class

Learn to define classes with class.

class: define a new type

A class defines a new type; inside it, data and behaviour live together. In its simplest form a class can have an empty body.

class Person

val p = Person()

This declaration creates a new type called Person. The call Person() creates an instance of this type. Class names usually start with an uppercase letter; this is a common convention.

Creating instances

To create an instance of a class you call the class name with parentheses. An instance is a concrete object of that class.

val p = Person()
val q = Person()
// p and q are different instances

Each call creates a new object; two instances are independent. You assign the instance to a val variable to reuse it. In later lessons you will add properties and behaviour to the instance.

Exercise Define a class and create an instance

Define an empty-bodied class called Person. In main create an instance and print "Person ready" with println.

Show example solution

class Person

fun main() {
    val p = Person()
    println("Person ready")
}

Test yourself

What does class Person define?
- A function
- A template type
- A constant
- An interface
Show answer

A template type — class defines a new type as a template.
Fill in the blank: declare a class
```
class ____ { }
```
Show answer
```
class Person { }
```
Match concept to meaning

class

Template
Person()

Instance
Person

Type name
val p

Variable

Next lesson: Constructor

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