PHP之设计模式（工厂、单例）

设计模式简单说应对某类问题而设计的解决方式

工厂模式：应对需求创建相应的对象

class factory{
    function __construct($name){
        if(file_exists('./'.$name.'.class.php')){
            return new $name;
        }else{
            die('not exist');
        }
    }
}

单例模式：只创建一个对象的实例，不允许再创建实例，节约资源（例如数据库的连接）

class instance{
    public $val = 10;
    private static $instance ;
    private function __construct(){}
    private function __clone(){}
    //设置为静态方法才可被类调用
    public static function getInstance(){
        /*if(!isset(self::$instance)){ self::$instance = new self; }*/
        if(!isset(instance::$instance)){
            instance::$instance = new self;
        }
        return instance::$instance;
    }
}

$obj_one = instance::getInstance();
$obj_one->val = 20;
//clone可以调用__clone()克隆即new出一个新的的对象
//$obj_two = clone $obj_one;
$obj_two = instance::getInstance();
echo $obj_two->val;
echo '<p>';
var_dump($obj_one,$obj_two);

应用：数据库连接类（database access oject）

class mysqldb{
    private $arr = array(
        'port' => 3306,
        'host' => 'localhost',
        'username' => 'root',
        'passward' => 'root',
        'dbname' => 'instance',
        'charset' => 'utf8'
         );
    private $link;
    static $instance;
    private function __clone(){}
    private function __construct(){
        $this->link = mysql_connect($this->arr['host'],$this->arr['username'],$this->arr['passward']) or die(mysql_error());
        mysql_select_db($this->arr['dbname']) or die('db error');
        mysql_set_charset($this->arr['charset']);
    }
    static public function getInsance(){
        if(!isset(mysqldb::$instance)){
            mysqldb::$instance = new self;
        }
        return mysqldb::$instance;
    }
    public function query($sql){
        if($res = mysql_query($sql)){
            return $res;
        }return false;
    }
    //fetch one
    public function get_one($sql){
        $res = $this->query($sql);
        if($result = mysql_fetch_row($res)){
            return $result[0];
        }
    }
    //fetch row
    public function get_row($sql){
        $res = $this->query($sql);
        if($result = mysql_fetch_assoc($res)){
            return $result;
        }
        return false;
    }
    //fetch all
    public function get_all($sql){
        $res = $this->query($sql);
        $arr = array();
        while($result = mysql_fetch_assoc($res)){
            $arr[] = $result;
        }
        return $arr;
    }
}
$mysql = mysqldb::getInsance();