Differences between Class and Object
Contents
Class (computer programming) and object (computer science)
In object-oriented programming (OOP), a class and an object are distinct entities that work together to define and implement software structures. A class functions as a blueprint or template, while an object represents a specific instance of that template created during program execution. This distinction is a fundamental concept in languages such as Java, C++, and Python.[1]
Class
A class is a logical construct. It defines the variables and methods that all objects of a certain type will possess. It does not occupy memory for data storage until it is instantiated. A class declaration specifies the structure and behavior of the type but does not contain actual data for specific cases. For example, a class named "Car" might define attributes like "color" and "model," and behaviors like "accelerate" or "brake."[2]
Object
An object is a physical entity that exists in a computer's memory. It is created from a class through a process called instantiation. Each object has its own identity, state, and behavior. While the class defines what data an object can hold, the object itself holds the specific values. If the "Car" class is used to create an object, that specific object might have "Red" as its color and "Sedan" as its model. Multiple objects can be created from a single class, each maintaining independent data values while sharing the same underlying structure defined by the class.[3]
Comparison table
| Feature | Class | Object |
|---|---|---|
| Definition | A blueprint or template for creating objects. | An instance of a class. |
| Existence | Logical entity; exists in the source code. | Physical entity; exists in memory (RAM). |
| Memory | Does not allocate memory for data upon definition. | Allocates memory when created. |
| Quantity | Defined once per type. | Can be created in any number from a single class. |
| Components | Contains methods and variable declarations. | Contains specific values for data fields. |
| Lifetime | Persists throughout the program execution. | Created and destroyed during runtime. |
| Example | The concept of a "Bank Account." | A specific person's bank account with a $500 balance. |
Relationship and instantiation
The relationship between a class and an object is one of type and instance. To use the functionality defined in a class, a programmer must instantiate the class using a keyword, such as `new` in Java or C#. This command triggers the computer to allocate memory and initialize the object's variables according to the class definition. Once the object is created, the program can access its methods and modify its data.[3]
In many programming environments, classes also support inheritance. This allows one class to derive its structure from another. However, an object always belongs to a specific class type, even if that class is a child of a broader parent class. The management of these objects, including their creation and eventual removal from memory (often through garbage collection), is a primary task of the software's runtime environment.[4]
References
- ↑ Booch, Grady (2007). Object-Oriented Analysis and Design with Applications. Addison-Wesley. pp. 71–75. ISBN 978-0-201-89551-3.
- ↑ Stroustrup, Bjarne (2013). The C++ Programming Language (4th ed.). Addison-Wesley. pp. 450–455. ISBN 978-0-321-56384-2.
- ↑ 3.0 3.1 "What Is an Object?". The Java Tutorials. Oracle Corporation. Retrieved February 19, 2026.
- ↑ Schildt, Herbert (2018). Java: The Complete Reference (11th ed.). McGraw-Hill Education. pp. 115–120. ISBN 978-1-260-44023-2.
