communication between classes ?

[PHPycho]

Hello forums!
One thing always comes on my mind while coding in OOP is that 'communication between classes'
I am searching for a effective communication mechanism between different classes in a OOP sytem.

Cases:
[PHP] class A{
//what should be the rule when it requires to communicate with B, C & D classes
}

class B{
//what should be the rule when it requires to communicate with D classes
}

class C{
// any other...
}

class D{
// what should be the rule if it requires to communicate with C class
}[/PHP]
Above is just the case of communication between different classes.

Can anybody point the good communication mechanism between different classes.

Thanks in advance for the valueable help.

[xiongbin]

can use extends

[PHPycho]

but its not effective to extend for unsimilar classes isnt it ?

[PHPycho]

What about registry pattern for holding and using objects in this case or else methods ?

[mehh]

I'm not sure if this is what you need but you could use this

class A{
 }
class B{
 var $A=null;
 function B(){
  $this->A=new A();
  }
 }

Also you may be able to do something with call_user_func_array [php.net] and func_get_args [uk2.php.net] so the arguments for the constructer are automaticly passed