The concept of C # polymorphism and its application

Polymorphism is one of the three mechanisms in object-oriented programming, and its principle is based on the rule that subclasses that inherit from the parent class can be converted to their parent class. In other words, you can use a parent class where you can use subclasses of that class. When many subclasses derive from the parent class, because each subclass has a different code implementation, So when using the parent class to refer to these subclasses, the same operation can be performed with different operating results, which is called polymorphism.

1. Understand what is C # polymorphism

2. How to define a virtual method

3. How to overload a virtual method

4. How to apply polymorphism in a program

Another important concept in object-oriented programming is C # polymorphism. At run time, you can invoke the method in the derived class by pointing to a pointer to the base class. You can put a group of objects into an array, and then call their methods, in which case the polymorphism is manifested, and these objects do not have to be the same type of object. Of course, if they all inherit from a class, you can put these derived classes into an array. If each of these objects has a method of the same name, you can call each object's method of the same name. This lesson will show you how to accomplish these things.

1. Listing 9-1. Base class with virtual method: DrawingObject.cs

using　System;
public　class　 DrawingObject
{
　　　　public　virtual　void　Draw()
　　　　{
　　　　　　　　Console.WriteLine("I'm　just　 a　generic　drawing　object.");
　　　　}
}

Description

Listing 9-1 defines the Drawingobject class. This is a base class that can be inherited by other objects. The class has a method named Draw (). The Draw () method has a virtual modifier that indicates that the derived class of the base class can overload the method. The Draw () method of the Drawingobject class accomplishes the following: Output statement "I ' m just a generic drawing object." to the console.

2. Listing 9-2. Derived classes with overloaded methods: Line.cs, Circle.cs, and Square.cs

using　 System;
public　class　Line　:　DrawingObject
{
　　　 　public　override　void　Draw()
　　　　{
　　　　　　　　 Console.WriteLine("I'm　a　Line.");
　　　　}
}

public　class　Circle　:　DrawingObject
{
　 　　　public　override　void　Draw()
　　　　{
　　　　　　 　　Console.WriteLine("I'm　a　Circle.");
　　　 　}
}

public　class　Square　:　DrawingObject
{
　　　　public　override　void　Draw()
　　　　{
　　 　　　　　　Console.WriteLine("I'm　a　Square.");
　　　　}
}

Description

Listing 9-2 defines three classes. All three classes derive from the Drawingobject class. Each class has a draw () method with the same name, and each of these draw () methods has an overloaded modifier. The overload modifier enables the method to overload its base class's virtual methods at run time by referencing the class by a pointer variable of the base class type.