Declaring a List field with the final keyword

Question

If I have the following statement within a class where Synapse is an abstract type:

private final List<Synapse> synapses; 

Does final allow me to still be able to change the state of the Synapse objects in the List, but prevent me from adding new Synapse objects to the list? If I am wrong, could you please explain what final is doing and when I should be using the keyword final instead.

Answer 1

No, the final keyword does not make the list, or its contents immutable. If you want an immutable List, you should use:

List<Synapse> unmodifiableList = Collections.unmodifiableList(synapses); 

What the final keyword does is prevent you from assigning a new value to the 'synapses' variable. I.e., you cannot write:

final List<Synapse> synapses = createList(); synapses = createNewList(); 

You can, however, write:

List<Synapse> synapses = createList(); synapses = createNewList(); 

In essense, you can still change, add and remove the contents of the list, but cannot create a new list assigned to the variable synapses.

Answer 2

final prevents you from reassigning synapses after you've assigned it once - you can still add/remove elements as you would normally. You can read more about the final keyword here.