单例模式

单例模式

<?php
/**
 * 单例模式
 *
 * @author T.L.Q. emali<hjq_tlq@163.com>
 */
class Single {
    private static $_instance = NULL;
   
    // 私有化构造方法，防止被类被实例化（
    private function __construct()
    {
        echo "construct<br />";
    }
   
    // 得到该类独一无二的实例
    public static function instance()
    {
        if (!self::$_instance instanceof Single) {
            self::$_instance = new Single();
        }
        return self::$_instance;
    }
   
    // 自定义方法
    public function test()
    {
        echo "OK<br />";
    }
   
    // 阻止用户复制对象实例
    public function __clone()
    {
        trigger_error('Clone is not allowed.', E_USER_ERROR);
    }
}
// 该类无法实例化，必须通过instance获得该类的实例
//$single = new Single();
$class = 'Single';
$single = $class::instance();
// 如果使用克隆则会抛出异常
//$singleClone = clone $single;
$single->test();
$single1 = $class::instance();
$single1->test();
$single2 = $class::instance();
$single2->test();
$single3 = $class::instance();
$single3->test();
$single4 = $class::instance();
$single4->test();
$single5 = $class::instance();
$single5->test();
$single6 = $class::instance();
$single6->test();
$single7 = $class::instance();
$single7->test();
// 结果
/*
construct
OK
OK
OK
OK
OK
OK
OK
OK
*/