Considering object encapsulation, should getters return an immutable property?

Question

When a getter returns a property, such as returning a List of other related objects, should that list and it\'s objects be immutable to prevent code outside of

Answer 1

It depends on the context. If the list is intended to be mutable, there is no point in cluttering up the API of the main class with methods to mutate it when List has a perfectly good API of its own.

However, if the main class can't cope with mutations, then you'll need to return an immutable list - and the entries in the list may also need to be immutable themselves.

Don't forget, though, that you can return a custom List implementation that knows how to respond safely to mutation requests, whether by firing events or by performing any required actions directly. In fact, this is a classic example of a good time to use an inner class.