Question

Consider the following Scala code that uses classes, objects, inheritance and dynamic method binding abstract class A { def m) Int 1 val a Int = 2 class B extends A { val b: String "one" override def m() : Int = 3 def n(): Int 4 class C extends A { val x : Int 5 override def m() : Int = 6 val array an array of ten A objects array (5) val obj: A obj.m() = (a) Explain in terms of Scala concepts how the object-oriented features of the language interact to determine which method gets called by the method call obj.m()

Answer 1

Ans a) In Scala object oriented features deal with classes and objects. I would like to explain the concept in terms of above code in a clear way. Here in above code we have abstract base class and inherited sub classes. In Scala also we have single,multilevel,multiple and Hierarchical Inheritances supported. The Subclasses can have their own methods and variables declared and used, at the same time have acces to all the methods and variables in base class. Basically Reusability is achieved. This is how inheritance works in Scala. When object is created for a particular subclass in main then immediately all the instances of variables and methods in base class is loaded into memory. Thats how the inherited subclasses can acces all the variables and methods in base class.

In above code Class A is abstract class whose variables and methods are only accesible to its inherited class. Function m() is been overrided in inherited classes B and C. If object is created for either of the classes B and C and if function m() is called using created object in main then you would get the overriden function m() of that particular subclass for which the object is created. Here the abstract class A is instantiated which is violating the rule of scala which states that "Abstract classes cannot be instantiated in scala". So in above code the object is created for class A which gives you error. So with obj.m() no method is called.

Ans b)
Abstract class A mc) Istall a-2 Base class Inheritance & class B b= öne" mer: Int=3 h(): Ist = 4 class c x=5 m(): Int=6 Inherited classes

when object is created for any of inherited classes. The instances of all variables and methods of Base class o are loaded into Memory as below Memory clou A. mui Int=1 a=2 so that any of subclasses and c can access immediately when needed the wye of variables and methods in class A Instances of class B and classic are also loaded to Memory classB classe x=5 mClint=6 6- öne" ml): Int= n(): Intay Here mc) is overriden class

the Here m() in at m() base noen overides class when time method called If object is created for class B, then methods called using this object are from class B. Similarly object is created for class c , then class ' methods are called new for ex: val obj = new BC) H obj.mc This calls function mc) from class B. In this manner the functions are called. "ew Note: objects are cannot be created for abstract classes that means abstract classes cannot be instantiated

In above code if A is instantiated val obj = new AC) we get an error steting "closs A is abstract cannot be Instantiated"