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ArrayDeque is implemented as an array, why is it not Random Access?

I know that ArrayDeque is fast when adding and removing simple lists. I tested it, it was quicker to add and delete than LinkedList. Because I know that it is implemented as an Array, so why not Random Access?

I read the ArrayDeque.java file in the Java src. But I do not understand it well with my English level. I've seen a lot of articles from Google and Stack Overflow, but I did not get the answers I wanted.

In conclusion, what I'm looking for is:

  1. Why is ArrayDeque not Random Access? (I am most curious)
  2. In what situations is ArrayDeque used?
  3. Is ArrayDeque not implemented as an Array? (Did I misunderstand this?)

Thank you very much for your reply!

Solution

  • As mentioned in here, ArrayDeque is resizable-array implementation of the Deque interface. Underlining data-structure is Array. However, it doesn't support random access because it exposes double-ended queue interface. If you want to access a random element of Deque, you can invoke toArray() and then access elements by index.