Scala Inheritance – Syntax, Example & Types of Inheritance in Scala

In our last Scala Tutorial, we discuss Scala Case Class. Now, we will discuss Scala inheritance with syntax and examples. Along with this, we will cover different types of inheritance in Scala Programming. At last, we will see examples of multilevel inheritance and Hierarchical Inheritance in Scala.

Scala Inheritance – Syntax, Example & Types of Inheritance in Scala

Scala Inheritance

When a class inherits from another, it means it extends another. We use the ‘extends’ keyword for this. This lets a class inherit members from the one it extends and lets us reuse code.
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The class that extends is the subclass, the child class, or the derived class. The other class is the superclass, the parent class, or the base class.

It is an IS-A relationship. You can also call it a generalization. A Student is a Person.

A syntax of Scala Inheritance

To carry out Scala inheritance, we use the keyword ‘extends’:

class Student extends Person(){
/*your code
*goes here
*/

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Scala Inheritance Example

Let’s take an example of Inheritance.

scala> class Person{
| var SSN:String="999-32-7869"
| }
defined class Person
scala> class Student extends Person{
| var enrolment_no:String="0812CS141028"
| println("SSN: "+SSN)
| println("Enrolment Number: "+enrolment_no)
| }
defined class Student
scala> new Student()
SSN: 999-32-7869
Enrolment Number: 0812CS141028
res0: Student = Student@42cfd794

In this example, we have two classes- Person and Student. We make Student extend Person. This means a Student is a Person.
Since Student extends Person, it inherits the attribute holding the social security number. In class Student, we print SSN and enrolment_no. Finally, we create an object of class Student.

Types of Inheritance in Scala

Scala supports five kinds of inheritance:

a. Single-level Inheritance in Scala

Scala Single-level inheritance is when one class inherits from a single other class.

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b. Multilevel Inheritance in Scala

When one class extends another, which in turn extends another, it is an instance of multilevel inheritance.

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c. Multiple Inheritance in Scala

When one class inherits from multiple base classes, it is a case of multiple inheritances.

d. Hierarchical Inheritance in Scala

When more than one class inherits from one base class, it is said to be hierarchical inheritance.

e. Hybrid Inheritance in Scala

Scala Hybrid inheritance is a combination of at least two kinds of inheritance.

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Multilevel Inheritance Example – 1

scala> class A{
| println("A")
| }
defined class A
scala> class B extends A{
| println("B")
| }
defined class B
scala> class C extends B{
| println("C")
| }
defined class C
scala> new C()
A
B
C
res1: C = C@347f8029

In this example, we observe that class C extends class B and class B extends A.

Example – 2

Take a look at this code:

object Multiple{
        def main(args: Array[String]):Unit={
           trait A{
                   var length:Int= _
                   def action={
                     length=length+5
                  }
             }
           trait B{
                   var height:Int = _
                   def action={
                     height = height + 1
                  }
             }
           class C extends A with B{
                   length=3;
                   height+=6;
                   override def action={
                            super[A].action
                            super[B].action
                   }
              }
                var c=new C
                c.action
                println(c.height)
                println(c.length)
             }
}

Here, we make use of traits to let class C inherit from traits A and B.

Example- Hierarchical Inheritance

scala> class A{
| println("A")
| }
defined class A
scala> class B extends A{
| println("B")
| }
defined class B
scala> class C extends A{
| println("C")
| }
defined class C
scala> new B()
A
B
res2: B = B@64c1a76e
scala> new C()
A
C
res3: C = C@193f5509

In this example, classes B and C inherit from class A.
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Conclusion

Hence, we studied what is Inheritance in Scala with example and syntax. In addition, we saw different types of inheritance. If you have a doubt, feel free to ask in the comment section.
Related Topic- Scala Closures with Examples 
For reference