PHP abstract class, php abstraction

For PHP programmers, the most difficult point to master is the application of PHP abstract classes. As a novice, I am not yet ready to use object-oriented knowledge to program, but in the future, it is inevitable to use classes to encapsulate or use interfaces to develop programs in various modular formats.

In natural language, we understand abstract concepts as a large description of an object, which is a common characteristic for a certain type of object. The same is true in PHP. When we abstract a class, we can indicate the general behavior of the class. This class should be a template, which indicates some behaviors that its sub-methods must implement.

Definition of PHP abstract class application:

abstract class ClassName{

}

Key points for PHP abstract class application:

1. Define some methods. Subclasses must fully implement all methods in this abstraction

2. Objects cannot be created from abstract classes, their meaning is to be extended

　3.Abstract classes usually have abstract methods, and there are no curly braces in the methods

Key points of PHP abstract class application:

1. Abstract methods do not have to implement specific functions, and are completed by subclasses

2. When a subclass implements a method of an abstract class, the visibility of the subclass must be greater than or equal to the definition of the abstract method

3. Methods of abstract classes can have parameters or be empty

4. If the abstract method has parameters, then the implementation of the subclass must also have the same number of parameters

PHP abstract class application example:

abstract public function_name(); //Note there are no curly brackets

PHP abstract class rules:

As a demonstration, let's implement a simple abstract class: calculate the area of ??a rectangle. This rectangle can be extended from the shape class.

< ?<span>PHP   
</span><span>abstract</span> <span>class</span><span> Shape {   
</span><span>abstract</span> <span>protected</span> <span>function</span><span> get_area();   
</span><span>//</span><span>和一般的方法不同的是，這個(gè)方法沒有大括號(hào)   
//你不能創(chuàng)建這個(gè)抽象類的實(shí)例：$Shape_Rect</span>= <span>new</span><span> Shape(); 
}   
</span><span>class</span> Rectangle <span>extends</span><span> Shape{   
</span><span>private</span> <span>$width</span><span>;   
</span><span>private</span> <span>$height</span><span>;   
</span><span>function</span> __construct(<span>$width</span>=0,
<span>$height</span>=0<span>){   

　　</span><span>$this</span>->width=<span>$width</span><span>;   
</span><span>　　$this</span>->height=<span>$height</span><span>;   
}   
</span><span>function</span><span> get_area(){   
</span><span>　　echo</span> (<span>$this</span>->width+<span>$this</span>->height)*2<span>;   
}   
}   
</span><span>$Shape_Rect</span> = <span>new</span> Rectangle(20,30<span>);   
</span><span>$Shape_Rect</span>-><span>get_area();   
</span>?>   

This is also a simple example, which basically illustrates the usage of abstract classes in PHP. I don’t want to say more about the rest. Personally, I think abstract classes are generally used in large projects, because I think it has too many "rules" to abide by, making it inconvenient to use! Of course this is just my opinion. I would like to say something more. PHP abstract class applications are single-inherited, which means that you can only inherit from one class, but not one class that inherits class A and class B. If you want to implement such a function, you have to use an interface. Related knowledge, I will not discuss the knowledge of PHP interface for the time being! In a word: Single inheritance and multiple interfaces!