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:

 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
 }

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.

[NogDog]

Most typical would be to pass an object to another object when it needs to have access to it.

class Class_B
{
   private $a;
   public __construct(Class_A $a)
   {
      $this->a = $a;
   }
   public function example()
   {
      $this->a->some_method_from_Class_A();
   }
}

$obj_a = new Class_A();
$obj_b = new Class_B($obj_a);

For more complex inter-object communication, you might want to look into the registry pattern.

[PHPycho]

Thanks Mr. NogDog
I think i should go for registry pattern right

[PHPycho]

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

[NogDog]

It's not really possible to provide a specific solution without understanding the specific situation. Generally speaking, a major design goal should be to keep each class as independent as possible. When you start using something like the Registry pattern, you start adding a sort of system-wide constraint somewhat analogous to using global variables (though not that bad). Realistically, though, as a system reaches some level of size and complexity, the benefits of such an implementation (using some sort of global object like a Registry object) may well out-weigh the closer coupling it begins to impose on your application. You'll need to make the judgment based on your particular application design whether it makes more sense to use a Registry object or to simply pass object references to other objects as needed (or very likely some of each).

PS: Depending upon what you mean by "communicate", it may be that in some cases you are looking more at some sort of composition pattern, where Class A internally creates its own instance of Class B, for example. Again, it all depends on the specific application design and the context and purpose of those object relationships.