Abstract class

 Abstract class 

Abstract class in Java

A class which is declared as abstract is known as an abstract class. It can have abstract and non-abstract methods. It needs to be extended and its method implemented. It cannot be instantiated.

Key Concepts:

1. Abstract Class:

   • An abstract class is declared with the abstract keyword (in languages like Java).
   • It cannot be instantiated directly, meaning you cannot create an object of an abstract class.

2. Abstract Methods:

   • An abstract method is a method that is declared without an implementation (no body).
   • It forces subclasses to provide an implementation for this method.
   • Abstract methods are also declared using the abstract keyword.

3. Concrete Methods:

   • These are regular methods with an implementation.
   • An abstract class can have both abstract methods (without implementation) and concrete methods (with implementation).

Purpose of Abstract Class:

1. Design Blueprint:

   • Abstract classes provide a common design for subclasses.
   • They define what methods must be implemented by the subclasses.

2. Code Reusability:

   • You can define common methods in the abstract class, which can be shared across multiple subclasses.
   • This avoids code duplication and promotes reusability.

3. Encapsulation:

   • Abstract classes help in hiding the implementation details and only exposing the essential features.
   • This is part of the OOP principle of encapsulation.

Example in Java:

Here's a simple example to illustrate abstract classes and methods in Java:

// Abstract class
 abstract class Animal {
    // Concrete method
    public void eat() {
        System.out.println("This animal eats food.");
    }

    // Abstract method
    public abstract void makeSound();
}

// Subclass (inherits from Animal)
class Dog extends Animal {
    // Providing implementation for the abstract method
    @Override
    public void makeSound() {
        System.out.println("The dog barks.");
    }
}

// Main class
public class Main {
    public static void main(String[] args) {
        // Animal animal = new Animal(); // This will give an error because you can't instantiate an abstract class

        Animal animal; //declare a reference variable

        animal = new Dog();
        animal.eat();         // Calls the concrete method from the abstract class
        animal.makeSound();   // Calls the implemented abstract method from the subclass
    }
}