Difficulty understanding how to declare a parent class's function in an extended class?

Question

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

    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();
//Foo::testPublic
//Bar::testPrivate

I'm having a lot of trouble understanding this output. Would someone be able to give me a clear succinct explanation of what is going on? I'm learning OOP and wanted to know how to use extensions to override the parent class functions.

zerkms · Accepted Answer · 2013-01-16 20:26:40Z

5

The test() method calls 2 methods:

testPublic - it's a public one, so it was overriden in the Foo. So the Foo::testPublic is called
testPrivate - it's a private one, so it's only visible for each class itself. For the caller method (it's Bar) - it's a Bar::testPrivate

So - if the method is public or protected - it can be overriden and called from the ancestor/child; if it's private - it cannot.

answered Jan 16, 2013 at 20:26

zerkms

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Reactgular · Accepted Answer · 2013-01-16 20:33:52Z

The $this references the current object. So when you do the following.

$this->testPublic();

It will call testPublic() for the top most class that implements that function.

If you want to only call the parent class, then there is the parent keyword.

parent::testPublic();

That will call testPublic() on the class below the current object.

Becare full not to confuse the -> operator with the :: operator.

The :: operator references the class definition of an object, where as -> references the instance of an object.

 self::testPublic();
 $foo::testPublic();

That references a static function called testPublic(), and static methods are defined at the class level.

 $foo->testPublic();
 $this->testPublic();

That references a function as part of the instance of an object, and there is a vtable used to look up which object instance level should be called.

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