How to convert object class to arrayList ? java [duplicate]

List<Integer> users = new ArrayList<Integer>();

Map<String, Object> hashMap = new HashMap<String, Object>();
hashMap.put("users",user);
....
....
....
List<Integer> users = (List<Integer>)hashMap.get("users"); //assuming this is another method and 'users' is not defined here yet
Integer[] usersArray = users.toArray(new Integer[users.size()]);
System.out.println("" + usersArray[i]);

Please note that this is an atrocity and you shouldn't be storing that List as an Object, you are pretty much circumventing what Generics are for.

This code will work if you want to access it as an ArrayList:

List<Integer> users = new ArrayList<Integer>();
Map<String, List<Integer>> hashMap = new HashMap<String, List<Integer>> ();
hashMap.put("users",users);
hashMap.get("users");

Your code won't work since you were storing it as an Object. So you would need a cast. And even then you use [] for arrays, not ArrayLists

If you want to use it as an array you can change the last line to:

hashMap.get("users").toArray()

And then you can use [1], or just do .get(1) on the initial code.

Alternatively, if you want to use hashMap as a property bag as someone validly mentioned you would need to do a cast:

((ArrayList<Integer>) hashMap.get("users"))

Then you can use users as an ArrayList as you are getting an Object by default from the HashMap.

You can try something like following

List<Users> usersList = new ArrayList<>();
Map<String,List<Users>> hashMap = new HashMap <> ();
hashMap.put("user",usersList);

Now

hashMap.get("user")

Will return a List of Users, Now you can use

hashMap.get("user").get(0); // to get 0th index user

Because it is ArrayList and not array,You can get it like this-

public static void main(String args[]) throws Exception
{
  ArrayList<Integer> users = new ArrayList<Integer>();
  users.add(5);
  users.add(10);

  Map <String,Object> hashMap = new HashMap <String,Object> ();

  hashMap.put("users",users);

  ArrayList<Integer> no =  ((ArrayList<Integer>) hashMap.get("users"));

   for (Integer integer : no) {
    System.out.println(integer);
   }
}

output-

5
10

Now to convert ArrayList to Array -

Integer[] arr = no.toArray(new Integer[no.size()]);