Regex or Exception Handling?

Question

Which one of the following is a better practice to check if a string is float?

try{
 Double.parseDouble(strVal);
}catch(NumberFormatException e){
 //My Logic         


        

Answer 1

The first one is going to perform better than the regex when the string matches the double. For one it's very fast to parse it when the recognizer is hard coded as it would be with Double.parse. Also there's nothing to maintain it's whatever Java defines as the Double is as a string. Not to mention Double.parseDouble() is easier to read.

The other solution isn't going to be compiled so the first thing that the regex has to do is compile and parse the regex expression, then it has to run that expression, then you'll have to execute Double.parseDouble() to get it into a double. And that's going to be done for every number passed to it. You might be able to optimize it with Pattern.compile(), but executing the expression is going to be slower. Especially when you have to run a Double.doubleParse to get the value into a double.

Yes exceptions are not super fast, but you'll only have to pay that price when you parse an error. If you don't plan on seeing lots of errors then I don't think you'll notice the slow down from gathering the stacktrace on the throw (which is why exceptions perform poorly). If you're only going to encounter a handful of exceptions then performance isn't going be a problem. The problem is you expected a double and it wasn't so probably some configuration mistake so tell the user and quit, or pick a suitable default and continue. That's all you can do in those cases.