Interfaces - Illustrated C# 2005 - page 374

So how can you make the Sort method work with objects of type MyClass ? To implement
an interface, a class or struct must do two things:

￿ It must list the interface name in its base class list.

￿ It must provide an implementation for each of the interface's members.

For example, the following code updates MyClass to implement interface IComparable .
Notice the following about the code:

￿ The name of the interface is listed in the base class list of the class declaration.

The class implements a method called CompareTo , whose parameter type and return type
match those of the interface member.

￿

￿Method CompareTo is implemented following the definition given in the interface's doc-
umentation. That is, it returns a negative 1, positive 1, or 0, depending on its value
compared to the object passed into the method.

Interface name in base class list
↓
class MyClass : IComparable
{
public int TheValue;

public int CompareTo(object obj) // Implementation of interface method
{
MyClass mc = (MyClass)obj;
if (this.TheValue < mc.TheValue) return -1;
if (this.TheValue > mc.TheValue) return 1;
return 0;
}
}

Figure 17-2 illustrates the updated class. The arrow from the grayed interface method
to the class method indicates that the interface method does not contain code, but is imple-
mented by the class-level method.

Figure 17-2. Implementing IComparable in MyClass