As Josh Bloch said: Classes should be immutable unless there's a very good reason to make them mutable Immutability makes life a LOT easier. A great example i

As Josh Bloch said: Classes should be immutable unless there's a very good reason to make them mutable Immutability makes life a LOT easier. A great example is the well designed joda-time vs the disaster that is the the mutable Date and Calendar core language classes.