I believe String.format is new with Java 1.5 but java.text.MessageFormat was in 1.4.2. Both allow you to format strings, but do it very differently. String.format looks a lot like C++ printf. Any idea why Java 5 added String.format if MessageFormat was already available? Besides the fact that String.format looks a little easer to use to an old C programmer, are there other reasons for using it instead of MessageFormat? My next project will have a lot of complex text formatting, and I am wondering if being able to use String.format is a reason to move up to Java 1.5 from 1.42. If anyone has experience with either of these classes, please let me know your opinions.
Yes, String.format was introduced in Java5, along with Scanner and Formatter; if I remember correctly, String.format uses Formatter.
The % tags (which date back to C in the early 1970s, maybe even farther back look for "the March of Progress") are much easier to use than the DecimalFormat classes which appear to be called by MessageFormat. Most of us who remember DecimalFormat were only too pleased to be able to use % tags. For details of the % tags, look under Formatter in the API documentation.