Differences between abstract classes and interfaces in C ++

In the previous article, I reprinted the answers from the father of C ++ regarding the interface implementation, and wrote them by myself. However, since I used C # To write some programs, I did not have a deep understanding of the abstract keyword, and the results suffered a lot, after reading a lot of information about the implementation of virtual functions, pure virtual functions, abstract classes, and interfaces, I will sort out the differences between them.

I. abstract classes and interfaces

Abstract class:Abstract classes are special classes, but cannot be instantiated (classes that define pure virtual functions are called abstract classes). In addition, they have other features of classes; the important thing is that abstract classes can include abstract methods, which are not supported by common classes, but can also include common methods. Abstract METHODS can only be declared in abstract classes and do not contain any implementations. The Derived classes must overwrite them. In addition, an abstract class can be derived from an abstract class. It can overwrite the abstract methods of the base class or overwrite them. If not, its derived class must overwrite them. Although you cannot define an instance of an abstract class, you can define its pointer, which is the focus of using an abstract class to implement interfaces.

Interface:An interface is a concept. It is implemented using abstract classes in C ++ and interfaces in C # and Java.

 

The interface is of reference type. It is similar to a class and has three similarities with the abstract class:

1. It cannot be instantiated;
2. contains an unimplemented method statement;
3. The derived class must implement unimplemented methods. The abstract class is an abstract method, and the interface is all members (not only the methods include other members );

In addition, interfaces have the following features:
In addition to methods, interfaces can also contain attributes, indexers, and events, and these members are defined as common. It cannot contain any other Members, such as constants, fields, constructors, destructor, and static members. A class can directly inherit multiple interfaces, but can only inherit one class (including abstract classes ).

 

Differences between abstract classes and interfaces:
1. class is the abstraction of objects. abstract classes can be understood as classes as objects. abstract classes are called abstract classes. the interface is just a behavior specification or provision. Microsoft's custom interface always carries the able field behind it to prove that it represents a class "I can do it... ". Abstract classes are more defined in a series of closely related classes, while interfaces are mostly classes with loose relationships but all implement certain functions.
2. The interface basically does not have any specific characteristics of inheritance. It only promises the methods that can be called;
3. A class can implement several interfaces at a time, but only one parent class can be extended.
4. interfaces can be used to support callback, but inheritance does not.
5. the abstract class cannot be sealed.
6. The specific methods implemented by abstract classes are virtual by default, but the interface methods in the class implementing interfaces are non-virtual by default. Of course, you can also declare them as virtual.
7. Similar to a non-abstract class, an abstract class must provide its own implementation for all the members of the interface listed in the base class list of this class. However, the abstract class is allowed to map interface methods to abstract methods.
8. abstract classes implement a principle in OOP that separates mutable from immutable. Abstract classes and interfaces are defined as immutable classes, while variable class classes are implemented.
9. A good interface definition should be specific and functional, rather than multi-functional, otherwise it will cause interface pollution. If a class only implements a function of this interface and has to implement other methods in the interface, it is called interface pollution.
10. Avoid using inheritance to implement the build function, but use black box multiplexing, that is, object combination. As the hierarchy of inheritance increases, the most direct consequence is that when you call a class in this group, you must load all of them into the stack! The consequences can be imagined (based on the stack principle ). At the same time, some interested friends can note that Microsoft often uses the object combination method when building a class. For example, in Asp.net, the page class has server request and other attributes, but in fact they are all objects of a certain class. This object of the page class is used to call the methods and attributes of other classes. This is a very basic design principle.
11. If an abstract class implements an interface, you can map the methods in the interface to the abstract class as an abstract method without having to implement it. Instead, you can implement the methods in the subclass of the abstract class.

 

From: http://blog.csdn.net/bmzyDream_007/archive/2009/05/07/4157560.aspx