Difference Scala Class Declaration - scala

Question

I want to ask what's the difference between these two Class Declarations below.
class Person(name: String, age: Int)
or
class Person() {
var name: String = ""
var age: Int = 0
}

Answer 1

class Person(name: String, age: Int)
name and age are constructor parameters. As such they are:
required - in order to create a Person instance
immutable - the values cannot be changed
private - (by default) and cannot be accessed via a class instance
class Person() {
var name: String = ""
var age: Int = 0
}
name and age are class data members. They are:
not specified during construction - but are given the same default values for every Person instance
mutable - because they are var variables
public - (by default) and can be accessed and modified via a class instance
So, what's the difference? Almost everything.

Answer 2

The first declaration uses name and age as constructor arguments, but they do not become members of the class, that is you can't write person.name.
For a beginner, the second line can be considered a more complicated way to write class Person(var name: String = " ", var age: Int = 0). It actually doesn't translate to exactly the same thing: your version creates a class that has a single constructor argument and two public variables, while mine has a constructor with 2 arguments that have default values. Unless you have a good reason to declare it your way, it's usually better to write:
val person = new Person("Andrew", 11)
than
val person = new Person()
person.name = "Andrew"
person.age = 11
which is what your second version would force you to do.
Note that in Scala, you will mostly be using values (constants) and not variables, so you'd actually typically use class Person(val name: String = " ", val age: Int = 0). For simple data types like this, people typically use a case class:
case class Person(name: String, age: Int)
In this case, both argument are considered public and immutable. The only way to modify a person's name is to create another instance of Person with the new name:
val andrew = Person("Andrew", 11)
val will = andrew.copy(name="Will") # Will is also 11
Case classes will automatically give you proper equals and hashCode implementation, as well as the copy method I used above. You can easily find more infos about them on the internet.