Question

What’s the best practise when adapting C-style functions which return a true/false to Java?

Here’s a simple method to illustrate where the problem lies.

public static boolean fileNameEndsWithExtension( String filename, String fileExtension)  { 
    return filename.endsWith( fileExtension );
}

Note that there’s probably a more elegant way of filtering files (feel free to comment on this). Anyway, if filename is a null value, does one:

1. Return a false if filename is null? If so, how does one go about distinguishing between the case where filename is null and the case where the String or file name doesn’t end with a given file extension?
2. Change the return type to the wrapper class Boolean which allows a null value.
3. Throw an Exception and force the programmer to make sure that a null value is never passed to the method?
4. Use another solution?

Answer 1

You should throw a NullPointerException or an IllegalArgumentException if filename is null. I’ll let you decide which is best. There’s a good debate on which to use in the question: IllegalArgumentException or NullPointerException for a null parameter?