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The static Keyword and Constants

A constant, value of which does not change, can be declared for a class. It can be overridden in the child class. A static property or method can be accessed without any instantiation of the class. While a class constant can only be public, a static property can be protected or private. A constant or a static member can be accessed with ::.
Only constants and static members may be accessed without any instantiation. They must be accessed with ::, with the exeception of
$obj->static_func(). parent:: and self:: refer to the parent class and current class respectively. $this must not be used in a static method.
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class P{
   const c=1;
   static private $v1=2;
   static $v2=3;
   public $v3=4;
   static function f(){
      echo self::$v1;
      //echo $this->v3=1;  //error
   }
   function g(){
      echo 5;
   }
}
class C extends P{
   static function f(){  // method overriding
      echo parent::c;
      echo self::c;   // also visible
   }
}
echo P::c;         //1
echo P::$v2;     //3
P::f();              //2
C::f();              //11
$s="P";$s::f(); //2
$s="f";P::$s(); //2
$a=new P;
echo $a::c;       //1
echo $a::$v2;   //3
$a::f();             //2
$a->f();            //2
//P::g();           // 5, warning
//$a::g();         // 5, warning
//echo $a->c;   // error
//echo $a->$v2;// error
//echo $a::$v3; // error
//echo P::$v3;   // error
//P->f();           // error
//P->c1;            // error
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An object can be created out of a static function.
Only constants and static members may be accessed without any instantiation. They must be accessed with ::, with the exeception of
$obj->static_func(). parent:: and self:: refer to the parent class and current class respectively. $this must not be used in a static method.
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class C{
   static function getNew(){
      return new static;
   }
}
$a=C::getNew();
var_dump($a instanceof C);
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Late static binding can be achieved with static::. It allows an overriding member to be chosen, when the member is used from the base class.
Only constants and static members may be accessed without any instantiation. They must be accessed with ::, with the exeception of
$obj->static_func(). parent:: and self:: refer to the parent class and current class respectively. $this must not be used in a static method.
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<body><?php
class P1 {
   public static function which() {
      echo __CLASS__;
   }
   public static function test() {
       self::which();     //P1
       static::which();  //C1
       P1::which();      //P1
       C1::which();      //C1
   }
}
class C1 extends P1 {
    public static function which() {  // overriding method
        echo __CLASS__;
    }
}
C1::test();

class P2 {
   private function which() {
      echo __CLASS__;
   }
   public function test() {
       $this->which(); //P2
       self::which();    //C2
   }
}
class C2 extends P2 {
    public function which() {
        echo __CLASS__;        
    }
}
$v2=new C2;
$v2->test();
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