{"id":109,"date":"2021-03-08T00:21:19","date_gmt":"2021-03-08T00:21:19","guid":{"rendered":"https:\/\/phptutorial.net\/?page_id=109"},"modified":"2025-04-07T11:32:19","modified_gmt":"2025-04-07T11:32:19","slug":"php-static-methods","status":"publish","type":"page","link":"https:\/\/www.phptutorial.net\/php-oop\/php-static-methods\/","title":{"rendered":"PHP Static Methods and Properties"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you will learn about PHP static methods and static properties and understand the differences between the  $this<\/code> and self<\/code>.<\/p>\n\n\n\n

Introduction to PHP static methods and properties #<\/a><\/h2>\n\n\n\n

So far, you have learned how to define a class<\/a> that consists of methods and properties. To use the methods and properties of the class, you create an object and access these methods and properties via the object.<\/p>\n\n\n\n

Since these methods and properties are bound to an instance of the class, they are called instance methods and properties.<\/p>\n\n\n\n

PHP allows you to access the methods and properties in the context of a class rather than an object. Such methods and properties are class methods and properties.<\/p>\n\n\n\n

Class methods and class properties are called static methods and properties.<\/p>\n\n\n\n

Static methods #<\/a><\/h3>\n\n\n\n

To define a static method, you place the static<\/code> keyword in front of the function<\/code> keyword as follows:<\/p>\n\n\n

\n<?php<\/span>\n\nclass<\/span> MyClass<\/span>\n<\/span>{\n\tpublic<\/span> static<\/span> function<\/span> staticMethod<\/span>()<\/span>\n\t<\/span>{\n\t}\n}\n<\/span><\/code><\/span>Code language:<\/span> HTML, XML<\/span> (<\/span>xml<\/span>)<\/span><\/small><\/pre>\n\n\n
Since a static method is bound to a class, not an individual instance of the class, you cannot access $this<\/code> inside the method. However, you can access a special variable called self<\/code>. The self<\/code> variable means the current class.<\/p>\n\n\n\n
The following shows how to call a static method from the inside of the class:<\/p>\n\n\n
self<\/span>::staticMethod(arguments);<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
To call a static method from the outside of the class, you use the following syntax:<\/p>\n\n\n
className::staticMethod(arguments<\/span>)<\/code><\/span>Code language:<\/span> JavaScript<\/span> (<\/span>javascript<\/span>)<\/span><\/small><\/pre>\n\n\n
For example:<\/p>\n\n\n
MyClass<\/span>::staticMethod()<\/span><\/code><\/span>Code language:<\/span> CSS<\/span> (<\/span>css<\/span>)<\/span><\/small><\/pre>\n\n\n
The following example defines the HttpRequest<\/code> class that has a static method uri()<\/code> that returns the URI of the current HTTP request:<\/p>\n\n\n
class<\/span> HttpRequest<\/span>\n<\/span>{\n\tpublic<\/span> static<\/span> function<\/span> uri<\/span>()<\/span>: string<\/span>\n\t<\/span>{\n\t\treturn<\/span> strtolower($_SERVER['REQUEST_URI'<\/span>]);\n\t}\n}<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
The following calls the uri()<\/code> static method of HttpRequest<\/code> class:<\/p>\n\n\n
echo<\/span> HttpRequest::uri();<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
If the current HTTP request is https:\/\/phptutorial.net\/php-static-method\/<\/code>, the uri()<\/code> method will return \/php-static-method\/<\/code>.<\/p>\n\n\n\n
Static properties #<\/a><\/h3>\n\n\n\n
To define a static property, you also use the static<\/code> keyword:<\/p>\n\n\n
public<\/span> static<\/span> $staticProperty;<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
For example:<\/p>\n\n\n
class<\/span> MyClass<\/span>\n<\/span>{\n\tpublic<\/span> static<\/span> $staticProperty;\n\n\tpublic<\/span> static<\/span> function<\/span> staticMethod<\/span>()<\/span>\n\t<\/span>{\n\t}\n}<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
To access a public static property outside of the class, you also use the class name with the ::<\/code> operator:<\/p>\n\n\n
MyClass::$staticProperty;<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Like the static methods, to access static properties from within the class, you use the self<\/code> instead of  $this<\/code> as follows:<\/p>\n\n\n
self<\/span>::staticProperty<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
self vs. $this #<\/a><\/h2>\n\n\n\n
The following table illustrates the differences between the self<\/code> and $this<\/code>:<\/p>\n\n\n\n
$this<\/code><\/th>self<\/code><\/th><\/tr><\/thead>
Represents an instance of the class or object<\/td>Represents a class<\/td><\/tr>
Always begin with a dollar ($) sign<\/td>Never begin with a dollar($<\/code>) sign<\/td><\/tr>
Is followed by the object operator (-><\/code>)<\/td>Is followed by the ::<\/code> operator<\/td><\/tr>
The property name after the object operator (-><\/code>) does not have the dollar ($) sign, e.g., $this->property<\/code>.<\/td>The static property name after the ::<\/code> operator always has the dollar ($<\/code>) sign.<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
PHP static methods and properties example #<\/a><\/h2>\n\n\n\n
Suppose that you want to create an App<\/code> class for your web application. And the App<\/code> class should have one and only one instance during the lifecycle of the application. In other words, the App<\/code> should be a singleton.<\/p>\n\n\n\n
The following illustrates how to define the App class by using the static methods and properties:<\/p>\n\n\n
<?php<\/span>\n\nclass<\/span> App<\/span>\n<\/span>{\n\tprivate<\/span> static<\/span> $app = null<\/span>;\n\n\tprivate<\/span> function<\/span> __construct<\/span>()<\/span>\n\t<\/span>{\n\t}\n\n\tpublic<\/span> static<\/span> function<\/span> get<\/span>()<\/span> : App<\/span>\n\t<\/span>{\n\t\tif<\/span> (!self<\/span>::$app) {\n\t\t\tself<\/span>::$app = new<\/span> App();\n\t\t}\n\n\t\treturn<\/span> self<\/span>::$app;\n\t}\n\n\tpublic<\/span> function<\/span> bootstrap<\/span>()<\/span>: void<\/span>\n\t<\/span>{\n\t\techo<\/span> 'App is bootstrapping...'<\/span>;\n\t}\n}<\/span><\/code><\/span>Code language:<\/span> HTML, XML<\/span> (<\/span>xml<\/span>)<\/span><\/small><\/pre>\n\n\n
How it works:<\/p>\n\n\n\n
First, define a static property called $app and initialize its value to null<\/code>:<\/p>\n\n\n
private<\/span> static<\/span> $app = null<\/span>;<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
private<\/span> function<\/span> __construct<\/span>()<\/span>\n<\/span>{\n}<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Third, define a static method called get()<\/code> that returns an instance of the App<\/code> class:<\/p>\n\n\n
public<\/span> static<\/span> function<\/span> get<\/span>()<\/span> : App<\/span>\n<\/span>{\n\tif<\/span> (!self<\/span>::$app) {\n\t\tself<\/span>::$app = new<\/span> App();\n\t}\n\n\treturn<\/span> self<\/span>::$app;\n}<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
The get()<\/code> method creates an instance of the App<\/code> if it has not been created, otherwise, it just simply returns the App’s instance. Notice that the get()<\/code> method uses the self<\/code> to access the $app<\/code> static property.<\/p>\n\n\n\n
Fourth, the bootstrap()<\/code> method is just for demonstration purposes. In practice, you can place the code that bootstraps the application in this method.<\/p>\n\n\n\n
The following shows how to use the App<\/code> class:<\/p>\n\n\n
<?php<\/span>\n\n$app = App::get();\n$app->bootstrap();<\/span><\/code><\/span>Code language:<\/span> HTML, XML<\/span> (<\/span>xml<\/span>)<\/span><\/small><\/pre>\n\n\n
In this code, we called the get()<\/code> static method from the App<\/code> class and invoked the bootstrap()<\/code> method of the App<\/code>‘s instance.<\/p>\n\n\n\n
Summary #<\/a><\/h2>\n\n\n\n
    \n
  • Static methods and properties are bound to a class, not individual objects of the class.<\/li>\n\n\n\n
  • Use the static<\/code> keyword to define static methods and properties.<\/li>\n\n\n\n
  • Use the self<\/code> keyword to access static methods and properties within the class.<\/li>\n<\/ul>\n
    \n\t
    \n\t\t
    Did you find this tutorial useful?<\/div>\n\t\t
    \n\t\t\t\n\t\t\t\t\n\t\t\t\t\t<\/path>\n\t\t\t\t<\/svg>\n\t\t\t\t Yes <\/span>\n\t\t\t<\/button>\n\n\t\t\t\n\t\t\t\t\n\t\t\t\t\t<\/path>\n\t\t\t\t<\/svg>\n\t\t\t\t No <\/span>\n\t\t\t<\/button>\n\t\t<\/div>\n\t<\/header>\n\n\t
    \n\t\t
    \n\t\t\t
    <\/div>\n\t\t\t\n\t\t\t
Try it<\/a><\/p>\n\n\n\n
Second, make the constructor<\/a> private so that the class cannot be instantiated from the outside:<\/p>\n\n\n