PHP单件模式

<?php
/**
 *单件模式
 */
class Singleton {
        private static $instance = null;
        private $_field = null;
    
        public static function getInstance(){
                if(self::$instance == null)
                        self::$instance = new self();
                return self::$instance;
        }   

        /** 
         *私有化构造函数和对象复制
         */
        private function __clone(){}
        private function __construct(){}
        private function Singleton(){}
    
        /** 
         *成员函数
         */
        public function setField($field){
                $this->field = $field;
        }   
        public function getField(){
                return $this->field;
        }   
}

/**
 *test
 */

$obj_1 = Singleton::getInstance();
$obj_2 = Singleton::getInstance();

$obj_1->setField('hello');
echo $obj_2->getField();

echo "<br/>";
$obj_2->setField('world');
echo $obj_1->getField();
?>

　　输出：

hello

world