Classes in Scala

Scala Tutorial

2 min readDec 9, 2018

Classes in Scala are declared using a syntax which is close to Java’s syntax with one important difference is that classes in Scala can have parameters.

If no constructor is defined, a class has a default constructor which takes no arguments.

The below class, SimpleClass has a primary constructor which is in the class signature (name: String, age: Int).

/**
  * Classes in Scala are declared using a syntax which is close to
  * Java's syntax with one important difference is that classes in
  * Scala can have parameters.
  *
  * This SimpleClass class takes two arguments: name and age.
  * These arguments must be passed when creating an instance of 
  * class SimpleClass as follows: new SimpleClass("John", 30).
  */
class SimpleClass (name: String, age: Int) {
  def showName() = name
  def showAge() = age
}

The SimpleClass class takes two arguments and these arguments must be passed when creating an instance as follows:

new SimpleClass("John", 30)

A class can inherit from multiple traits but only one abstract class.

Methods without arguments

We don’t need to put an empty pair of parenthesis after method name — removing empty pair of parenthesis is perfectly doable in Scala as follows:

def showName = name
def showAge = age

Supper-class

All classes in Scala inherit from a super-class.

When no super-class is specified, scala.AnyRef is implicitly used.

Classes can only have one super-class but many mixins (using the keywords extends and withrespectively).

What can’t be done with Classes?

Public access modifier is not allowed — Scala class is public by default.

Differences and Similarities with Java

Differences

Classes in Scala cannot have static members.
“public” access modifier is not allowed.
Classes are public by default — Java’s default modifier i.e. “protected” has visibility only within its own package.
Classes can have parameters.
Can have multiple public classes in a Scala source file — Unlike Scala, Java source file can have only one public class.
There is no need to match the source filename with the public class name.
We must initialize with some value to variables because we cannot define a variable with no value!

Similarities

Like Java, classes can be instantiated using the new construct.
There can be many “instances” (or “objects”) of the same class.

Scala Exercises: https://github.com/SenthilNayagan/scala-tutorial