minte9
LearnRemember / PHP



Resource

Public - accesed from any scope Protected - from within the class and its descendants Private - from within the class only Final - from any scope, but cannot be overriden in descendants 
 
class A 
{
    public $a;
    protected $b;
    private $c;

    public $d = "Test"; // String
    public $e = 1.23; // Numeric value
    public $f = array (1, 2, 3);
}

$obj = new A();

$obj->a = 1;
$obj->c = 3; // Error:  Cannot access private property

Final

Final visibility applies to methods and classes only. Final method cannot be overidden. Final class cannot be extended. 
 
final class A
{
    final $c = 0; 
        // Error: final modifier is allowed ...
        // only for methods and classes

    final public function sum($a, $b) {
        return $a + $b;
    }
}

Constructors

Constructors are normaly declared public. Constructors are private in patterns like Singleton. You can't initialize a variable by calling a function. That is done in constructor. 
 
class A
{
    public $a = init(); // Error: Invalid operations

    public function init() {}
}

Static

Static methods or properties can be access only as part of a class itself. This allows true encapsulation and avoid naming conflicts. Accessing static with -> generates notice. 
 
error_reporting(E_ALL);

class A
{
    public static $to = "World";

    public static function bar()
    {
        echo "Hello " . self::$to;
    }
}

echo A::$to; // World

$obj = new A();
$obj->bar(); // Hello World

echo $obj->to; // Accessing static property A::$to as non static






Questions and answers




Protected property can be accessed only from the ...

  • a) current class
  • b) current class and its descendants

Final property applies to:

  • a) classes and methods
  • b) classes, methods and properties

A class constant cannot be declared final.

  • a) false
  • b) true

Static properties are accesible as part of the:

  • a) class
  • b) instance

How do you call a constant "TO" from a class foo?

  • a) foo::$TO
  • b) foo::TO

How do you call static property "to" from a class "foo"?

  • a) foo::$to
  • b) foo::to


References