---

What is Abstraction?

Abstraction is the process of hiding internal implementation details and showing only the essential features to the user.

Think of it like using a car:
• You use the steering wheel and accelerator…
• But you don’t need to know how the engine or fuel injection system works!

How is Abstraction Achieved in Java?

Java provides two ways to achieve abstraction:

Tool	Description
Abstract Classes	Partial abstraction (can have both abstract and concrete methods)
Interfaces	Full abstraction (Java 8+ allows default methods too)

Abstract Class

An abstract class cannot be instantiated. It may contain abstract methods (no body) and concrete methods (with body).

Syntax:

    
    abstract class Shape {
        abstract void draw();  // abstract method

        void display() {
            System.out.println("Displaying shape...");
        }
    }

    class Circle extends Shape {
                @Override
        void draw() {
            System.out.println("Drawing Circle");
        }
    }
    
    

Usage:

    
    public class Main {
        public static void main(String[] args) {
            Shape s = new Circle();  // Abstract class reference to concrete class
            s.draw();
            s.display();
        }
    }
    
    

Output:

    
    Drawing Circle  
    Displaying shape...
    
    

Interface

An interface is a contract — any class that implements it must provide definitions for all its methods.

Syntax:

    
    interface Animal {
        void makeSound();  // implicitly public and abstract
    }

    class Dog implements Animal {
        public void makeSound() {
            System.out.println("Dog barks");
        }
    }
    
    

Usage:

    
    public class Main {
        public static void main(String[] args) {
            Animal a = new Dog();
            a.makeSound();
        }
    }
    
    

Output:

    
    Dog barks
    
    

Abstract Class vs Interface

Feature	Abstract Class	Interface
Methods	Can have both abstract and normal methods	Only abstract methods (Java 8+ allows default/static)
Variables	Can have instance variables	Only constants (public static final)
Inheritance	Supports single inheritance	Supports multiple inheritance
Constructor	Yes	No

Why Use Abstraction?

• Hide complexity
• Improve modularity
• Enhance code readability
• Encourage loose coupling

Real-World Analogy

Using an ATM:
• You press buttons (interface)
• Internally, it accesses your account, verifies PIN, updates the database (implementation)

You don't need to know how all of that works — that’s abstraction!

---