the shapes but calculateArea() is different for each shape.

For example:

For Rectangle, it will be calculated as length * breadth and for circle, it will be pi* radius^2.

So with above behavior, we will implement draw() method in shape class and will create calcualteArea() as abstract method.So if you have some common behaviors and some specific behavior, make your class abstract.

Let’s create a abstract class as Shape and Rectangle, Circle class as concrete classes.

Example of Abstract class in java:

Create a main class named “AbstractClassMain”
============================
Draw method in shape class
Area of rectangle is 12.0
============================
Draw method in shape class
Area of circle is 28.259999999999998
============================

Let’s consider some cases to understand abstract class in java better:
Case 1: Is is possible to have zero abstract method in class but still you can declare class as abstract.
Answer:
Yes, It is possible to declare class as abstract even if you don’t have any abstract method in the class.
For example:

public void draw() { System.out.println(“Draw method in shape class”); } }

Case 2: Class contains abstract method but is it possible to not declare class as Abstract?
Answer:
No, It is mandatory to declare class as Abstract but it contain abstract method.

You will get compilation errors:

  • At line 1 : “The type Shape must be an abstract class to define abstract methods”
  • At line 7: “The abstract method calculateArea in type Shape can only be defined by an abstract class”

If you have abstract method in class, class must be declared as abstract class in java

Case 3: Can you declare class as final and abstract at the same time?

Answer:

No, you can not declare class as final and abstract at the same time. Final means No other class can extend that class and Abstract means Class must be extended by any other class.

Case 4: Can you instantiate abstract class in java?

Answer:

No, you can not instantiate abstract class.

You can not instantiate abstract class in java

Case 5: If you are extending an abstract class in java, do you need to implement all the abstract methods of that class?

Answer:

Yes, you need to implement all the abstract method of superclass unless and until subclass is also an abstract class in java.

That’s all about abstract class in java.

Related Posts

  • Compare date in SQL
    08 October

    How to Compare Dates in SQL

    Table of ContentsAgendaIntroduction to DATE in SQLComparing Dates in SQL with ExamplesUsing Comparison OperatorsUsing the BETWEEN ClauseComparing Dates for DATETIME Datatypes/FormatsUsing Comparison Operator with TimeStampCasting DATETIME as DATE without TimestampUsing Between Clause with DATETIME Agenda This article will look at yet another interesting topic in SQL commonly asked in interviews – How to Compare Dates […]

  • Get Number of Elements in Array in C++
    08 October

    Get Number of Elements in Array in C++

    Table of ContentsGet Number of Elements in Array in C++Using the sizeof() functionUsing the pointersUsing the size() functionGet the frequency of each element in array in C++Using nested for loopUsing maps One of the most fundamental collections in any programming language is an array. It stores a similar type of data at specific indices that […]

  • can you screenshot onlyfans
    08 October

    Can You Screenshot OnlyFans? Here is Everything You Need to Know

    Table of ContentsOnlyFans: A Brief IdeaCan You Screenshot OnlyFans?Can You Screenshot OnlyFans Without Getting Banned?Can You Screenshot OnlyFans Without Them Knowing: Screenshot NotificationsFrequently Asked Questions About: Can You Screenshot OnlyFans?What Happens When You Try Taking OnlyFans Screenshots?Is Screenshotting Illegal?Do the OnlyFans screenshots lead to a permanent account ban?Can OnlyFans screenshots be detected?Wrapping Up Can you […]

  • Trust browser enable
    08 October

    How to enable trust wallet browser

    Table of ContentsTrust DApp Browser: A Brief OverviewWhat are DApps on Trust Wallet?Access DApps Using Trust Wallet: Easiest ApproachTrust Browser Enable on Android: How to Activate/Enable DApp Browser on Trust WalletTrust Browser Enable on iOS: How to Activate/Enable DApp Browser on Trust Wallet#Method 1: “Trust Browser Enable” Procedure#Method 2: Enabling DApp by Visiting Pancake SwapFrequently […]

  • how-to-find-someone-on-onlyfans
    07 October

    How to Find Someone on OnlyFans: Working Methods

    Table of ContentsHow to Find Someone on OnlyFansHow to Find Someone on OnlyFansHow to Find Someone on OnlyFans: The Official Username MethodThe OnlyFans TrickHow to Find Someone on OnlyFans: The Email MethodHow to Find Someone on OnlyFans: The OnlyFinder MethodHow to Find Someone on OnlyFans By Location (Map Feature)How to Find Someone on OnlyFans By […]

  • How to delete snapchat messages the other person saved
    07 October

    How to delete snapchat messages the other person saved

    Table of ContentsHow to delete Snapchat messages the other person saved#Step 1: Log in to Your Snapchat Account#Step 2: Navigate to the Desired Chat#Step 3: Unsave The Message from Your End#Step 4: Long-Press and Delete the Message#Step 5: Proceed with the Learn More option#Step 6: Click Okay#Step 7: Tap on the option that says “Delete.”How […]

Leave a Reply

Your email address will not be published. Required fields are marked *

Subscribe to our newletter

Get quality tutorials to your inbox. Subscribe now.