PHP单例模式定义与使用实例详解

class DB{
   private $_link;
   //   保持单例类的静态变量
   static $_instance;
   //   私有的构造函数
   private function __construct(){
       $this->_link = @mysqli_connect(__HOST__, __USER__, __PASSWORD__, __DATABASE__);
       if(! ($this->_link)){
          echo 'Something wrong ours on the database connection!';  
       }
   }
   //   防止单例类被克隆
   private function __clone(){}
   //   外界访问单例类实例的接口
   public static function getInstance(){
       if(! (self::$_instance instanceof self)){
          self::$_instance = new self();
       }
       return self::$_instance;
   }
}

class DB {
   /
     the database connection
     @var   resource
     @aess private
    /
   private $_link;
   /
     the static instance of single db
     @var   object
     @aess static
    /
   static $_instance;
   /
     construct the single object
     @return null
     @aess private
    /
   private function __construct(){
       $this->_link = @mysqli_connect(__HOST__, __USER__, __PASSWORD__, __DATABASE__);
       if(! ($this->_link)){
          echo 'Something wrong ours on the database connection!';  
       }
   }
   /
     empty clone
     @return null
     @aess private
    /
   private function __clone(){}
   /
     for other object to get the instance of db
     @return self::instance
     @aess public
    /
   public static function getInstance(){
       if(! (self::$_instance instanceof self)){
          self::$_instance = new self();
       }
       return self::$_instance;
   }
   /
     query
     @param  sql string
     @param  message string
     @return   resource
     @aess public
    /
   public function query($sql,$message){
       $result = @mysqli_query($this->$_link, $sql) or die($message . mysqli_error($this->$_link));
       return $result;
   }
   /
     mysqli_num_rows
     @param  result resource
     @return   int
     @aess public
    /
   public function num($result){
       return @mysqli_num_rows($result);
   }
   /
     mysqli_fetch_array
     @param  result resource
     @return   array
     @aess public
    /
   public function fetchArr($result){
       return @mysqli_fetch_array($result);
   }
   /
     mysqli_insert_id
     @return   int
     @aess public
    /
   public function last_id(){
       return @mysqli_insert_id($this->_link);   
   }
   /
     close the database connection
     @param  result resource
     @return   null
     @aess public
    /
   public function close(){
       @mysqli_close($this->_link);
   }
   /
     fetch once result from the specific sql query
     @param  sql string
     @param  message string
     @return   array
     @aess public
    /
   public function fetchArrOnce($sql, $message){
       $result = $this->query($sql, $message);
       $row = $this->fetchArr($result);
       return $row;
   }
   /
     fetch all results from the specific sql query
     @param  sql string
     @param  message string
     @return   array
     @aess public
    /
   public function fetchArrMore($sql, $message){
       $result = $this->query($sql, $message);
       $moreRow = array();
       while($row = $this->fetchArr($result)){
          $moreRow[] = $row;
       }
       return $moreRow;
   }
   /
     fetch the number of results from the specific sql query
     @param  sql string
     @param  message string
     @return   array
     @aess public
    /
   public function fetchNum($sql, $message){
       $result = $this->query($sql, $message);
       $resultNum = $this->num($result);
       return $resultNum;
   }
   /
     mysqli_prepare
     @param  sql string
     @return   stmt object
     @aess public
    /
   public function prepare($sql){
       return @mysqli_prepare($this->_link, $sql);
   }
   /
     mysqli_stmt_execute
     @param  stmt object
     @param  message string
     @return   bool
     @aess public
    /
   public function stmt_execute($stmt, $message){
       @mysqli_stmt_execute($stmt) or die($message . mysqli_error($this->_link));
   }
}

define("__HOST__", "localhost");
define("__USER__", "root");
define("__PASSWORD__", "");
define("__DATABASE__", "eee");
$db = DB::getInstance();