Abstract classes and interfaces

 

One . abstract class

1、 Definition

Why：

Calculator class （ Parent class ） There are four functions of addition, subtraction, multiplication and division , But very subclasses inherit , Some methods have been rewritten by themselves , At this time, the functions of these methods in the parent class are meaningless . So some methods don't need to be implemented , Just declare （ Abstract method ）.

abstract class （what）： A class is an abstraction with the same characteristics and behavior , And the abstract class （class with abstract） Didn't point out the specific details of the behavior , And its subclasses implement the corresponding behavior .

Add a before the general class abstract Keywords are abstract classes .

A class containing one or more abstract methods

3、 The abstract class features ：

1、 Cannot create an instance of an abstract class .（//Father f = new Father();Father Parent class ）

2、 By placing keywords before class definitions sealed, You can declare a class as a sealed class . When a class is declared sealed when , It cannot be inherited . An abstract class cannot be declared sealed.

4、 Abstract method characteristics ：

1、 Abstract methods have no method bodies

2、 Abstract methods must be in abstract classes

3、 Abstract methods must be implemented in subclasses , Unless the subclass is an abstract class

Two . Interface

C： Process oriented

C#、java、C++： object-oriented

1. Definition

C# Whether multiple inheritance is supported ？

yes . Classes can only be inherited singly , Interfaces support multiple inheritance

Why：

Interface ： Designate a group of Method Members without implementing their reference types

           Used to describe a set of common methods （ attribute ）, There is no implementation of the method
          Defining methods cannot add any access modifiers , Default public . You cannot add static static
          What can be defined ： Method , attribute , event , Indexer
          Undefined content ： Field , operator overloading , instant constructor , Destructor

There is an inheritance relationship between classes （ use ：（ The colon ））, The relationship between classes and interfaces is implementation （ use ：（ The colon ））

2.    Implicit call ： There is no method to specify which interface to implement Single interface   Classes and interfaces can access methods
      Display call ： Class implements multiple interfaces , And the interface contains methods with the same signature   It can only be accessed through the interface

3. Interface features

1、 Interfaces cannot be instantiated

2、 The implementation class must implement all methods of the interface

3、 Implementation classes can implement multiple interfaces

4、 Variables in an interface are static constants

4. The difference between abstract classes and interfaces

1. The keywords used are different Can't instantiate , Implement methods through inheritance
2. Interface support ” Multiple inheritance “, Abstract classes cannot implement
3. The definition content and method are different
4. Interface supports callback , Abstract classes cannot , Because inheritance doesn't support

5. Abstract classes need to use override Realization