Zend PHP 7 Certification – OOP – Static Methods and Properties

8th September 2017

This post covers the Static Methods and Properties section of the OOP chapter when studying for the Zend PHP 7 Certification.

Declaring class properties or methods as static, using the static keyword, makes them accessible without needing an instantiation of the class.

A property declared as static cannot be accessed with an instantiated class object (though a static method can).

<?php
class MyClass {
    public static $someVar = 'Some property';

    public static function someMethod()
    {
        return __FUNCTION__;
    }
}

echo MyClass::$someVar;      // Outputs: Some property
echo MyClass::someMethod();  // Outputs: someMethod

<?php
class MyClass {
    public static $someVar = 'Some property';

    public static function someMethod()
    {
        return __FUNCTION__;
    }
}

echo MyClass::$someVar;      // Outputs: Some property
echo MyClass::someMethod();  // Outputs: someMethod

$myClass = new MyClass();
echo $myClass->someVar;      // Generates an E_DEPRECATED warning (Property declared as static)
echo $myClass->someMethod(); // Outputs: someMethod

In PHP 7, as seen above, calling non-static methods statically is deprecated, and will generate an E_DEPRECATED warning. Be aware of this as current support for this may be removed in future.

Similarly to non-static properties and methods, if no visibility declaration is used, then the properties and methods are treated as public.

It is possible to reference the class using a variable.

<?php
class MyClass {
    public static $someVar = 'Some property';

    public static function someMethod()
    {
        return __FUNCTION__;
    }
}

$className = 'MyClass';
echo $className::$someVar;     // Outputs: Some property
echo $className::someMethod(); // Outputs: someMethod

The self keyword is used to access properties and methods from inside the class definition. self refers to the current class.

<?php
class MyClass {
    public static $someVar = 'Some property';

    public static function someMethod()
    {
        echo self::$someVar . "\n";
        echo self::someOtherMethod();
    }

    public static function someOtherMethod() {
        return __FUNCTION__;
    }
}

MyClass::someMethod();

// Outputs:
Some property
someOtherMethod

Note that because classes do not have be instantiated for access to static properties and methods, attempting to use the $this pseudo-variable will result in a fatal error.

<?php
class MyClass {
    public static $someVar = 'Some property';

    public static function someMethod()
    {
        echo self::$someVar;
        echo $this->someOtherMethod(); // Fatal error
    }

    public static function someOtherMethod() {
        return __FUNCTION__;
    }
}

MyClass::someMethod();

The parent keyword refers to the parent of the current class.

<?php
class OtherClass extends MyClass
{
    public static function someChildMethod() {
        echo parent::someMethod();
    }
}

There have been questions raised by developers about when to use static methods, and what benefit they have over non-static methods.

Static methods are perfectly acceptable to use when you’re defining methods that act in a stateless manner and are predictable.

Examples of static methods could include simple mathematical calculations for testing purposes. Logging classes and needing to output log messages to a file could be another reason to use static methods. Ut is easier to just write Logger::log() for example, rather than instantiate a new class of Logger each time.

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Note: This article is based on PHP version 7.0.