Add one day into Joda-Time DateTime

If you want add days to current date time instance, use MutableDateTime

MutableDateTime dateTime = new MutableDateTime(date);  
dateTime.addDays(1);

The plusDays method is not a mutator. It returns a copy of the given DateTime object with the change made rather than changing the given object.

If you want to actually change the variable dateTime value, you'll need:

DateTime dateTime = new DateTime(date);
dateTime = dateTime.plusDays(1);