How to write php constructor

In PHP, the constructor is a special function in a class. The specific writing method is "public function __construct (parameter list) {...code...}"; the parameter list is optional. Can be omitted if not needed.

The operating environment of this tutorial: windows7 system, PHP7.1 version, DELL G3 computer

Constructor method (constructor method, also called constructor Constructor) is a special function in a class. When an object is instantiated using the new keyword, the constructor will be automatically called.

In PHP3.0 and PHP4.0, the constructor is a function with the same name as the class in which it is located. In PHP5, although the usage in PHP3.0 and PHP4.0 is also supported, it is more recommended to use __construct as the constructor of the class. The advantage of this is that the constructor does not need to be modified as the class name changes. The usage in PHP3.0 and PHP4.0 is obsolete in PHP7.0, and the constructor must be defined using __construct.

The constructor is the first function that is automatically called in the class when the object is created, and there can only be one constructor in a class. Similar to ordinary functions, constructors can also have parameters. If the constructor has parameters, then the corresponding parameters need to be passed in during instantiation, such as new Students ($name, $age).

The syntax format for creating a constructor is as follows:

public function __construct(参数列表){
    ... ...
}

Among them, the parameter list is optional and can be omitted if not needed.

If the constructor is not explicitly declared in the code, there will be a constructor with no parameter list and empty content in the class by default. If a constructor is declared explicitly then a default constructor will not exist in the class. Therefore, constructors are usually used to do some preparation work, such as assigning values ​​to certain parameters.

Note: If the constructor is declared explicitly, its access permission must be public, and the constructor is automatically called when instantiated, we do not need to call it manually.

[Example] Create a class and create a constructor for it to display. The code is as follows:

<?php
    class Website{
        public $name, $url, $title;
        public function __construct($str1, $str2, $str3){
            $this -> name  = $str1;
            $this -> url   = $str2;
            $this -> title = $str3;
            $this -> demo();
        }
        public function demo(){
            echo $this -> name.&#39;<br>&#39;;
            echo $this -> url.&#39;<br>&#39;;
            echo $this -> title.&#39;<br>&#39;;
        }
    }
    $object = new Website(&#39;PHP中文网&#39;,&#39;https://www.php.cn/&#39;,&#39;构造函数&#39;);
?>

The running results are as follows:

PHP中文网
https://www.php.cn/
构造函数

We used $this in the code , it represents the currently called object, and $this can only be used in class methods

Recommended learning: "PHP Video Tutorial"

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