Abstract classes

We can define abstract classes using the abstract keyword:

abstract class Person 
class Customer extends Person 
class Employee extends Person 

Here, what we wanted was two subclasses that can also be treated as instances of a superclass, in our case, Person. For now, we have not shown any behavior in our abstract class. But, there are times when we want to imply some behaviors in our abstract classes that subsequent subclasses can inherit and define for themselves:

abstract class Person(category: String) { 
  val idPrefix: String 
} 
 
class Customer extends Person("External") { 
  override val idPrefix: String = "CUST" 
} 
 
class Employee extends Person("Internal") { 
  override val idPrefix: String = "EMP" 
} 

Our intention to use abstract classes is clearer now. We may want a set of classes that inherit methods...