abstract class

Preface

occasionally , Base classes are not related to specific things , But only express an abstract concept , It is used to provide a public interface for its derived classes . So ,C# Abstract classes are introduced in (abstract class) The concept of .
Abstract class cannot be instantiated . The purpose of abstract classes is to provide a common base class definition that can be shared by multiple derived classes . for example , A class library can define an abstract class , Use it as an argument to multiple class library functions , And ask the programmers who use the library to provide their own class implementation by creating derived classes . Abstract classes can also define abstract methods . The method is to put the keyword abstract Add to the front of the return type of the method .

keyword

1 keyword ：abstract: abstract
2 from abstract A modified class is called an abstract class , from abstract The method of modification is called abstract method .
3 If there are abstract methods in a class , The class must be abstract .
4 Abstract method ： If a method is an abstract method , The method must be in an abstract class . At the same time, abstract methods only have method declarations , There is no way to achieve . Abstract methods are implemented by subclasses that inherit abstract classes , That is, if a class inherits an abstract class , This class must implement all abstract methods in the abstract class . Rewrite abstract methods with override.
5 Abstract classes cannot instantiate objects .

---

Use abstract keyword public abstract bool Withdraw(…);
Abstract methods are methods that must be overridden by derived classes .
Abstract methods can be regarded as virtual methods without implementers
If the class contains abstract methods , Then class must be defined as abstract class , Whether or not other general methods are included
Virtual method
Use virtual keyword public virtual bool Withdraw(…);

---

Both virtual and abstract methods can be overridden by derived classes , What's the difference between them ？

1. Virtual methods must have an implementation part , The abstract method does not provide the implementation part , Abstract methods are methods that force derived class coverage , Otherwise, the derived class will not be instantiated .
2. Abstract methods can only be declared in abstract classes , The virtual method is not . In fact, if the class contains abstract methods , Then the class is also abstract , Must also be declared abstract .
3. Abstract methods must be overridden in derived classes ,
   . ***