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When i shoud use an arrayMap instead of an arraylist? I read the documentation but it seems that they are interchangeable,so can someone provide me an example of when is better to use one and when the other?

Matteo Crosilla
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From the official docs:

ArrayMap is a generic key->value mapping data structure that is designed to be more memory efficient than a traditional HashMap, this implementation is a version of the platform's android.util.ArrayMap that can be used on older versions of the platform. It keeps its mappings in an array data structure -- an integer array of hash codes for each item, and an Object array of the key/value pairs.

So in short, ArrayMap is a Key-Value data structure. On the other ArrayList is just a List of elements (which behind the curtain uses an Array to manage those elements)

Rene Ferrari
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  • Thanks,can you give me a quick example? – Matteo Crosilla Feb 08 '19 at 09:25
  • A List in general should always be used if you have elements in an undefined quantity. Lets say you fetch users from a database: Since you don't know how many users you will get, so using an Array is not a viable option. That's a usecase for a List. There is a difference between ArrayList and LinkedList though and when to use which is dependent on the usecase ([check this out for more information](https://stackoverflow.com/questions/322715/when-to-use-linkedlist-over-arraylist-in-java)) – Rene Ferrari Feb 08 '19 at 09:28
  • ArrayMap is - in its core - similar to SharedPreferences in the sense that the structure of both is the same -> a key value store. With an ArrayMap you could for example (though not the most useful usecase ;D) map your users fetched from the database by using their Id as key and the User object as value. – Rene Ferrari Feb 08 '19 at 09:36