ImmutableList

ImmutableList is similar to the common java.util.List: it contains a list of elements. However, the big differences are

• ImmutableList is immutable, so it can not be modified
• ImmutableList is generating elements on request only, and does not keep the elements.

As a simple comparison, suppose you need a list of all integers between 1000 and 2000. You could write a loop to fill 1000 elements of an ArrayList. Alternatively, you can create an ImmutableList instance where get(n) creates and returns the expected element on request.

This mechanism is especially useful when large lists are used, or when you already know that the user of the list will only pick a few items from the list, or even just wants to know the size of the list.