Throwing exception vs returning null value with switch statement

Question

So I have function that formats a date to coerce to given enum DateType{CURRENT, START, END} what would be the best way to handling return value with cases that use switch statement

public static String format(Date date, DateType datetype) {
    ..validation checks

    switch(datetype){
    case CURRENT:{
        return getFormattedDate(date, "yyyy-MM-dd hh:mm:ss");
    }               
    ... 
     default:throw new ("Something strange happend");
    }

}

OR throw excpetion at the end

   public static String format(Date date, DateType datetype) {
            ..validation checks

            switch(datetype){
            case CURRENT:{
                return getFormattedDate(date, "yyyy-MM-dd hh:mm:ss");
            }               
            ... 
            }

               //It will never reach here, just to make compiler happy 
        throw new IllegalArgumentException("Something strange happend");    
        }

OR return null

public static String format(Date date, DateType datetype) {
            ..validation checks

            switch(datetype){
            case CURRENT:{
                return getFormattedDate(date, "yyyy-MM-dd hh:mm:ss");
            }               
            ... 
            }

             return null;   
}

What would be the best practice here ? Also all the enum values will be handled in the case statement

Answer 1

Throw an exception, since this is an exceptional case.

And throw it outside the switch, it would be more readable. Otherwise it sounds like "the default case is exceptional".

Answer 2

I would go with the first approach (but with IllegalArgumentException as in your second approach). You should include a default statement to guard against cases when someone modifys (extends) your enum. Putting the exception in the default-statement makes clear to the reader that the code is never supposed to get past the switch-statement. Otherwise they would have to check if really all of the enum values are in the switch.

Answer 3

Exceptions, as you can obey more to the parent than a single return int can. Usually you use Exceptions where they exist (C++), and return values where not (C).

Answer 4

I think that throw new IllegalArgumentException("Something strange happend") is the best pratice.

Using null will just presumibly cause a NullPointerException somewhere when you use the return value but it will be less informative than raising a specific exception that describes the problem!

And you know: clear errors = better developing.