Basic usage tutorial of php abstract class

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 that the abstract concept is 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 subclasses must fully implement all methods in this abstraction
　2 .Objects cannot be created from abstract classes, 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 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 that there are no braces
PHP abstract class rules:
As long as a class contains at least one abstract method, it must be declared as an abstract class
Abstract methods cannot contain
FunctionBodyInherit the subclass of the abstract class, and implement the abstract method, it must have the same or lower access level as the abstract method
Inherit the subclass of the abstract class, if you do not implement all Abstract method, 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.

Copy code The code is as follows:

<?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 much else. 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 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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