. What is a Class?

A Class is a “Blueprint” or a “Template.” It is a logical entity that defines what an object will look like and how it will behave. It doesn’t exist in the physical world and doesn’t take up any memory space; it is just a set of instructions.

  • It contains: Variables (to store data) and Methods (to perform actions).

  • Analogy: A class is like the architect’s drawing of a house. You cannot live in the drawing, but it tells you exactly where the walls and doors go.

2. What is an Object?

An Object is a “Physical Reality.” It is an instance of a class. When you create an object, Java allocates memory for it in the “Heap” memory.

  • It has: A State (data stored in variables) and Behavior (actions it can do).

  • Analogy: If the blueprint is the Class, then the actual house you build is the Object. You can build 100 different houses (Objects) from just one blueprint (Class).

3. Real-Life Examples

To make this clear for your exams and projects, use these standard examples:

Real-Life CategoryClass (The Template)Objects (The Instances)
AutomobilesCarYour neighbor’s Toyota, your friend’s Honda, a Tesla.
EducationStudentAli (Roll No 101), Sara (Roll No 102).
AnimalsDogA German Shepherd named “Max,” a Poodle named “Bella.”
BankingBankAccountYour Savings Account, a Company’s Current Account.

4. How to write them in Java?

Here is a simple university-level example. We define a class Mobile and then create objects from it.

The Class (Blueprint)

Java

 
class Mobile {
    // Attributes (State)
    String brand;
    int ram;

    // Method (Behavior)
    void makeCall() {
        System.out.println("Calling from " + brand);
    }
}

The Objects (Instances)

Java

 
public class Main {
    public static void main(String[] args) {
        // Creating Object 1
        Mobile phone1 = new Mobile();
        phone1.brand = "Samsung";
        phone1.ram = 8;

        // Creating Object 2
        Mobile phone2 = new Mobile();
        phone2.brand = "iPhone";
        phone2.ram = 6;

        phone1.makeCall(); // Output: Calling from Samsung
        phone2.makeCall(); // Output: Calling from iPhone
    }
}

5. Key Differences for Students

  • Memory: A Class takes no memory. An Object takes memory as soon as you use the new keyword.

  • Definition: A Class is defined only once. You can create infinite objects from it.

  • Manipulation: You cannot change a Class while the program is running, but you can change an Object’s data (like changing a car’s color).

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