If you make any variable as final, you cannot change the value of final variable(It will be constant).
If you make any method as final, you cannot override it.
If you make any class as final, you cannot extend it.
What does it mean for a collection to be final in Java?
It simply means that the reference cannot be changed.
final List list = new LinkedList();
....
list.add(someObject); //okay
list.remove(someObject); //okay
list = new LinkedList(); //not okay
list = refToSomeOtherList; //not okay