The difference between PHP abstract classes and interfaces

1, PHP interface class: interface

In fact, their role is very simple, when a lot of people to develop a project, it may be to call someone else to write some of the classes, then you will ask, how do I know how the implementation of one of his functions is named, this time the PHP interface class will play a role, when we define an interface class, The way inside it is that the following subclass must be implemented, such as:
The code is as follows:

I declare a shop interface class, defines three methods: Buy, Sell (Sell), see (view), then inherit all subclasses of this class must implement these 3 methods less than one, if the subclass does not implement these words, it will not run. In fact, the interface class is plainly, is a class template, a class of provisions, if you belong to this category, you have to follow my rules, less one can not, but specific how you do, I don't care, it is your business, such as:
The code is as follows:

You think, in a multi-person cooperation of large projects, with the interface class is how convenient, so you do not have to ask others, your method name of the function is what, of course, if you like this I have no way.
Conclusion: The interface class is the leader of a class, indicating the direction in which the subclass must complete its specified method.

2, PHP abstract class:

In fact, the abstract class and interface classes are very similar, remember where to see such a sentence, the abstract class like the part of the extraction, this looks very funny, in fact, it said the abstract class of truth, the role of abstract classes, when you find many of your classes in a lot of ways you constantly in the repeated writing, Then you can consider using the abstract class, you might say "I can not rewrite a class each public class I instantiate a public class, call the same method can be," Here is OK, actually the abstract class does the work of this, but he omitted you instantiate this step, It's as handy as calling this method directly, and you can overload the method. Such as:
The code is as follows:

Here is an example, like the above I define a store class, pull out all of its like, buy, sell (Sell), look (view), and the abstract class has implemented these methods, then inherit its subclasses automatically obtained these methods, subclasses do its own unique things, Introduce the duplication of code and improve reusability.

Conclusion:

Abstract class is a class of service providers, with a number of services, you do not have to use, when needed when you can use, if you feel not to provide services are not satisfied, you can also do it yourself.

Difference:
1, the use of the interface is through the keyword implements. The use of abstract classes is through the keyword extends. Of course the interface can also be inherited by the keyword extends.

2. You cannot declare member variables (including class static variables) in an interface, but you can declare class constants. Abstract classes can declare various types of member variables to implement the encapsulation of data. (The member variables in the Java interface are declared as public static final type)

3, interfaces do not have constructors, abstract classes can have constructors.

4, the method in the interface is the public type by default, and the methods in the abstract class can be decorated with private,protected,public.

5. A class can implement multiple interfaces at the same time, but a class may inherit only one abstract class.

An abstract class or an interface.
If you are creating a model, this model will be used by some closely related objects, and you can use abstract classes. The interface is used if you want to create features that will be used by some unrelated objects.
If the behavior must be inherited from multiple sources, the interface is used.
If you know that all classes share a common behavior implementation, use an abstract class and implement that behavior in it.

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