What is the difference between a class and an object?

The blueprint idea

Think of a class like the architectural plan for a house. The plan lists the number of rooms and the layout, but you cannot live in a plan. An object is the real house built from that plan. From one plan you can build many houses, and from one class you can create many objects.

class Car {          // class: the blueprint
public:
    string model;
    void drive() { cout << "driving"; }
};

Car car1;               // object 1
Car car2;               // object 2
car1.model = "Tesla";
car2.model = "Honda";

class Car {          // class: the blueprint
    String model;
    void drive() { System.out.println("driving"); }
}

Car car1 = new Car();   // object 1
Car car2 = new Car();   // object 2
car1.model = "Tesla";
car2.model = "Honda";

class Car:              # class: the blueprint
    def drive(self):
        print("driving")

car1 = Car()            # object 1
car2 = Car()            # object 2
car1.model = "Tesla"
car2.model = "Honda"

Here Car is the class. The variables car1 and car2 are two separate objects. Each object has its own copy of the data, so changing car1 does not affect car2.

Quick comparison

• A class is a definition, an object is an instance of that definition.
• A class does not take memory for data on its own, an object takes memory when created.
• You write a class once, you can create many objects from it.
• The keyword new is used to create an object from a class in most languages.