Abstraction and abstract classes

1 Learn

Abstraction means showing what something does and hiding the details of how. You press a TV remote button without knowing the circuits.

An abstract class cannot be instantiated directly. It may contain abstract methods (no body) that subclasses must implement, as well as normal methods.

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2 See the Code

Java

abstract class Payment {
    abstract void pay(double amount);

    void receipt() {
        System.out.println("Receipt printed");
    }
}

class UpiPayment extends Payment {
    void pay(double amount) {
        System.out.println("Paid " + amount + " by UPI");
    }
}

public class Shop {
    public static void main(String[] args) {
        Payment p = new UpiPayment();
        p.pay(250);
        p.receipt();
    }
}

pay() is abstract — every concrete subclass must write it.
receipt() is a normal method shared by all payments.
new Payment() would be an error because Payment is abstract.

Output

Paid 250.0 by UPI
Receipt printed

3 Practice

Add a CardPayment class that extends Payment and prints Paid ... by Card.

Try it in your own Java setup or write it in the Practice Notebook.

4 Quick Check

1. Can you write new Payment() if Payment is abstract?
2. An abstract method has...

Step 5

Answer and check the Quick Check above to unlock this.

Day 20