PHP abstract classes introduction

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 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

Key points of PHP abstract class application:
　 1. Abstract methods do not have to implement specific functions, and are completed by subclasses
　 2. In 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. The method of the abstract class can have parameters or be empty
4. If the abstract method has parameters, then the subclass The implementation 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 Declared as an abstract class
Abstract methods cannot contain function bodies
Inherit the subclass of the abstract class, and implement the abstract method, must have the same or lower access level as the abstract method
Inherit the subclass of the abstract class, if it is not implemented 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.

. The code is as follows:

< ?PHP
abstract class Shape {
abstract protected function get_area();
//Unlike the general method, this method does not have curly brackets
//You cannot create this Example of abstract class: $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!

The above is the introduction of PHP abstract classes. For more related articles, please pay attention to the PHP Chinese website (www.php.cn)!