<?php//單列模式// //1.普通類// class singleton{// }// $s1 = new singleton();// $s2 = new singleton();// //注意，2個(gè)變量是同1個(gè)對(duì)象的時(shí)候才全等// if ($s1 === $s2) {//   echo '是一個(gè)對(duì)象';// }else{//   echo '不是一個(gè)對(duì)象';// }// //2.封鎖new操作// class singleton{//   protected function __construct(){}// }// $s1 = new singleton();//PHP Fatal error: Call to protected singleton::__construct()// //3.留個(gè)接口來new對(duì)象// class singleton{//   protected function __construct(){}//   public static function getIns(){//     return new self();//   }// }// $s1 = singleton::getIns();// $s2 = singleton::getIns();// if ($s1 === $s2) {//   echo '是一個(gè)對(duì)象';// }else{//   echo '不是一個(gè)對(duì)象';// }// //4.getIns先判斷實(shí)例// class singleton{//   protected static $ins = null;//   private function __construct(){}//   public static function getIns(){//     if (self::$ins === null) {//       self::$ins = new self();//     }//     return self::$ins;//   }// }// $s1 = singleton::getIns();// $s2 = singleton::getIns();// if ($s1 === $s2) {//   echo '是一個(gè)對(duì)象';// }else{//   echo '不是一個(gè)對(duì)象';// }// //繼承// class A extends singleton{//   public function __construct(){}// }// echo '<br>';// $s1 = new A();// $s2 = new A();// if ($s1 === $s2) {//   echo '是同一個(gè)對(duì)象';// }else{//   echo '不是同一個(gè)對(duì)象';// }// //5.防止繼承時(shí)被修改了權(quán)限// class singleton{//   protected static $ins = null;//   //方法加final則方法不能被覆蓋，類加final則類不能被繼承//   final private function __construct(){}//   public static function getIns(){//     if (self::$ins === null) {//       self::$ins = new self();//     }//     return self::$ins;//   }// }// $s1 = singleton::getIns();// $s2 = singleton::getIns();// if ($s1 === $s2) {//   echo '是同一個(gè)對(duì)象';// }else{//   echo '不是同一個(gè)對(duì)象';// }// //繼承// // class A extends singleton{// //   public function __construct(){}// // }// //Cannot override final method singleton::__construct()// echo '<hr>';// $s1 = singleton::getIns();// $s2 = clone $s1;// if ($s1 === $s2) {//   echo '是同一個(gè)對(duì)象';// }else{//   echo '不是同一個(gè)對(duì)象';// }//6.防止被cloneclass singleton{  protected static $ins = null;  //方法加final則方法不能被覆蓋，類加final則類不能被繼承  final private function __construct(){}  public static function getIns(){    if (self::$ins === null) {      self::$ins = new self();    }    return self::$ins;  }  // 封鎖clone  final private function __clone(){}}$s1 = singleton::getIns();$s2 = clone $s1; //Call to private singleton::__clone() from contextif ($s1 === $s2) {  echo '是同一個(gè)對(duì)象';}else{  echo '不是同一個(gè)對(duì)象';}