Dynamic (Runtime) Polymorphism

There is another flavor of polymorphism called dynamic or runtime polymorphism where the Java Virtual Machine (JVM) decides at runtime which method to dispatch.

The dynamic polymorphism relates to the ability of a child class to override the behavior of its parent class.

Example: Consider the following classes

public class CourseAssistant {

  public double getBaseSalary() {
    return 500.00; //dollars
  }

  public double getHourlyPayRate() {
    return 15.00; // dollars
  }
}

public class ExperiencedCourseAssistant extends CourseAssistant {

  @Override
  public double getHourlyPayRate() {
    return 1.1 * super.getHourlyPayRate(); 
  }
}

The ExperiencedCourseAssistant inherits the methods getBaseSalary() and getHourlyPayRate() from CourseAssistant but it overrides the getHourlyPayRate() method to implement a 10% higher (than the base) pay rate.

Exercise Assume we have the following method

public double calcPayment(CourseAssistant ca, int hoursWorked) {
  return ca.getBaseSalary() + 
    hoursWorked * ca.getHourlyPayRate();
}

What does calcPayment return in the following cases?

CourseAssistant tom = new CourseAssistant();
CourseAssistant mona = new ExperiencedCourseAssistant();

calcPayment(tom, 10); 
calcPayment(mona, 10); 

(a) both call return $650$
(b) both call return $665$
(c) first call returns $650$ and second one returns $665$
(d) first call returns $665$ and second one returns $650$