| Class | Package | Subclass | Subclass | World
            |       |         |(same pkg)|(diff pkg)| 
————————————+———————+—————————+——————————+——————————+————————
public      |   +   |    +    |    +     |     +    |   +     
————————————+———————+—————————+——————————+——————————+————————
protected   |   +   |    +    |    +     |     +    |   o     
————————————+———————+—————————+——————————+——————————+————————
no modifier |   +   |    +    |    +     |     o    |   o
————————————+———————+—————————+——————————+——————————+————————
private     |   +   |    o    |    o     |     o    |   o

+ : accessible
o : not accessible

source : http://stackoverflow.com/questions/215497/in-java-difference-between-default-public-protected-and-private

// Public
public $variable;
public function doSomething() {
  // ...
}

// Private
private $variable;
private function doSomething() {
  // ...
}

// Protected
protected $variable;
protected function doSomething() {
  // ...
}

• public scope to make that variable/function available from anywhere, other classes and instances of the object.
• private scope when you want your variable/function to be visible in its own class only.
• protected scope when you want to make your variable/function visible in all classes that extend current class including the parent class.

• http://php.net/manual/en/language.oop5.visibility.php