You can use an abstract class like this too:
abstract class A{
public function show(){
echo 'A';
}
}
class B extends A{
public function hello(){
echo 'B';
parent::show();
}
}
$obj = new B;
$obj->hello(); // BA
# See that the abstract class does not have at least one abstract method
# Even in this case, I'm still able to extend it, or call its non-abstract member