How to use php abstract class? Detailed explanation of usage of php abstract class definition

For PHP programmers, the most difficult point to master is the knowledge point of PHPAbstract classapplication. As a novice, I have not yet used the knowledge of Object-oriented to program, but in future development, I will use classes to encapsulate or use interfaces to develop programs in various modular formats. Of course, this It is inevitable.

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 of PHP abstract class application:

　1. Define some methods, and the subclass must fully implement all methods in this abstraction

　2. Objects cannot be created from the abstract class, its meaning is to be extended

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

PHP abstract class application key points:

1. Abstract methods do not need to implement specific The function is completed by the subclass

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

　3. The abstract class The method 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 that there are no braces

PHP abstract class rules:

1. A certain class only needs to be at least If it contains an abstract method, it must be declared as an abstract class

2. abstract method and cannot containfunctionbody

3. inheritance Subclasses of abstract classes that implement abstract methods must have the same or lower access level as the abstract method

4. Inherit subclasses of abstract classes. If they do not implement all abstract methods, Then this subclass is also an abstract class

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.

<?php
abstract class Shape {   
abstract protected function get_area();   
//和一般的方法不同的是，这个方法没有大括号   
//你不能创建这个抽象类的实例：$Shape_Rect= new Shape(); 
}   
class Rectangle extends Shape{   
private $width;   
private $height;   
function construct($width=0,$height=0){   

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

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 a few more things. 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!

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