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Scala | Final
  • Last Updated : 14 Mar, 2019

In Scala, Final is a keyword and used to impose restriction on super class or parent class though various ways. We can use final keyword along with variables, methods and classes.
Following are the ways of using final keyword in Scala

  1. Scala Final Variable:
    Scale final variable initialized only once while declared and used as constant throughout the program. In below example, variable area is final which is declared as final and also initialized while declare in superclass shapes. if we want to access or modify the variable area from derived class Rectangle then it is not possible because the restriction on variable area is added by keyword final.

    Scala final variable initialized by following ways:

    • While declaring
    • In static block
    • In Constructor




    // Scala program of using final variable
    class Shapes
        // define final variable
        final val area:Int = 60
    class Rectangle extends Shapes
        override val area:Int = 100
        def display()
        
            println(area) 
        
      
    // Creating object
    object GFG
        // Main method
        def main(args:Array[String])
        
            var b = new Rectangle() 
            b.display() 
        
    }

    Following error occurs while running above code

    Output :



     
    prog.scala:5: error: overriding value area in class Shapes of type Int;
     value area cannot override final member
    override val area:Int = 100
                 ^
    one error found
    

  2. Scala Final Methods:
    Final method CalArea in the parent class (Shapes) indicate that, method cannot override in a child class (Rectangle).




    // Scala program of using final method
    class Shapes
        val height:Int = 0
        val width :Int =0
          
        // Define final method
        final def CalArea(){ 
        }
    class Rectangle extends Shapes
        override def CalArea()
        
            val area:Int = height * width 
            println(area) 
        
      
    // Creating object
    object GFG
        // Main method
        def main(args:Array[String])
        
            var b = new Rectangle() 
            b.CalArea() 
        
    }

    Following error occurs while running above code

    Output :

    prog.scala:8: error: overriding method CalArea in class Shapes of type ()Unit;
     method CalArea cannot override final member
        override def CalArea(){
                         ^
    one error found
    

  3. Scala Final Classes
    If the class in Scala is final then it cannot inherit to derived class. Inheritance restriction will be added by final keyword. Here if class Shapes are final then its all members also final and cannot used in derived class.




    // Scala program of using final class
    final class Shapes
        // Final variables and functions
        val height:Int = 0
        val width :Int =0
        final def CalArea()
        
        }
    class Rectangle extends Shapes
        // Cannot inherit Shapes class 
         override def CalArea()
         
            val area:Int = height * width 
            println(area) 
        
      
    // Creating Object
    object GFG
        // Main method
        def main(args:Array[String])
        
            var b = new Rectangle() 
            b.CalArea() 
              
        
    }

    Following error occurs while running above code

    Output :

     
    prog.scala:4: error: illegal inheritance from final class Shapes
    class Rectangle extends Shapes{
                            ^
    one error found
    



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