1. Introduction to Abstraction

1.1 What is Abstraction

Abstraction means hiding internal details and showing only essential functionality to the user.

1.2 Why Use Abstraction

Reduces complexity
Improves code readability
Enhances security

1.3 Real-World Example

ATM machine:

User → withdraw money
Hidden → internal processing

1.4 Abstraction vs Encapsulation

Abstraction → hides implementation
Encapsulation → hides data

1.5 Ways to Achieve Abstraction

Abstract classes
Interfaces

2. Abstract Classes

2.1 Definition

An abstract class is a class that cannot be instantiated and may contain abstract methods.

2.2 Syntax

abstract class Vehicle {
    abstract void start();
}

2.3 Features

Can have abstract and non-abstract methods
Can have constructors
Cannot create objects directly

2.4 Example

abstract class Animal {
    abstract void sound();    void sleep() {
        System.out.println("Sleeping");
    }
}

2.5 When to Use

When classes share common behavior
When partial abstraction is needed

3. Abstract Methods

3.1 Definition

A method declared without implementation.

3.2 Syntax

abstract void display();

3.3 Rules

Must be inside abstract class
Must be implemented in subclass

3.4 Example

class Dog extends Animal {
    void sound() {
        System.out.println("Dog barks");
    }
}

4. Interfaces

4.1 Definition

An interface is a blueprint of a class that contains abstract methods.

4.2 Syntax

interface Animal {
    void sound();
}

4.3 Features

All methods are abstract by default (basic concept)
Cannot create objects
Supports multiple inheritance

4.4 Example

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

4.5 Interface vs Abstract Class

Feature	Abstract Class	Interface
Methods	Can have both	Mostly abstract
Inheritance	Single	Multiple

5. Implementing Interfaces

5.1 implements Keyword

Used to implement an interface.

5.2 Example

interface Vehicle {
    void start();
}class Car implements Vehicle {
    public void start() {
        System.out.println("Car starts");
    }
}

5.3 Key Points

Must override all methods
Use public access

6. Multiple Interface Implementation

6.1 Definition

A class can implement more than one interface.

6.2 Example

interface A {
    void show();
}interface B {
    void display();
}class Test implements A, B {
    public void show() {
        System.out.println("Show method");
    }    public void display() {
        System.out.println("Display method");
    }
}

6.3 Advantages

Achieves multiple inheritance
Improves flexibility

Conclusion

Abstraction is a powerful concept that helps simplify complex systems by hiding unnecessary details. By using abstract classes and interfaces, developers can build flexible and scalable Java applications. Understanding abstraction is essential for mastering Object-Oriented Programming and real-world software design.

Abstraction