Extending a Class in Scala

Extending a class in Scala user can design an inherited class. To extend a class in Scala we use extends keyword. there are two restrictions to extend a class in Scala :

• To override method in scala override keyword is required.
• Only the primary constructor can pass parameters to the base constructor.

Syntax:

class derived_class_name extends base_class_name
{
    // Methods and fields
}

Example:

// Scala program of extending a class

// Base class
class Geeks1
{
    var Name: String = "chaitanyashah"
}

// Derived class
// Using extends keyword
class Geeks2 extends Geeks1
{
    var Article_no: Int = 30

    // Method
    def details()
    {
        println("Author name: " + Name);
        println("Total numbers of articles: " + Article_no);
    }
}

// Creating object
object GFG
{

    // Driver code
    def main(args: Array[String])
    {

        // Creating object of derived class
        val ob = new Geeks2();
        ob.details();
    }
}

Output:

Author name: chaitanyashah
Total numbers of articles: 30

In the above example Geeks1 is the base class and Geeks2 is the derived class which is derived from Geeks1 using extends keyword. In the main method when we create the object of Geeks2 class, a copy of all the methods and fields of the base class acquires memory in this object. That is why by using the object of the derived class we can also access the members of the base class.

Example:

// Scala program of extending a class

// Base class
class Parent
{
    var Name1: String = "geek1"
    var Name2: String = "geek2"
}

// Derived from the parent class
class Child1 extends Parent
{
    var Age: Int = 32
    def details1()
    {
        println(" Name: " + Name1)
        println(" Age: "  + Age)
    }
}

// Derived from Parent class
class Child2 extends Parent
{
    var Height: Int = 164

    // Method
    def details2()
    {
        println(" Name: " + Name2)
        println(" Height: " + Height)
    }
}

// Creating object
object GFG
{

    // Driver code
    def main(args: Array[String])
    {

        // Creating objects of both derived classes
        val ob1 = new Child1();
        val ob2 = new Child2();
        ob1.details1();
        ob2.details2();
    }
}

Output:

Name: geek1
Age: 32
Name: geek2
Height: 164

In the above example Parent is the base class Child1 and Child2 are the derived class which is derived from Parent using extends keyword. In the main method when we create the objects of Child1 and Child2 class a copy of all the methods and fields of the base class acquires memory in this object.
Example:

// Scala program of extending a class

// Base class
class Bicycle (val gearVal:Int, val speedVal: Int)
{
    // the Bicycle class has two fields
   var gear: Int = gearVal
   var speed: Int = speedVal

   // the Bicycle class has two methods
   def applyBreak(decrement: Int)
   {
       gear = gear - decrement
       println("new gear value: " + gear);
   }
   def speedUp(increment: Int)
   {
       speed = speed + increment;
       println("new speed value: " + speed);
   }
}

// Derived class
class MountainBike(override val gearVal: Int,
                    override val speedVal: Int,
                    val startHeightVal : Int)
                    extends Bicycle(gearVal, speedVal)
{
    // the MountainBike subclass adds one more field
   var startHeight: Int = startHeightVal

   // the MountainBike subclass adds one more method
   def addHeight(newVal: Int)
   {
       startHeight = startHeight + newVal
       println("new startHeight : " + startHeight);
   }
}

// Creating object
object GFG
{
    // Main method
    def main(args: Array[String])
    {
        val bike = new MountainBike(10, 20, 15);

        bike.addHeight(10);
        bike.speedUp(5);
        bike.applyBreak(5);
    }
}

Output:

new startHeight : 25
new speed value: 25
new gear value: 5

In above program, when an object of MountainBike class is created, a copy of the all methods and fields of the superclass acquire memory in this object.