Difference Between Object and Class in Kotlin

1. Introduction

In Kotlin, understanding the difference between class and object is crucial for proper object-oriented programming. A class in Kotlin is a blueprint for creating objects. It can contain properties, methods, and constructors. An object, on the other hand, is a singleton instance of a class. The object declaration in Kotlin combines class declaration and its single instance creation into one concise statement.

2. Key Points

1. Instances: A class can have multiple instances, an object is a single instance.

2. Declaration: Classes are declared using the class keyword, and objects are declared using the object keyword.

3. Initialization: Objects are initialized when they are first accessed, and classes are initialized when instantiated.

4. Use Case: Objects are used for singletons and utility functions, and classes are used for creating multiple objects with similar properties and behaviors.

3. Differences

Characteristic	Class	Object
Instances	Multiple instances	Single instance (Singleton)
Declaration	class keyword	object keyword
Initialization	When instantiated	When first accessed
Use Case	Creating multiple objects	Singletons, utility functions

4. Example

// Example of a Class
class MyClass {
    var name: String = "MyClass"
    fun showName() {
        println(name)
    }
}

// Example of an Object
object MyObject {
    var name: String = "MyObject"
    fun showName() {
        println(name)
    }
}

Output:

Class Output:
Creating an instance of MyClass and calling showName will print "MyClass"
Object Output:
Calling showName on MyObject will print "MyObject"

Explanation:

1. MyClass can be instantiated multiple times, each instance having its own name property.

2. MyObject is a single instance, and its name property is shared across the entire application.

5. When to use?

- Use class when you need to create multiple instances, each with their own state.

- Use object for singletons where only a single instance should exist, or for utility functions that do not require multiple instances.