Abstract Classes

Concrete Class	Abstract Class
Regular class	Class that uses `abstract` keyword
Objects can be created	Objects cannot be created
Reference can be created	Reference can be created

abstract class Base {
    Base() {
        System.out.println("Base Constructor");
    }

    void method1() {
        System.out.println("Method 1 called");
    }

    abstract void method2();
}

class Derived extends Base {
    void method2() {
        System.out.println("Method 2 called");
    }
}

public class Main {
    public static void main(String[] args) {
        // Reference of abstract class is allowed
        Base b;
        
        // Reference and object of concrete class is allowed
        Derived d = new Derived();
    }
}

Abstract Method

Method which is not having a body is known as Abstract method, and the method must be declared as abstract.

The abstract method is undefined method.

Abstract Class

A class is Abstract class if at least one of the methods is abstract, and we has to declare that class as abstract.

Though, already declared abstract class is allowed to not contain any abstract method.

Inheriting from abstract class

If any other class inherits abstract class then that class also becomes abstract class...

but to make the subclass as concrete class it must override all the abstract methods.

Abstract Class and abstract methods, can neither be final nor static.

Abstract Classes are used for implementing Inheritance as well as Polymorphism.
- Inheritance: using Concrete Methods
- Polymorphism: using Abstract Methods

Last modified: 08 February 2026