Question:
What is the difference between List and ArrayList . I googled, but didn’t really find anything (at least in Russian). As far as I understand, ArrayList is an implementation of List , but I didn't notice much difference. So what's the difference anyway?
Answer:
Since ArrayList implements the List interface, it must have all the List methods plus (possibly) some others. Hence the resemblance. At the same time, these methods are not implemented in List at all and it is impossible to create an object with the new List() command.
Implementations of the same interface may have the same methods externally, but radically differ in their internal implementation. For example, at the heart of ArrayList is an array, which, if necessary, is replaced with a larger (or smaller) size, overwriting the contents from the old to the new. LinkedList (another implementation of the List interface) is based on a doubly linked list, and each element of the list contains a link to the next and previous elements.