Class

1. What is a Class?

A class is a blueprint that defines the properties (variables) and behaviours (methods) that its objects will have. It doesn't hold real data by itself — it just describes the structure that objects created from it will follow.

2. Why is it used?

Classes let you model real-world things in code in an organized way. Instead of scattering related data and actions randomly, a class groups everything about one type of "thing" (like a Student or a Car) together in one place.

3. Real-Life Example

Think of a blueprint for a house. The blueprint itself is not a house you can live in — it just describes how each house built from it should look, with rooms, doors, and windows in specific places. A class is exactly this kind of blueprint for objects.

4. Syntax

java
class ClassName {
    // fields (variables)
    // methods
}

5. Example Program

java
class Student {
    String name;
    int rollNumber;
}

public class ClassDemo {
    public static void main(String[] args) {
        Student s = new Student();
        s.name = "Aditi";
        s.rollNumber = 12;
        System.out.println(s.name + " - " + s.rollNumber);
    }
}

Output:

Aditi - 12

6. Key Points to Remember

• A class by itself takes no memory for data — memory is used only when an object is created from it.
• A class can contain fields, methods, constructors, and more.
• One Java file can have multiple classes, but only one can be public.