What is the difference between a class and an object?
Theme: Programming Role: Software Engineer Function: Technology
Interview Question for Software Engineer: See sample answers, motivations & red flags for this common interview question. About Software Engineer: Develops and maintains software applications. This role falls within the Technology function of a firm. See other interview questions & further information for this role here
Sample Answer
Example response for question delving into Programming with the key points that need to be covered in an effective response. Customize this to your own experience with concrete examples and evidence
- Definition: A class is a blueprint or template for creating objects. It defines the properties and behaviors that an object of that class will have. An object, on the other hand, is an instance of a class. It is a concrete entity that can be created based on the class definition
- Relationship: A class is a general concept, while an object is a specific instance of that concept. Multiple objects can be created from a single class
- Usage: Classes are used to define the structure and behavior of objects. They encapsulate data and methods that operate on that data. Objects, on the other hand, are used to represent specific instances of a class and interact with other objects
- Creation: A class is created using a class declaration, which defines its properties and methods. An object is created by instantiating a class using the 'new' keyword
- Inheritance: Classes can inherit properties and methods from other classes, forming a hierarchical relationship. Objects do not inherit from other objects
- Memory: Classes are stored in memory as code, while objects are stored in memory as data
- Access: Classes can have access modifiers (e.g., public, private) to control the visibility of their members. Objects can access the public members of their class
- Static vs. Instance: Classes can have static members that belong to the class itself, while objects have instance members that belong to a specific object
- Examples: For example, a class 'Car' can define properties like 'color' and 'model', and methods like 'startEngine()' and 'accelerate()'. An object 'myCar' can be created from the 'Car' class with specific values for its properties
- Abstraction: Classes provide abstraction by hiding the internal implementation details and exposing only the necessary information through their public interface. Objects encapsulate data and behavior, providing a higher level of abstraction
- Dynamic Behavior: Classes define the behavior of objects, but objects can have dynamic behavior based on their state and the methods they invoke
- Relationship with OOP: Classes and objects are fundamental concepts in object-oriented programming (OOP). OOP promotes modular and reusable code by organizing it into classes and creating objects from those classes
- Encapsulation: Classes encapsulate data and methods, allowing for data hiding and providing a clear interface for interacting with objects. Objects encapsulate their state and behavior, ensuring data integrity and modularity
- Polymorphism: Classes can participate in polymorphism, where objects of different classes can be treated as objects of a common superclass. Polymorphism allows for code reuse and flexibility
- Memory Efficiency: Classes are memory-efficient as they are shared among multiple objects. Objects consume memory based on their specific data and state
- Design Patterns: Classes and objects are key components in various design patterns, such as Singleton, Factory, and Observer, which provide solutions to common software design problems
Underlying Motivations
What the Interviewer is trying to find out about you and your experiences through this question
- Knowledge of Object-Oriented Programming: Understanding the fundamental concepts of OOP
- Understanding of Software Development: Ability to differentiate between class and object in software development
- Problem-solving Skills: Capability to apply class and object concepts in real-world scenarios
- Communication Skills: Ability to explain technical concepts in a clear and concise manner
Potential Minefields
How to avoid some common minefields when answering this question in order to not raise any red flags
- Confusing class & object: Mixing up the definitions or using them interchangeably
- Lack of understanding of object-oriented programming: Inability to explain the basic concepts of classes and objects
- Inability to differentiate between class & instance: Not understanding that a class is a blueprint while an object is an instance of that class
- Not mentioning the relationship between class & object: Failing to explain that objects are created from classes and inherit their properties and behaviors