Static Classes can be transformed into Singleton Objects.
Singleton Objects support interfaces.
Interfaces can be used for different implementations.
(1) Definition of Problem.
Suppose you have a class that have static members.
--
StringsClass.cs
--
namespace Libraries
{
public static class StringsClass
{
public static string UppercaseCopy(string Value)
{
string Result = "";
// code where "Value" is converted to uppercase,
// and output stored in "Result"
return Result;
} // string UppercaseCopy(...)
public static string LowercaseCopy(string Value)
{
string Result = "";
// code where "Value" is converted to lowercase,
// and output stored in "Result"
return Result;
} // string LowercaseCopy(...)
public static string ReverseCopy(string Value)
{
string Result = "";
// code where "Value" is reversed,
// and output stored in "Result"
return Result;
} // string ReverseCopy(...)
} // class StringsClass
} // namespace Libraries
--
And, several code that uses that static elements, from that class.
--
StringsLibraryUser.cs
--
using Libraries;
namespace MyApp
{
public class AnyClass
{
public void AnyMethod()
{
string Example = "HELLO EARTH";
string AnotherExample = StringsClass.LowercaseCopy(Example);
} // void AnyMethod(...)
} // class AnyClass
} // namespace MyApp
--
(2) Transform, first, the class, into a non static class.
--
StringsClass.cs
--
namespace Libraries
{
public class StringsClass
{
public string UppercaseCopy(string Value)
{
string Result = "";
// code where "Value" is converted to uppercase,
// and output stored in "Result"
return Result;
} // string UppercaseCopy(...)
public string LowercaseCopy(string Value)
{
string Result = "";
// code where "Value" is converted to lowercase,
// and output stored in "Result"
return Result;
} // string LowercaseCopy(...)
public string ReverseCopy(string Value)
{
string Result = "";
// code where "Value" is reversed,
// and output stored in "Result"
return Result;
} // string ReverseCopy(...)
} // class StringsClass
} // namespace Libraries
--
(3) Add code the allow class handle a single object.
--
StringsClass.cs
--
namespace Libraries
{
public class StringsClass
{
private static Singleton instance = null;
private Singleton()
{
// ...
}
public static synchronized Singleton getInstance()
{
if (instance == null) {
instance = new Singleton();
}
return instance;
}
public string UppercaseCopy(string Value)
{
string Result = "";
// code where "Value" is converted to uppercase,
// and output stored in "Result"
return Result;
} // string UppercaseCopy(...)
public string LowercaseCopy(string Value)
{
string Result = "";
// code where "Value" is converted to lowercase,
// and output stored in "Result"
return Result;
} // string LowercaseCopy(...)
public string ReverseCopy(string Value)
{
string Result = "";
// code where "Value" is reversed,
// and output stored in "Result"
return Result;
} // string ReverseCopy(...)
} // class StringsClass
} // namespace Libraries
--
(4) Code that calls the class, should add the reference for the singleton.
--
StringsLibraryUser.cs
--
using Libraries;
namespace MyApp
{
public class AnyClass
{
public void AnyMethod()
{
string Example = "HELLO EARTH";
string AnotherExample = StringsClass.getInstance().LowercaseCopy(Example);
} // void AnyMethod(...)
} // class AnyClass
} // namespace MyApp
--
(5) Define an interface, with similar declarations to the previous static class,
and allow the singleton, to implement that interface. Omit the singletons members, in the interface declaration
--
StringsClass.cs
--
namespace Libraries
{
public interface StringsInterface
{
string UppercaseCopy(string Value);
string LowercaseCopy(string Value);
string ReverseCopy(string Value);
} // interface StringsInterface
public class StringsClass: StringsInterface
{
private static Singleton instance = null;
private Singleton()
{
// ...
}
public static synchronized Singleton getInstance()
{
if (instance == null) {
instance = new Singleton();
}
return instance;
}
public string UppercaseCopy(string Value)
{
string Result = "";
// code where "Value" is converted to uppercase,
// and output stored in "Result"
return Result;
} // string UppercaseCopy(...)
public string LowercaseCopy(string Value)
{
string Result = "";
// code where "Value" is converted to lowercase,
// and output stored in "Result"
return Result;
} // string LowercaseCopy(...)
public string ReverseCopy(string Value)
{
string Result = "";
// code where "Value" is reversed,
// and output stored in "Result"
return Result;
} // string ReverseCopy(...)
} // class StringsClass
} // namespace Libraries
--
(6) In the code, where your are using your singleton, the previous class that contained static methods, replace the singleton for an interface.
--
StringsLibraryUser.cs
--
using Libraries;
namespace MyApp
{
public class AnyClass
{
public StringsInterface StringsHelper = StringsClass.getInstance().LowercaseCopy(Example);
public void AnyMethod()
{
string Example = "HELLO EARTH";
string AnotherExample = StringsHelper;
} // void AnyMethod(...)
} // class AnyClass
} // namespace MyApp
--
Now, you can add other classes that support the same declarations,
with different implementation.
Cheers.
--
