Class Vs. Object: What are the Differences?
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Overview
In this article, we explore the fundamental difference between class and object in the context of object-oriented programming. We begin by defining a class as a template or blueprint, encompassing data members and methods. Objects, on the other hand, are instances created from these blueprints, each having unique values but sharing common behaviors.
Difference Between Class and Object
| Class | Object |
|---|---|
| A class is a blueprint for declaring and creating objects. | An object is a class instance that allows programmers to use variables and methods from inside the class. |
| Memory is not allocated to classes. Classes have no physical existence. | When objects are created, memory is allocated to them in the heap memory. |
| You can declare a class only once. | A class can be used to create many objects. |
| Class is a logical entity. | An object is a physical entity. |
| We cannot manipulate class as it is not available in memory. | Objects can be manipulated. |
| Class is created using the class keyword like class Dog{} | Objects are created through new keyword like Dog d = new Dog();. We can also create an object using the newInstance() method, clone() method, fatory method and using deserialization. |
| Example: Mobile is a class. | If Mobile is the class then iphone, redmi, blackberry, samsung are its objects which have different properties and behaviours. |
| Classes can have attributes and methods defined. | Objects can have specific values assigned to their attributes. |
| Classes serve as blueprints for creating objects. | Objects represent specific instances created from a class. |
What is Class?
A class is a blueprint or template for creating objects. It defines the data members and methods that objects will have. Classes are a fundamental concept in object-oriented programming (OOP).
A class can be understood as a template or blueprint of attributes and functions, which contains some values, known as data members, and some set of rules, known as behaviors or methods.
Syntax
Syntax of a class in C++
- class: The keyword used to define a class.
- ClassName: The name of the class.
- { }: The curly braces enclose the class members, including data members and member functions.
- Data members: Variables declared within the class that represent the data associated with objects of that class.
- Member functions: Functions declared within the class that define the behavior of objects of that class.
- public: The access specifier that determines which members are accessible outside the class.
Syntax of a class in Python
- class: The keyword used to define a class.
- ClassName: The name of the class.
- ( ): The parentheses enclose the class arguments, which are used to initialize the class attributes.
- Data members: Variables declared within the class that represent the data associated with objects of that class.
- __init__(self): The constructor method, which is automatically called when an object of the class is created.
- def member_function(self): Class methods, which define the behavior of objects of that class.
- self: The reference to the current object within the class methods.
Examples
C++:
Python:
In C++, data members and methods are explicitly defined within the class, while in Python, the __init__ method initializes data members, and methods are defined conventionally within the class.
Why are Classes used to create Custom Objects?
Classes are used to create custom objects in programming because they provide a structured and modular way to define the blueprint or template for these objects. Here are several reasons why classes are employed for creating custom objects:
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Encapsulation:
- Definition: Bundling data (attributes) and methods (functions) that operate on the data within a single unit (class).
- Advantage: Encapsulation allows the hiding of implementation details, promoting a cleaner and more organized code structure.
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Abstraction:
- Definition: Representing essential features of an object while hiding unnecessary details.
- Advantage: Abstraction simplifies the complexity of the real-world entities, making it easier for developers to comprehend and use the objects.
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Reusability:
- Definition: Creating a class once and using it in multiple parts of a program.
- Advantage: Classes enable the creation of reusable code, reducing redundancy and promoting a more efficient development process.
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Modularity:
- Definition: Breaking down a program into smaller, manageable parts (modules or classes).
- Advantage: Modularity allows developers to work on different components independently, enhancing maintainability and collaboration.
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Inheritance:
- Definition: Creating a new class by inheriting properties and behaviors from an existing class.
- Advantage: Inheritance promotes code reuse, as the new class can leverage functionalities of the existing class, avoiding duplication.
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Polymorphism:
- Definition: Allowing objects of different classes to be treated as objects of a common base class.
- Advantage: Polymorphism enhances flexibility by enabling the use of a single interface for different object types, simplifying code implementation and maintenance.
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Customization:
- Definition: Tailoring objects to specific needs by defining custom data members and methods.
- Advantage: Customization allows developers to create objects that precisely match the requirements of their applications.
What is an Object?
A class contains the properties and behaviour of a set of objects, many objects can be formed using a class.
- Take the example of a dog as an object.
- There are different varieties of dogs which means different varieties of objects according to the dog class. For example, one dog has black color, another dog may have grey color, or white, etc.
- However, we can notice that most of the behaviours are the same like barking, wagging their tail, eating, sleeping, etc.
- Properties and behaviour of these objects can be the same but their values would be different.
Syntax to create an object:
C++
Python
Explanation of the syntax:
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class ClassName: This defines a class named ClassName.
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Data members: This section defines the data members of the class. Data members are variables that store data associated with objects of the class.
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public:: This is an access specifier that determines which members of the class are accessible outside the class. Public members can be accessed from outside the class.
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Member functions: This section defines the member functions of the class. Member functions are methods that define the behavior of objects of the class.
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objectName: This creates an object of the class named ClassName.
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objectName.memberFunction(): This calls the memberFunction() method on the objectName object.
Example
C++
Explanation:
- The code defines a simple class Person with attributes name and age, and a method displayInfo.
- In the main function, an object person1 of the Person class is created.
- Attributes of the object are set, and the displayInfo method is called to show information.
Python
Explanation:
- The code defines a simple class Person with a constructor (__init__) to initialize attributes and a method display_info.
- An object person1 of the Person class is created with initial values.
- The display_info method is called to print information about the person.
Key Difference Between Class and Object
The main difference between class and object is that a class is a blueprint or a template that defines the properties and behaviors of a specific type of object. It serves as a blueprint for creating objects. On the other hand, an object is an instance of a class. It is a specific entity created from the class, and it represents a real-world concept. In simpler terms, a class defines the structure and behavior, while an object is an actual representation of that structure in memory. Classes can be considered as the blueprint of a house, while objects are the actual houses built based on those blueprints.
Conclusion
- Class is a blueprint that defines some properties and behaviors. An object is an instance of a class that has those properties and behaviours attached.
- A class is not allocated memory when it is defined. An object is allocated memory when it is created.
- Class is a logical entity whereas objects are physical entities.
- A class is declared only once. On the other hand, we can create multiple objects of a class.
- We can create a class using the class keyword. Objects can be created in many ways such as using the new keyword, newInstance() method,clone() method, factory method, and deserialization.