Objects and Classes

🔍 What is a Class?#

In Java, a class is a user-defined data type that acts as a blueprint for creating objects. It defines:

• State (via fields/variables)
• Behavior (via methods/functions)

It encapsulates data for the object and methods to operate on that data.

🧱 What is an Object?#

An object is a runtime instance of a class. It represents an actual entity in the real world with:

• Actual values (unlike the abstract nature of a class)
• Ability to invoke methods defined in the class

✅ Example: Defining and Using a Class in Java#

We’ll model a real-world entity: Car

🔧 Car.java – Blueprint (Class)#

public class Car {
    // Fields (attributes)
    String color;
    int speed;

    // Method (behavior)
    void drive() {
        System.out.println("The " + color + " car is driving at " + speed + " km/h.");
    }
}

🚀 Main.java – Creating and Using Objects#

public class Main {
    public static void main(String[] args) {
        // Creating first object
        Car car1 = new Car();
        car1.color = "Red";
        car1.speed = 60;
        car1.drive();  // Output: The Red car is driving at 60 km/h.

        // Creating second object
        Car car2 = new Car();
        car2.color = "Blue";
        car2.speed = 90;
        car2.drive();  // Output: The Blue car is driving at 90 km/h.
    }
}

🧠 Key Concepts Explained#

This approach adheres to Object-Oriented Programming (OOP) principles such as encapsulation and modularity.

🎯 Why This Matters#

• Java is inherently object-oriented. Understanding classes and objects is foundational for mastering frameworks like Spring, Hibernate, and even for working with design patterns and architecture.
• In real-world projects, everything revolves around modeling real or abstract entities using classes.

📝 Homework for Students#

Task:#

1. Create a Student class with:

   • name (String)
   • age (int)
   • A method introduce() that prints:
     "Hi, my name is Alex and I am 21 years old."

2. In your main method:

   • Create two Student objects with different data
   • Call the introduce() method on both

✅ Let me know if you’d like to proceed to:

• Constructors in Java, or
• Methods and Parameters (deeper dive)?