PHP implements singleton mode supplemented by calling instructions

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<?php
class Sim{
    //测试对象的值
    private $age = &#39;&#39;;
    //本类的一个对象
    private static $instance = null;
    //构造函数私有化 防止外部 new
    private function __construct($age)
    {
        $this->age = $age;
    }
    //禁止外部克隆
    private function __clone()
    {

    }
    //开放对外接口。
    public static function getInstance($age){
        if(!self::$instance instanceof self)
        {
            self::$instance = new self($age);
        }
        return self::$instance;
    }
    //测试打印
    public function showValue(){
        echo $this->age.&#39;<br>&#39;;
    }

}

$sim = Sim::getInstance(3);
$sim->showValue();
//重新赋值 并没有影响原来的对象属性值 可见是同一个对象在共享数据，以此来说明 单例
$sim = Sim::getInstance(3332);
$sim->showValue();

Print test results

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