1. Chapter 12 OOP: Polymorphism, Interfaces and Operator Overloading

2. 12.2 Polymorphism Examples

3. By example: Polymorphic Employee Inheritance Hierarchy
Simple payroll application that polymorphically and dynamically calculates the weekly pay of several different types of employees using each employee’s Earnings method.
Though the earnings of each type of employee are calculated in a specific way, polymorphism allows us to process the employees “in the general.”
Two new classes — SalariedEmployee (for people paid a fixed weekly salary) and HourlyEmployee (for people paid an hourly salary and “time-and-a-half” for overtime).

4. By example: Polymorphic Employee Inheritance Hierarchy cont
common set of functionality for all the classes in the updated hierarchy in an “abstract” class, Employee, from which classes SalariedEmployee, HourlyEmployee and
CommissionEmployee inherit directly and class BasePlusCommissionEmployee inherits indirectly.
=> invoke each employee’s Earnings method off a base class
Employee reference, the correct earnings calculation is performed
due to C#’s polymorphic capabilities.

5. 12.3 Demonstrating Polymorphic Behavior

7. Base class
Derived class

8. Same

9. 12.4 Abstract Classes and Methods

10. Determining the Type of an Object at Execution Time
Occasionally, when performing polymorphic processing, we need to program “in the specific.”
Employee case study demonstrates that an application can determine the type of an object at execution time and act on that object accordingly. In the case study, we use these capabilities to determine whether a particular employee object is a
BasePlusCommissionEmployee.
As the result employee’s base salary is increased by 10%.

11. 12.5 Case Study: Payroll System Using Polymorphism

13. override/virtual method1_derived method2_derived method1_base
public class Base
{public class Base {
public string method1() { return "method1_base"; }
public virtual string method2() { return "method2_base"; } }
public class Derived : Base
public static void Main(string[] args) method1_derived
Derived derived = new Derived();
Console.WriteLine(derived.method1());
Console.WriteLine(derived.method2());
Console.WriteLine(derived.method3());
Console.WriteLine(derived.method4());
public string method1() { return "method1_derived"; } //hiding
public override string method2() { return "method2_derived"; }
public string method3() { return base.method1(); }
public string method4() { return base.method2(); }
method1_derived
method2_derived
method1_base
method2_base

36. sealed Methods
When an instance method declaration includes a sealed modifier, that method is said to be a sealed method. If an instance method declaration includes the sealed modifier, it must also include the override modifier. Use of the sealed modifier prevents a derived class from further overriding the method.
using System;
class A {
public virtual void F() {
Console.WriteLine("A.F"); }
public virtual void G() {
Console.WriteLine("A.G");
class B: A
sealed override public void F() {
Console.WriteLine("B.F");
override public void G() {
Console.WriteLine("B.G");
class C: B
Console.WriteLine("C.G");

37. 12.6 sealed Methods and Classes
Sealed method in a base class cannot be overridden in a derived class.
private methods implicitly sealed
static methods implicitly sealed
Class sealed cannot be a base class

38. 12.7 Case Study: Creating and Using Interfaces

40. implements

54. 12.8 Operator Overloading