Abstraction shows only essential features, hiding implementation details. Reduces complexity and improves security.

Definition List

• Abstraction: Hiding implementation details, showing only essential functionality.
• Abstract Class: Declared with abstract keyword. Cannot be instantiated.
• Abstract Method: Method with no body. Must be implemented by subclasses.
• Implementation: Actual code defining how a method works.

Abstract Method Syntax

abstract void draw();

Abstract Class Syntax

abstract class Shape {
    abstract void draw();
}

Rules of Abstract Classes

• Cannot be instantiated.
• Can contain abstract and non-abstract methods.
• Subclass must implement all abstract methods.
• Must have at least one abstract method.

Example 01: Abstract Class in Java

abstract class Shape {
    abstract void draw();

    void message() {
        System.out.println("Message From Shape");
    }
}

class rectangleShape extends Shape {
    @Override
    void draw() {
        System.out.println("Draw Rectangle Using Length & Breadth..");
    }
}

public class abstractDemo {
    public static void main(String args[]) {
        rectangleShape o = new rectangleShape();
        o.draw();
        o.message();
    }
}

Output

Draw Rectangle Using Length & Breadth..
Message From Shape

Key Points

• Abstract methods have no body.
• Must be declared inside abstract classes.
• Abstract classes cannot be instantiated.
• Subclasses must implement abstract methods.
• Abstraction works via abstract classes and interfaces.

FAQ

1. What is abstraction in Java?

Hiding implementation details and showing only essential functionality.

2. Can we instantiate an abstract class?

No. Create objects using the subclass instead.

3. Abstract method vs normal method?

Abstract has no body. Normal method has full implementation.