Refactoring a Switch Statement

Introduction

This article describes refactoring a switch statement in order to reduce Cyclomatic complexity.

Background

Many developers would have scratched their heads in order to keeptheir Cyclomatic complexity under 10. In some cases, it is really notpossible at first site. In this article, I have provided a way to dothat. Take the example of a Device State machine. You have a number ofdevice states as below:

public enum DeviceStatesEnum
{
    PowerUp,
    Waiting,
    StandBy,
    Inactive,
    Active,
    Start,
    Ready,
    Equilibrating,
    StartRunning,
    Running,
    ShoutingDown,
    ShoutDown,
    WarmingUp,
    Error
}

Using the code

Just download the code and run it.

public enum DeviceStatesEnum
{
    PowerUp,
    Waiting,
    StandBy,
    Inactive,
    Active,
    Start,
    Ready,
    Equilibrating,
    StartRunning,
    Running,
    ShoutingDown,
    ShoutDown,
    WarmingUp,
    Error
}

You have come up with the following class in order to handle the various states:

public class DeviceController
{
   private DeviceStatesEnum _currentDeviceState = DeviceStatesEnum.ShoutDown;

   public void ChangeDeviceState(DeviceStatesEnum deviceState)
   {
       switch (deviceState)
       {
           case DeviceStatesEnum.Active:
                SetDeviceStateToActive();
                break;
           case DeviceStatesEnum.Equilibrating:
                SetDeviceStateToEquilibrating();
                break;
           case DeviceStatesEnum.Error:
                SetDeviceStateToError();
                break;
           case DeviceStatesEnum.Inactive:
                SetDeviceStateToInactive();
                break;
           case DeviceStatesEnum.PowerUp:
                SetDeviceStateToPowerUp();
                break;
           case DeviceStatesEnum.Ready:
                SetDeviceStateToReady();
                break;
           case DeviceStatesEnum.Running:
                SetDeviceStateToRunning();
                break;
           case DeviceStatesEnum.ShoutDown:
                SetDeviceStateToShoutDown();
                break;
           case DeviceStatesEnum.ShoutingDown:
                SetDeviceStateToShoutingDown();
                break;
           case DeviceStatesEnum.StartRunning:
                SetDeviceStateToStartRunning();
                break;
       }
   }

   public DeviceStatesEnum GetDeviceState()
   {
       return _currentDeviceState;
   }

   private void SetDeviceStateToStartRunning()
   {
       if(_currentDeviceState == DeviceStatesEnum.Ready)
       _currentDeviceState = DeviceStatesEnum.StartRunning;
   }

   private void SetDeviceStateToShoutingDown()
   {
       _currentDeviceState = DeviceStatesEnum.ShoutingDown;
   }

   private void SetDeviceStateToShoutDown()
   {
       _currentDeviceState = DeviceStatesEnum.ShoutDown;
   }

   private void SetDeviceStateToRunning()
   {
       if (_currentDeviceState == DeviceStatesEnum.StartRunning )
       {
           _currentDeviceState = DeviceStatesEnum.Running;
       }
   }

   private void SetDeviceStateToReady()
   {
       if (_currentDeviceState == DeviceStatesEnum.Equilibrating )
       {
           _currentDeviceState = DeviceStatesEnum.Ready;
       }
   }

   private void SetDeviceStateToPowerUp()
   {
       if (_currentDeviceState != DeviceStatesEnum.Error)
           _currentDeviceState = DeviceStatesEnum.PowerUp;
   }

   private void SetDeviceStateToInactive()
   {
       if(_currentDeviceState != DeviceStatesEnum.Error)
       _currentDeviceState = DeviceStatesEnum.Inactive;
   }

   private void SetDeviceStateToError()
   {
       _currentDeviceState = DeviceStatesEnum.Error;
   }

   private void SetDeviceStateToEquilibrating()
   {
       if (_currentDeviceState == DeviceStatesEnum.Active)
       {
           _currentDeviceState = DeviceStatesEnum.Equilibrating;
       }
   }

   private void SetDeviceStateToActive()
   {
       if (_currentDeviceState != DeviceStatesEnum.Error)
       {
           _currentDeviceState = DeviceStatesEnum.Active;
       }
   }
}

Since you have 14 states, you will end up having a Cyclomaticcomplexity more than 14. Here is the way to reduce this complexity to1. Do the following changes in the above class DeviceController. Declare a Dictionary.

private Dictionary<DeviceStatesEnum, Action> _deviceStateHandler = 
                                new Dictionary<DeviceStatesEnum, Action>();

Add a constructor to create a mapping with the states.

public DeviceController()
{
   _deviceStateHandler.Add(DeviceStatesEnum.Active, new Action(SetDeviceStateToActive));
   _deviceStateHandler.Add(DeviceStatesEnum.Equilibrating, 
                           new Action(SetDeviceStateToEquilibrating));
   _deviceStateHandler.Add(DeviceStatesEnum.Error, new Action(SetDeviceStateToError));
   _deviceStateHandler.Add(DeviceStatesEnum.Inactive, 
                           new Action(SetDeviceStateToInactive));
   _deviceStateHandler.Add(DeviceStatesEnum.PowerUp, new Action(SetDeviceStateToPowerUp));
   _deviceStateHandler.Add(DeviceStatesEnum.Ready, new Action(SetDeviceStateToReady));
   _deviceStateHandler.Add(DeviceStatesEnum.Running, new Action(SetDeviceStateToRunning));
   _deviceStateHandler.Add(DeviceStatesEnum.ShoutDown, 
                           new Action(SetDeviceStateToShoutDown));
   _deviceStateHandler.Add(DeviceStatesEnum.ShoutingDown, 
                           new Action(SetDeviceStateToShoutingDown));
   _deviceStateHandler.Add(DeviceStatesEnum.StartRunning, 
                           new Action(SetDeviceStateToActive));
   
   //TODO
   //Create mapping for all the states
}

Then, change the ChangeDeviceState as below:

public void ChangeDeviceState(DeviceStatesEnum deviceState)
{
   _deviceStateHandler[deviceState].Invoke();
}

Now the Cyclomatic complexity of the method ChangeDeviceState is one.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

About the Author

rajeshjj