LESSON 288 OF 677 · FUNCTIONS & CLASSES

Class Fields in Scala

Lesson

TL ; DR:

A field is a variable that lives inside a class. Each object of that class has its own copy.
Declare a field with var, a name, a type and an initial value. Fields are public unless you mark them private, so other code can read and write them:
```
class Dog {
    var name: String = ""
    var age: Int = 0
}
```
Access a field on an object with the dot operator: dog.name = "Rex"

Full lesson:

Right now your Dog class is just an empty shell — every Dog object you create is identical to every other one. We need a way to attach data to each object.

That's what fields are for. A field is a variable that belongs to a class — and each object created from that class gets its own copy of every field.

Declaring fields

class Dog {
    var name: String = ""
    var age: Int = 0
}

Scala has no public keyword: a member is public by default, meaning any code can read and write it. You'll see private later for fields that should only be touched by the class itself.
var name: String = "" is just a variable declaration — same syntax you'd use anywhere else. var lets the field be reassigned later.

Reading and writing fields

val dog = Dog()
dog.name = "Rex"        // write
dog.age = 4
println(dog.name)   // read → prints "Rex"

Each object has its own slot for every field, so two dogs can have different names without interfering.

Default values

Scala does not fill in a field for you: every field needs an initial value, and a var field with none is a compile error. Pick a sensible placeholder:

0 for numbers
false for Boolean
"" for a String

Your task

Update the Dog class to have two fields: name (a String) and age (an Int). Then in mainFunction, set them on the dog object so the pre-filled println prints:

Rex is 4 years old

STEP 1 OF 2

Guided

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