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Calling A Super Class Constructor in Scala

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  • Last Updated : 28 Feb, 2022
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Prerequisite – Scala Constructors
In Scala, Constructors are used to initialize an object’s state and are executed at the time of object creation. There is a single primary constructor and all the other constructors must ultimately chain into it. When we define a subclass in Scala, we control the superclass constructor that is called by its primary constructor when we define the extends portion of the subclass declaration. 
 

  • With one constructor: An example of calling a super class constructor 
    Example: 
     

Scala




// Scala program to illustrate
// calling a super class constructor
 
// Primary constructor
class GFG (var message: String)
{
    println(message)
}
 
 
// Calling the super class constructor
class Subclass (message: String) extends GFG (message)
{
    def display()
    {
        println("Subclass constructor called")
    }
}
 
// Creating object
object Main
{
    // Main method
    def main(args: Array[String])
    {
         
        // Creating object of Subclass
        var obj = new Subclass("Geeksforgeeks");
        obj.display();
    }
}

  •  
Output: 

Geeksforgeeks
Subclass constructor called

 

  • In the above example, the subclass is defined to call the primary constructor of the GFG class, which is a single argument constructor that takes message as its parameter. When defining a subclass in Scala, one controls the Superclass constructor that’s called by the Subclass’s primary constructor when defining the extends segment of the Subclass declaration.
  • With multiple constructors : In a case with the Superclass having multiple constructors, any of those constructors can be called using the primary constructor of the Subclass. For Example, in the following code, the double argument constructor of the Superclass is called by the primary constructor of the Subclass using the extends clause by defining the specific constructor.
    Example: 
     

Scala




// Scala program to illustrate
// calling a specific super class constructor
 
// Primary constructor (1)
class GFG (var message: String, var num: Int)
{
     
    println(message+num)
     
    // Auxiliary constructor (2)
    def this (message: String)
    {
        this(message, 0)
         
    }
     
}
 
// Calling the super class constructor with 2 arguments
class Subclass (message: String) extends GFG (message, 3000)
{
    def display()
    {
        println("Subclass constructor called")
    }
}
 
// Creating object
object GFG
{
    // Main method
    def main(args: Array[String])
    {
         
        // Creating object of Subclass
        var obj = new Subclass("Article count ");
        obj.display();
    }
}

  •  
Output: 

Article count 3000
Subclass constructor called

 

  •  
  • We can call the single argument constructor here, By default another argument value will be 0. 
    Example: 
     

Scala




// Scala program to illustrate
// calling a specific super class constructor
 
// Primary constructor (1)
class GFG (var message: String, var num: Int)
{
     
    println(message + num)
     
    // Auxiliary constructor (2)
    def this (message: String)
    {
        this(message, 0)
         
    }
     
}
 
 
// Calling the superclass constructor with 1 arguments
class Subclass (message: String) extends GFG (message)
{
    def display()
    {
        println("Subclass constructor called")
    }
}
 
// Creating object
object GFG
{
    // Main method
    def main(args: Array[String])
    {
         
        // Creating object of Subclass
        var obj = new Subclass("Article Count ");
        obj.display();
    }
}

  •  
Output: 

Article Count 0
Subclass constructor called

 

 


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