Understanding and function of polymorphism

One 、 What is polymorphism

   The definition of polymorphism in object-oriented ： It refers to providing a unified interface for entities with different data types .
   For example, there are animals （Animal） The category of （Class）, And animals inherit the class chicken （Chicken） And category dog （Dog）, And for animals of the same origin （ Parent class ） One message has a different response , For example, the category of animals has “ It's called ()” The action of , And the type of chicken will “ Cry ()”, Category dogs will “ bark ()”, It is called polymorphism .

Two 、 Polymorphic type

   Polymorphism can be divided into static polymorphism and dynamic polymorphism .

• Static polymorphism ： Implement polymorphism during compilation , The same method passes different parameters , Achieve different effects .

  C++ Code implementation ：

// print() function 
void print(const char* str,int width);
void print(double i ,int width);
void print(const char* str);
//  Use print() Function time , The compiler will use prototypes with corresponding characteristics according to the usage taken 
print("abc",12);
print(2.2,55);
print("def");

• Dynamic polymorphism ： Realize polymorphism during operation , A class reference can be assigned to different subclass objects .

   The necessary condition to realize dynamic polymorphism ：

• Programming languages should support inheritance
• Subclasses can override （override） Methods in the parent class
• Parent references can point to child objects

  C# Code implementation ：

public class AnimalFactory{
    
	public static Animal createAnimal(string type){
    
		Animal animla=null;
		switch(type){
    
			case "cat":
				animal=new Cat();
				break;
			case "bird":
				animal=new Bird();
				break;
			case "dog":
				animal=new Dog(); 
				break;
		}
	}
}

3、 ... and 、 What problem does polymorphism solve

1. The application does not have to write function calls for each subclass , Just process the parent class . Greatly improve the reusability of the program .
2. The function of the subclass can be called by the method or reference variable of the parent class , It's like Animal class , Can improve scalability and maintainability .