php单例模式(Singleton Pattern)实例教程

程序员文章站 2022-05-01 19:29:08

...

class DatabaseConnection {
private static $db;
private static $_handle = null;
public static function get() {
if ( self::$db == null ){
echo __LINE__;
self::$db = new DatabaseConnection();
}
return self::$_handle;
}
private function __construct() {
$dsn = 'mysql://root:password@localhost/photos';
self::$_handle = 123;
}
}
print( "Handle = ".DatabaseConnection::get()."\n" );
print( "Handle = ".DatabaseConnection::get()."\n" );
?>

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9Handle = 123 Handle = 123 [Finished in 0.1s]

例2，php单例模式。

class DatabaseConnection
{
public static function get()
{
static $db = null;//此处将示例1的静态成员变为静态变量
if ( $db == null ){
echo __LINE__;
$db = new DatabaseConnection();
}
return $db;
}
private $_handle = null;//此处将表示示例1的静态去除
private function __construct()
{
$dsn = 'mysql://root:password@localhost/photos';
$this->_handle =123;
}
//此处新增获取私有成员$_handle的方法
public function handle()
{
return $this->_handle;
}
}
print( "Handle = ".DatabaseConnection::get()->handle()."\n" );
print( "Handle = ".DatabaseConnection::get()->handle()."\n" );
?>

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8Handle = 123 Handle = 123 [Finished in 0.1s] 这两个示例个人偏好第二个四。限度可生成实例的个数

class DatabaseConnection {
public static function get($persistent_id=0) {//传入一个标识
static $db = array();//此处改为数组
if ( !array_key_exists($persistent_id, $db) ) {
echo __LINE__;
$db[$persistent_id] = new DatabaseConnection();
}
return $db[$persistent_id];
}
private $_handle = null;
private function __construct() {
$dsn = 'mysql://root:password@localhost/photos';
$this->_handle =123;
}
//此处新增获取私有成员$_handle的方法
public function handle() {
return $this->_handle;
}
}
print( "Handle = ".DatabaseConnection::get(1)->handle()."\n" );
print( "Handle = ".DatabaseConnection::get(2)->handle()."\n" );
print( "Handle = ".DatabaseConnection::get(2)->handle()."\n" );
?>

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6Handle = 123 6Handle = 123 Handle = 123 [Finished in 0.1s] 补充，利用static静态化的方法使我们可以轻松地实现php的单例模式。当然也可以使用全局变量存储，但是这种方法仅适用于较小的应用程序。在较大的应用程序中，应避免使用全局变量，并使用对象和方法访问资源。