abstract-class.md

Abstract Class

Java Abstract Class

In Java, abstract classes and methods facilitate abstraction, allowing developers to hide implementation details and focus on essential information. Here's a summarized overview:

1. Abstract Class:

   • Abstract classes in Java cannot be instantiated; we use the abstract keyword to declare them.
   • Abstract classes can have both regular methods and abstract methods (methods without a body).
   • If a class contains an abstract method, the class itself must be declared as abstract.

   // Example: Abstract Class
   abstract class Language {
     abstract void method1();
   
     void method2() {
       System.out.println("This is a regular method");
     }
   }

2. Abstract Method:

   • Abstract methods define a method signature without providing the implementation.
   • If a class has abstract methods, all its subclasses must implement these methods.

   // Example: Abstract Method
   abstract void display();

3. Creating Subclasses:

   • Subclasses can be created from abstract classes.
   • Members of the abstract class can be accessed using objects of the subclass.

   // Example: Subclass and Accessing Members
   abstract class Language {
     public void display() {
       System.out.println("This is Java Programming");
     }
   }
   
   class Main extends Language {
     public static void main(String[] args) {
       Main obj = new Main();
       obj.display(); // Output: This is Java Programming
     }
   }

4. Implementing Abstract Methods:

   • Subclasses must provide implementations for all abstract methods of the abstract superclass.

   // Example: Implementing Abstract Methods
   abstract class Animal {
     abstract void makeSound();
   
     public void eat() {
       System.out.println("I can eat.");
     }
   }
   
   class Dog extends Animal {
     public void makeSound() {
       System.out.println("Bark bark");
     }
   }
   

5. Accessing Abstract Class Constructors:

   • Abstract classes can have constructors, and their constructors can be accessed using the super keyword in the subclass constructor.

   // Example: Accessing Abstract Class Constructors
   abstract class Animal {
     Animal() {
       // Constructor logic
     }
   }
   
   class Dog extends Animal {
     Dog() {
       super(); // Accessing abstract class constructor
       // Subclass constructor logic
     }
   }
   

6. Java Abstraction:

   • Abstraction involves hiding unnecessary details and showing only essential information.
   • Abstract classes and methods are key to achieving abstraction in Java.

   // Example: Java Abstraction
   abstract class MotorBike {
     abstract void brake();
   }
   
   class SportsBike extends MotorBike {
     public void brake() {
       System.out.println("SportsBike Brake");
     }
   }
   
   class MountainBike extends MotorBike {
     public void brake() {
       System.out.println("MountainBike Brake");
     }
   }

7. Key Points:

   • Use the abstract keyword for abstract classes and methods.
   • Abstract methods don't have implementations.
   • Abstract classes cannot be instantiated.
   • Subclasses inherit and provide implementations for abstract methods.
   • Constructors of abstract classes can be accessed using super in subclasses.
   • Abstraction helps manage complexity by focusing on high-level ideas.