What is the function of constructor method in php

The function of the constructor method "__construct()" in php is to initialize the object when creating the object, that is, assign initial values ​​to the object member variables. It is always used together with the new operator in the statement to create the object; syntax "public function __construct(parameter list){...}".

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

PHP __construct() : Constructor/method

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

The usage in PHP3.0 and PHP4.0 is abandoned 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 function of the PHP constructor is to initialize the object when creating the object, that is, to assign initial values ​​to the object member variables. It is always used together with the new operator in the statement to create the object. A special class can have multiple constructors, which can be distinguished based on the number of parameters or parameter types, that is, the overloading of the constructor.

Syntax:

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 its display. The code is as follows:

<?php
header("Content-type:text/html;charset=utf-8");
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;构造方法&#39;);
?>

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