What is the difference between a class and an object
💡 Concept: Class vs Object in Java
A class is a blueprint or template for creating objects, while an object is an instance of a class containing actual data and behavior.
📘 Quick Intro
Classes define properties and methods, and objects are concrete entities created based on classes to hold state and provide functionality.
🧠 Analogy
Think of a class as a blueprint for a car design, and the object as an actual car built from that blueprint, ready to be driven.
🔧 Technical Explanation
- Classes define the data members (fields) and behaviors (methods).
- Objects are runtime instances occupying memory.
- Multiple objects can be created from a single class.
- Classes provide abstraction, objects provide implementation.
- Objects can interact with other objects via methods.
🎯 Use Cases
- ✅ Use classes to model real-world entities and abstract data.
- ✅ Create objects to work with actual data instances in programs.
- ✅ Use objects for state management and behavior execution.
💻 Code Example: Class and Object
public class Car {
String color;
int speed;
public void accelerate() {
speed += 10;
System.out.println("Accelerating. Speed: " + speed);
}
}
public class Main {
public static void main(String[] args) {
Car myCar = new Car();
myCar.color = "Red";
myCar.accelerate();
}
}
❓ Interview Q&A
Q1: What is a class?
A: A blueprint to create objects.
Q2: What is an object?
A: An instance of a class.
Q3: Can multiple objects be created from one class?
A: Yes.
Q4: Does a class hold actual data?
A: No, objects hold data.
Q5: What is encapsulation?
A: Bundling data and methods in a class.
Q6: Is a class an object?
A: No, but objects are instances of classes.
Q7: Can objects interact with each other?
A: Yes, via method calls.
Q8: What does instantiation mean?
A: Creating an object from a class.
Q9: Can a class have methods?
A: Yes.
Q10: Are classes reusable?
A: Yes, they promote code reuse.
📝 MCQs
Q1. What is a class?
- An instance
- A blueprint to create objects
- A variable
- A method
Q2. What is an object?
- A class
- An instance of a class
- A method
- A variable
Q3. Can multiple objects be created from one class?
- No
- Yes
- Maybe
- Only one
Q4. Does a class hold actual data?
- Yes
- No, objects hold data
- Sometimes
- Depends on class
Q5. What is encapsulation?
- Separating code
- Hiding methods
- Bundling data and methods in a class
- Exposing all data
Q6. Is a class an object?
- Yes
- No, but objects are instances of classes
- Sometimes
- Never
Q7. Can objects interact with each other?
- No
- Yes
- Sometimes
- Never
Q8. What does instantiation mean?
- Deleting an object
- Creating an object from a class
- Modifying a class
- Compiling code
Q9. Can a class have methods?
- No
- Yes
- Only abstract
- Only static
Q10. Are classes reusable?
- No
- Yes
- Sometimes
- Rarely
💡 Bonus Insight
Classes and objects form the foundation of OOP in Java, enabling modular, reusable, and maintainable code.
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