Recall Subclass and Inheritance

• A subclass extends a parent class.
• Subclass inherits instance variables and methods from the parent class.
• Subclasses cannot see private components of parent class.
• Subclass can add more instance variables and methods.

• Subclass can also OVERRIDE methods.

  • Manager can redefine bonus() defined in the Employee class.

    

  • Uses parent class bonus() using super.

• Consider the following assignment:
  • Employee e = new Manager(...)
• Question : Can we invoke e.setSecretary ? NO (during compile time)
  • e is declared to be an Employee
  • And Employee does not have this method present (during compilation).
  • So e can only refer to methods of Employee .
• Question : Can we invoke e.bonus(p)? YES → Which bonus() do we use (Since Employee and Manager both have bonus() method)?
  • Since e is Employee , we can use all the methods in Employee class → So we can use bonus()
  • So at Static : Uses Employee.bonus()
  • But during run time, the object is a Manager stored in an Employee object → Uses Manager.bonus()
  • This is an illustration of the concept Dynamic Dispatch.
    • Default in Java, optional in language like C++ (virtual function)

Polymorphism

Consider the following code:

• Defined an array of Employees in which the first object is an Employee but the second object is a Manager.
• So when calling the bonus() method which each element :
  • It uses the correct bonus() function depending on whether the object is a Manager or Employee
• This is an illustration of the concept : Runtime Polymorphism or Inheritance Polymorphism

Functions, Signatures, Overloading