The 4 OOP Pillars: Encapsulation, Inheritance, Polymorphism, Abstraction

private getters/setters, extends, super, @Override, abstract classes, and interfaces

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Object-Oriented Programming in Java is anchored on four fundamental pillars that promote modularity, reuse, and maintainability.

The 4 Pillars in Detail

1Encapsulation: Keeping fields private and exposing access via public getters/setters with validation.

2Inheritance: Subclasses inherit state and behavior from a superclass using extends.

3Polymorphism: Objects can be treated as instances of their parent type, invoking overridden methods dynamically at runtime (Dynamic Method Dispatch).

4Abstraction: Hiding internal implementation details using abstract class and interface.

Polymorphism and Interfaces in Action

Try It Yourself »

interface PaymentGateway {
    void processPayment(double amount);
}

class StripeGateway implements PaymentGateway {
    @Override
    public void processPayment(double amount) {
        System.out.println("Processing $" + amount + " via Stripe API.");
    }
}

class PayPalGateway implements PaymentGateway {
    @Override
    public void processPayment(double amount) {
        System.out.println("Processing $" + amount + " via PayPal Wallet.");
    }
}

public class Checkout {
    public static void executeOrder(PaymentGateway gateway, double total) {
        gateway.processPayment(total); // Polymorphic invocation!
    }
}

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Test Yourself With Exercise

+15 XP

Which keyword in Java allows a class to implement a contract defined by an interface?

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