4.2.1. What is a Class?

A class is a blueprint or template for creating objects. It defines:

• Properties (also called fields or attributes)
• Behaviors (also called methods or functions)

A class can be thought of as a blueprint that defines what an object can do and what information it can hold. The properties of a class are the data variables that describe the object, while the behaviors represent the functions or methods that perform tasks on the object's data.

Imagine you're designing a car. The class of the car would include details like the color of the car (property), the make and model (attributes), and actions like accelerating, braking, or honking the horn (methods). Just as a blueprint provides the structure to build individual cars, a class provides the structure to create specific objects in programming.

📌 Syntax of a Class:

class ClassName {
// variables
// methods
}

The syntax for defining a class includes the keyword 'class' followed by the name of the class (which can be any valid identifier). Within the curly braces, you can define variables (attributes) and methods. This structure supports both clarity and functionality, allowing for an organized way to encapsulate related data and behaviors.

Continuing with the car analogy, if you were to write this in a programming language, it would look like a structured outline. Think of it as a recipe: the class defines all the ingredients (variables) you need and the steps (methods) to create your dish. Just like every recipe has its own format, every class has its own syntax to follow.

✅ What is an Object? An object is a real-world entity based on a class. It holds actual values.

An object is an instance of a class. While the class serves as a blueprint, an object is a concrete element created based on that blueprint. This means that when you create an object, you can assign specific values to the properties defined in the class, and then use the methods of that class to manipulate those values.

Think of the class as a blueprint for a house (like the car analogy), while each actual house built using that blueprint represents an object. You can have several houses (objects) built from the same design (class) but each can have different paint colors, gardens, or furnishings—these variations reflect the unique values assigned to each object.

🧪 Example:

class Student {
int id;
String name;
void display() {
System.out.println("ID: " + id);
System.out.println("Name: " + name);
}
}

public class Main {
public static void main(String[] args) {
Student s1 = new Student(); // Creating object
s1.id = 101;
s1.name = "Aman";
s1.display(); // Calling method
}
}

💬 Output: ID: 101 Name: Aman

In this example, a class named 'Student' is defined, which contains properties (id and name) and a method (display). The main program creates an object 's1' of the class 'Student', assigns values to the properties, and then calls the display method to show the values. This illustrates how classes and objects work together in programming.

Using the student example, think of 'Student' as the class that defines what students are. Each student you know (like Aman) is an object of that class. When Aman introduces himself, he shares his ID and name, just like the object displays its properties using the method in the class definition.

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