Scala – Inheritance

In the previous post, we have learnt about method overloading. Now, we will see what is Inheritance in scala.

Inheritance is used for reusability of the code. When a class wants to use/reimplement code from another class, then that class has to use keyword extends to inherit properties from another class. The class which is extended , is called the Parent class or Super class. The class which extends another class, is called the subclass or child class.

Syntax:

class Birthday extends GreetingCards {
//Birthday - Subclass or child class
//GreetingCards - Parent class
}

Let’s understand this with an example.

Parent Class:

class Bank {
    var InterestRate: Int = 8
  def bankInterest(): Unit ={
    println("This bank's interest rate is : " +InterestRate)
  }
}

Child class extends parent class.

class hdfcBank extends Bank{
  var hdfcInterestRate = 7.5
  bankInterest()    //calling method of parent class
  println("Hdfc bank interest rate is : "+ hdfcInterestRate)
}

Now, create an object of child class and execute the program. Child class is directly calling parent class method.

object OurBank {
  def main(args: Array[String]): Unit = {
    new hdfcBank
  }
}

Output:
Global bank's interest rate is : 8
Hdfc bank interest rate is : 7.5

Types of Inheritance in Scala

Scala supports various types of inheritance including single, multilevel, multiple, hierarchal and hybrid.A point to be noted here is that , a class can only use single, multilevel and hierarchal inheritance. Multiple and hybrid will be used by Traits, which we will study in coming chapters.

Multilevel Inheritance in scala:

Let’s understand with an example where class C extends class B and class B extends class A.

package main.com.testingpool

class A {
  println("A")

}

class B extends A{
  println("B")

}
class C extends B{
  println("C")

}

object ABC{
  def main(args: Array[String]): Unit = {
    new C
  }
}

Output:
A
B
C

Example- Hierarchical Inheritance

In this example, class B and C both extends class A.

package main.com.testingpool

class A {
  println("A")

}

class B extends A{
  println("B")

}
class C extends A{
  println("C")

}

object ABC{
  def main(args: Array[String]): Unit = {
    new B()
    println("****")
    new C()
  }
}

Output:
A
B
****
A
C