Top Interview Questions: Abstract Class vs. Interface in Java

Real-Life Scenarios

When to Use Abstract Classes

Scenario: Consider a software application for managing different types of vehicles. You may have a base class Vehicle that provides common properties and methods for all vehicles, such as brand, model, and a method displayDetails(). However, each specific vehicle type, such as Car, Bike, and Truck, may have different behaviors, such as how they start or their specific fuel consumption.

Implementation:

abstract class Vehicle {
    String brand;
    String model;

Vehicle(String brand, String model) {
        this.brand = brand;
        this.model = model;
    }
    abstract void start(); // Abstract method
    void displayDetails() {
        System.out.println("Brand: " + brand + ", Model: " + model);
    }
}
class Car extends Vehicle {
    Car(String brand, String model) {
        super(brand, model);
    }
    @Override
    void start() {
        System.out.println("Car is starting.");
    }
}

When to Use Interfaces

Scenario: In a payment processing system, you may have different payment methods such as CreditCard, PayPal, and BankTransfer. Each payment method will implement a common interface PaymentMethod that requires the implementation of a method processPayment(). This allows different payment methods to be used interchangeably.