Tools like resharper allow you to extract an interface from a class.
At a simple level you can just pull out all the public functions. Happy days, look Ma, I'm programming to an interface.
But what does that really buy you.
Lets say I have my AnalogTemperatureSensor class, and I extract an IAnalogTemperatureSensor interface.
So now I have a function that takes in readings, and gets some form of summary data, say an AverageWithOutliersRemoved .
Then when I want the same functionality for my WaterLevelSensor, I find that it does not share the Functions to choose Centigrade or Fahrenheit.... Opps, I can't reuse my code.
Also, there's no clear way to see what functions from IAnalogTemperatureSensor the AverageWithOutliersRemoved function will use.
IAnalogSensor
On the other hand, If I had simply extracted an IAnalogSensor with functions like TakeReading(), IsReadingValid(), then my AnalogTemperatureSensor and my WaterLevelSensor could both implement this.
AnalogTemperatureSensor might also implement ITemperatureDevice, which allows me to choose C or F.
Several Small Specific interfaces are a whole better than one big nasty one.
