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HomeBackend DevelopmentPHP Tutorialphp构造函数实例讲解_php技巧

PHP官网定义:

复制代码 代码如下:

构造函数是类中的一个特殊函数,当使用 new 操作符创建一个类的实例时,构造函数将会自动调用。当函数与类同名时,这个函数将成为构造函数。如果一个类没有构造函数,则调用基类的构造函数,如果有的话,则调用自己的构造函数

如a.php一个class a类:
复制代码 代码如下:

class a{
 function __construct(){
  echo 'class a';
 }
}

b.php有个class b类继承a类:
复制代码 代码如下:

include 'a.php';
class b extends a{
 function __construct(){
  echo '666666';
  //parent::__construct();
 }

 function index(){
  echo 'index';
 }
}
 

$test=new b();
这样写的话,b类有自己的构造函数,那么实例化b类的时候,自动运行构造函数,此时默认不运行父类的构造函数,如果同时要运行父类构造函数,要声明parent::__construct();
复制代码 代码如下:

include 'a.php';
class b extends a{
 function index(){
  echo 'index';
 }
}
 

$test=new b();
此时b类没有自己的构造函数,那么将默认执行父类的构造函数。
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