(11) Traits

About

:octocat: GitHub: All of the example code: repo (link)

:page_facing_up: blog link: https://purrgramming.life/cs/programming/fp/ :star:

Motivation

In Java, as well as in Scala, a class can only have one superclass.

But what if a class has several natural supertypes to which it conforms or from which it wants to inherit code? Here, you could use traits.

Classes, objects and traits can inherit from at most one class but many arbitrary traits.

Scala Trait vs Java Interface

Traits resemble interfaces in Java but are more powerful because they have parameters and contain fields and concrete methods.

Similarly to Java, in Scala, it is possible to

• have only one superclass
• can extend multiple traits (interfaces in Java)

Usage

Traits are similar to interfaces in Java and are created using trait keywords.

But what if a class has several natural supertypes to which it conforms or
from which it wants to inherit code?

Here, you could use traits.

A trait is declared like an abstract class, just with a trait instead of
abstract class

// Creating a super class  
abstract class Shapes {  
  def draw() = println("Draw the shape")  

  // Overload  
  def draw(id: Int) = println(s"Draw the shape (Id: $id)")  
}  

trait MathShape {  
  def size: Int  
}  

// Creating a subclass  
class Rectangle extends Shapes {  
  def size = println("length (L) * width (W) ")  
}  

// Creating a subclass  
class Circle extends Shapes {  
  // Overriding  
  override def draw() = println("Draw the Circle")  

  // Override, Overload  
  override def draw(id: Int) = println(s"Draw the Circle (Id: $id)")  

  def size = println("pi * radius^2 ")  
}  

val rectangle = new Rectangle  
rectangle.draw()  
rectangle.draw(0)  
rectangle.size  

val circle = new Circle  
circle.draw()  
circle.draw(1)  
circle.size

Abstract Class vs Trait

image source: https://drek4537l1klr.cloudfront.net/sfregola/v-2/Figures/11_02.png