Declaring a List field with the final keyword

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.

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.