Version 4.0.0 of iCal4j will introduce many changes to the library in order to support the new Java Date/Time API (JSR-310). If you would like to get a feel for the changes you can now download an Alpha build from Maven Central.
The release notes has a full list of changes compared to the current 3.x release, so please have a look to see what is included in the 4.x uplift.
Note that this build has many bugs and currently not all the unit tests are passing. So there may be further changes to the API and the underlying functionality.
We welcome any feedback and bug reports via the Github issues page.