Why java.util.Date Had to Go If you have ever tracked down a bug caused by a SimpleDateFormat shared across threads, or spent an afternoon understanding why a Calendar.get(Calendar.MONTH) returns 0 for January, you will appreciate why JSR-310 was one of the most eagerly anticipated Java 8 features. The new java.time API is not a patch on the old API — it is a complete redesign that makes an entire class of date and time bugs impossible by construction.