This is Ian Darwin’s repackaging of Hirondelle Systems’s Date4J API.
Think of date4j as "the small, simple, sensible Date API for Java."
Another take: "One class to date them all". Literally, one class for almost everything.
Read all about it on https://github.com/johanley/date4j.
But do note that the problems that lead to the creation of date4j have been solved in all modern releases of Java! The Java 8 "new date/time API" (JSR-310, package java.time) has what you need; see https://docs.oracle.com/javase/tutorial/datetime/
Find the current version in Maven Central for use in Maven, Gradle, Buildr, Ivy, Grape, etc. Note that the Maven package is hirondelle-date4j.
Remember, today one might just as well use java.time.* instead.
The code’s original author is not a fan of Maven, but he thoughtfully put it under the BSD license, and his web page links to my redistribution, this is my "Redistribution and use in source and binary forms" with an intent to make it available to all Maven/Gradle/Buildr/etc Nexus/MavenCentral users.
I originally said that: I have made no code changes, and plan to make none. However, that is no longer strictly true; since the original author has not updated his code in five years, I’ve taken it upon myself to add a module-info file, just declaring the package itself. There are no external dependencies, so that’s valid. This should help those wanting to use date4j with JPMS, JigSaw, the Java Modules System, whatever you call Java Modules.
I have however reorganized the code into standard Maven/Gradle directory structure, added the POM file, removed the lib directory’s only file JUnit.jar (replaced with a Maven depends), and set this up for inclusion in Maven Central and uploaded it (URL above).