PHP manual OOP visibility example - can someone explain it

Question

I saw this in the PHP OOP manual http://www.php.net/manual/en/language.oop5.visibility.php and I can't get my head around why the output is not: Foo::testPrivate Foo::testPublic

class Bar 
{
    public function test() {
        $this->testPrivate();
        $this->testPublic();
    }

    public function testPublic() {
        echo "Bar::testPublic\n";
    }

    private function testPrivate() {
        echo "Bar::testPrivate\n";
    }
}

class Foo extends Bar 
{
    public function testPublic() {
        echo "Foo::testPublic\n";
    }

    private function testPrivate() {
        echo "Foo::testPrivate\n";
    }
}

$myFoo = new foo();
$myFoo->test(); // Bar::testPrivate 
                // Foo::testPublic

Answer 1

It's all about the visibility of the variables / methods.

You'll notice that in the Bar class, the method testPrivate() is private. That means that ONLY itself can access that method. No children.

So when Foo extends Bar, and then asks to run the test() method, it does two things:

1. It overrides the testPublic() method because it's public, and Foo has the right to override it with it's own version.
2. It calls test() on Bar (since test() only exists on Bar()).

testPrivate() is not overridden, and is part of the class that holds test(). Therefore, Bar::testPrivate is printed.
testPublic() is overridden, and is part of the inheriting class. Therefore, Foo::testPublic is printed.

Answer 2

In some cases, it is easy to notice that you want a private method on the Bar class, but you also wants the Foo class to access it.
But wait, it is public or private?
Here comes the protected modifier.
When a method is private, only the class itself can call the method.
When a method is public, everyone can call it, like a free party.
When a method is protected, the class itself can call it and also whoever inhered this method (children) will be able to call it as a method of their own.