PHP Static Methods and Properties

There are two types of class members in PHP.

Static Members
Instance Members

The main differences are :

Static Member	Instance Member
It accessed by class name	It accessed by object name
It shares a common memory for all objects.	It creates new memory for every objects.
It is not depends to object.	It is depends to object.
It create memory only once in their life.	It create memory whenever a new object is created.
Instances of a class do not need to be created in order to call static methods and properties directly.	We must create a object of a class in order to call instance members.

Syntax :- The static keyword is used to declare static methods and properties..

<?php
class MyClass {

  public static $staticVariable;

  public static function staticMethod() {
    echo "Hello World!";
  }
}
?>

Syntax :- Accessing a static methods and properties:

//  For Static Property

ClassName::staticPropertyName;

//  For Static Method

ClassName::staticMethodName();

Example 1 :- The following example contains a static property and method.

<?php
class MyClass {

  //    A static property

  public static $name = "ABC";

  //    A static method

  public static function sayHello() {
    echo "Hello";
  }
}

//  Call static property

echo MyClass::$name;

echo "<br />";

//  Call static method

MyClass::sayHello();
?>

Output :-

ABC
Hello

Example 2 :- The following example display difference between static members and instance members.

<?php
class MyClass {
  //    A static property

  public static $x = 10;

  //    A instance property

  public $y = 10;

  function showXY()
  {
	echo "X = " . MyClass::$x . " , Y = " . $this->y . "<br />";
	MyClass::$x += 1;
	$this->y += 1;
  }
}

$obj1 = new MyClass();
$obj2 = new MyClass();
$obj3 = new MyClass();

$obj1->showXY();
$obj2->showXY();
$obj3->showXY();

$total = MyClass::$x + $obj1->y + $obj2->y + $obj3->y;
echo "<br /><br />The total is : " . $total;
?>

Output :-

X = 10 , Y = 10
X = 11 , Y = 10
X = 12 , Y = 10

The total is : 46

Note:- Static and non-static methods are both possible in a same class.

Use the self keyword followed by a double colon (::) to access a static method from a method in the same class.

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