How fast is string.format

Therefore, this library has been built to facilitate fast string formatting capable of formatting logs lines at speed. There are of course already string formatting options in C. Format is great but it's slow and not easy to understand if given only the format string with no parameters. String interpolation is wonderful to read and performs well but it's unfortunately limited to compile time configuration.

Fast String Format is designed to give similar readability and performance as String Interpolation but with a similar runtime flexibility as string. When that Func is run, the entire string operation happens using calls to the very fast string. Concat method. Fast String Format is currently benchmarked against a number of different string formatting methods using BenchmarkNet. FastStringFormat is available as a NuGet package!

Of course, this example is trivial. Since the parsing is entirely within the Compile method, the real power of Fast String Format is found when a single format string needs to be applied to thousands of different data objects.

By default the DefaultFormatParser is used which currently provides similar functionality to String Interpolation. Skip to content. It seemed like a waste of time when I started.

After all, the benchmarks were already done. Why run them again? For one, the machine that we had originally used was decommissioned, and I wanted to see consistent results throughout the talk by running everything on my performance testing machine. For another, I wanted to see whether there were any changes in the JVM that would affect the results. I did not expect the latter to be a factor. Imagine my surprise when I noticed that the String. Or seen from another perspective, Java 17 String.

This is excellent news, but under what circumstances is it faster? Claes was kind enough to respond to my query and confirmed that we can expect the formatting to be faster for simple specifiers. If they have any further formatting, such as width, precision or justification, then it might not necessarily be faster.

How does this magic work? Every time we call for e. This is done in the java. Formatter parse method, which used the following regex to break up the formatting elements:. In the pre code, parse would always start by applying the regex to the format String.

However, in Java 17, we instead try to parse the format String manually. If all the FormatSpecifiers are "simple", then we can avoid the regex parsing. If we do find one that is not simple, then it parses from then onwards. This speeds up the parsing by a factor of 3 for simple format Strings. Here is a test program where I parse the following Strings:. We pass these Strings to the private Formatter parse method using MethodHandles and measure how long it takes in Java 16 and We can thus expect a big difference with format strings that have simple fields, which would constitute the vast majority of cases.

Well done to Claes Redestad for putting in the effort to make this faster. I'm going to stick with my advice to use String. Here is the test code in case you'd like to try it yourself. We use the following JVM parameters: -showversion --add-opens java. We are always happy to receive comments from our readers. But format can do a lot of extremely useful things with numbers, dates, etc.

See java. Formatter API, which is actually used by String. Python Javascript Linux Cheat sheet Contact. StringBuilder java. String : java. StringBuilder [25] 25 invokevirtual java.