What are the php constructors?

The php constructor is a special method, mainly used to initialize the object when creating the object; that is, assign initial values ​​to the object member variables, and is always used together with the new operator in the statement to create the object.

When using the new operator to create an instance of a class, the constructor (method) will be automatically called, and its name must be __construct().

Only one constructor can be declared in a class, but the constructor will only be called once every time an object is created. This method cannot be called actively, so it is usually used to perform some useful initialization. Task. This method has no return value.

Grammar:

function __construct(arg1,arg2,...)
{
    ......
}

demo:

<?php
/**
 * Created by PhpStorm.
 * User: liudandan
 * Date: 2018/5/13
 * Time: 11:50
 */
class BaseClass {
    function __construct() {
        print "我是构造函数\n";
    }
}

class SubClass extends BaseClass {
    function __construct() {
        parent::__construct();
        print "我是 SubClass 下的构造函数\n";
    }
}

class OtherSubClass extends BaseClass {

}


$obj = new BaseClass();
$obj = new SubClass();
$obj = new OtherSubClass();

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