php单例模式(SingletonPattern)实例教程

2. class DatabaseConnection {
3. private static $db;
4. private static $_handle = null;
6. public static function get() {
7. if ( self::$db == null ){
8. echo __LINE__;
9. self::$db = new DatabaseConnection();
10. }
11. return self::$_handle;
12. }
14. private function __construct() {
15. $dsn = 'mysql://root:password@localhost/photos';
16. self::$_handle = 123;
17. }
19. }
21. print( "Handle = ".DatabaseConnection::get()."\n" );
22. print( "Handle = ".DatabaseConnection::get()."\n" );
23. ?>

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

例2，php单例模式。

2. class DatabaseConnection
3. {
4. public static function get()
5. {
6. static $db = null;//此处将示例1的静态成员变为静态变量
7. if ( $db == null ){
8. echo __LINE__;
9. $db = new DatabaseConnection();
10. }
11. return $db;
12. }
14. private $_handle = null;//此处将表示示例1的静态去除
16. private function __construct()
17. {
18. $dsn = 'mysql://root:password@localhost/photos';
19. $this->_handle =123;
20. }
21. //此处新增获取私有成员$_handle的方法
22. public function handle()
23. {
24. return $this->_handle;
25. }
26. }
28. print( "Handle = ".DatabaseConnection::get()->handle()."\n" );
29. print( "Handle = ".DatabaseConnection::get()->handle()."\n" );
30. ?>

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

2. class DatabaseConnection {
3. public static function get($persistent_id=0) {//传入一个标识
4. static $db = array();//此处改为数组
5. if ( !array_key_exists($persistent_id, $db) ) {
6. echo __LINE__;
7. $db[$persistent_id] = new DatabaseConnection();
8. }
9. return $db[$persistent_id];
10. }
12. private $_handle = null;
14. private function __construct() {
15. $dsn = 'mysql://root:password@localhost/photos';
16. $this->_handle =123;
17. }
18. //此处新增获取私有成员$_handle的方法
19. public function handle() {
20. return $this->_handle;
21. }
22. }
24. print( "Handle = ".DatabaseConnection::get(1)->handle()."\n" );
25. print( "Handle = ".DatabaseConnection::get(2)->handle()."\n" );
26. print( "Handle = ".DatabaseConnection::get(2)->handle()."\n" );
27. ?>

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。