replaceexceptionwithconditional

Today's refactoring doesn't come from any place specifically, just something I've picked up over time that I find myself using often. Any variations/comments would be appreciated to this approach. I think there's some other good refactorings around these type of problems. A common code smell that I come across from time to time is using exceptions to control program flow. You may see something to this effect:

public interface MicrowaveMotor {
	public void cook(String dish);
}

public class InUseException extends RuntimeException{

	private static final long serialVersionUID = -7115741647066213175L;
	public InUseException(String message){
		super(message);
	}
}

public class Microwave {
	private MicrowaveMotor motor;
	public boolean cook(String dish){
		boolean cooked = false;
		try{
			motor.cook(dish);
			cooked = true;
		}
		catch(InUseException e){
			cooked = false;
		}
		return cooked;
	}
}

Exceptions should only be there to do exactly what they are for, handle exceptional behavior. Most of the time you can replace this type of code with a proper conditional and handle it properly. This is called design by contract in the after example because we are ensuring a specific state of the Motor class before performing the necessary work instead of letting an exception handle it.

public interface MicrowaveMotor {
	public void cook(String dish);
	public boolean inUse();
}

public class Microwave {
	private MicrowaveMotor motor;

	public boolean cook(String dish) {
		if (motor.inUse())
			return false;
		else
			motor.cook(dish);
		return true;
	}
}

##Original C# Code from the book:

public class Microwave {
   private IMicrowaveMotor Motor { get; set;}
   public bool Start(object food) {
		bool foodCooked = false;
		try{
 			Motor.Cook(food);
 			foodCooked = true;
 		}
 		catch(InUseException){
 			foodcooked = false;
 		}
 		return foodCooked;
 	}
}

public class Microwave {
   private IMicrowaveMotor Motor { get; set; }
   public bool Start(object food) {
		if (Motor.IsInUse)
			return false;

 		Motor.Cook(food);
 		return true;
 	}
}