PHP中的OOP可见性

Question

I have recently started OOP in PHP and I am on visibility concept (public, protected, private). Here I'm confused about protected visibility. Protected members can only be accessible within the declaring clas or a subclass or child class. I have this example on PHP's site:

class MyClass
{
    public $public = 'Public';
    protected $protected = 'Protected';
    private $private = 'Private';

    function printHello()
    {
        echo $this->public;
        echo $this->protected;
        echo $this->private;
    }
}


class MyClass2 extends MyClass
{
    // We can redeclare the public and protected method, but not private
    protected $protected = 'Protected2';

    function printHello()
    {
        echo $this->public;
        echo $this->protected;
        echo $this->private;
    }
}

$obj2 = new MyClass2();
echo $obj2->public; // Works
echo $obj2->protected; // Fatal Error
echo $obj2->private; // Undefined
$obj2->printHello(); // Shows Public, Protected2, Undefined

In this code in the third last line (echo $obj2->protected; // Fatal Error) it gives fatal error. But isn't protected variable inherited into child class which is MyClass2 in this case? So why this fatal error? Can someone please enlighten me about this?

Answer 1

Protected members can only be accessible within the declaring class or a subclass or child class.

You must pay attention to the within.

You're getting the fatal error because you're accessing $protected from outside both MyClass2 and MyClass.

Within means that you can access it from MyClass2 like you're doing on MyClass2::printHello() and/or MyClass::printHello() methods.