Should you avoid Guavas Ordering.usingToString()?

Question

This question was prompted after reading Joshua Bloch's "Effective Java". Specifically in Item #10, he argues that it is bad practice to parse an object's string representation and use it for anything except a friendlier printout/debug. The reason is that such a use "is error-prone, results in fragile systems that break if you change the format". To me it looks like Guava's Ordering.usingToString() is a spot on example of this. So is it bad practice to use it?

Answer 1

Well, if the sorting is only used for deciding in which order to display things to a user, I'd argue it's part of "friendlier printout/debug".

If, however, your codes correctness depends on the ordering, then I'd argue that it's indeed a bad idea to depend on toString.

Answer 2

As the author of that method, I would agree: it's really just a crutch. For those "look, I just need an Ordering<Object>, dammit" cases. It should probably be removed, since you can get its behavior with Ordering.onResultOf(Functions.toStringFunction) anyway.

Answer 3

If your program ever used the toString() for lexical sorting using natural ordering in such a way that program execution depends on it, then it would be wise to override the default toString() of the class that extended. You should in that case make the toString() method final and clearly document that it is used for ordering.

It would however be much better to create another method returning a String and create an ordering depending on that result, possibly by creating a specific Comparator to do the sorting. See for instance the final method name() used for enumerations in Java. In general it creates the same String as toString() but it is still possible to perform ordering with it even if toString() has been overridden.

If you use the last method, then the Ordering.usingToString() would not be of much use of course.

Answer 4

There are some obvious cases where it actually makes sense like StringBuffer etc. Obviously it doesn't make sense for most "business" classes to depend on toString().