Dependency & association in UML
There two types of relationship between Classes: dependencies and associations.When we talk about one and while we forget another, this is misunderstanding caused by definition of dependency and association.Normally, the definition of those terms are:
Dependency: there are two classes, class A depends on class B. Class B will be affected when class A changed.
Association: An association represents a structural relationship that connects two classes.
the key point: Association imply that there is strong dependency between two classes.In other words, the definition for association should be:
An association represents a structural relationship that connects two classes.class A associate with class B. Class B will be affected when class A changed yet.
In my view, dependency emphasize the needs of on class to another. the association emphasize that structure: one class holds the another, it can use freely when it needs.
Last but not least, a simple demo will told us the truth:
The diagram describe the blow relationships:
class Program
{
class Phone
{
public void SendMessage(string name,string message)
{
Console.WriteLine("Hi,{0}\n{1}",name,message);
}
}
class Employee
{
public void SayHello2Customer()
{
Phone phone = new Phone(); //Dependency, employee needs the phone
phone.SendMessage("Someone", "Hello");
}
}
class Manager
{
Employee staff = new Employee(); //Association, a structure shwos that Manager employeed the staff.
public void SayHello2Customer()
{
staff.SayHello2Customer(); //Manager can employ the staff do something if he want.
}
}
static void Main(string[] args)
{
Manager manager = new Manager();
manager.SayHello2Customer();
Console.ReadKey();
}
}