PHP Strict Standards: Declaration of should be compatible

Question

I have the following hierarchy of classes:

class O_Base {...}

class O extends O_Base {...}

abstract class A_Abstract {
    public function save(O_Base $obj) {         


        

Answer 1

Do you see the difference of the function signatures?

// A_Abstract
public function save(O_Base $obj) {...}

// A
public function save(O $obj) {

They are not compatible.