java.util.arraylist cannot be cast to java.lang.object[]

Question

So in my code below, line marked with *** gives me the exception

java.util.arraylist cannot be cast to java.lang.object[]

I am trying to retrieve a list of users from backendless. I have created a list view that works when normally adding to list. but not when trying to get the response(Object)

public class UserRolesActivity extends AppCompatActivity {

    ListView userListView;
    TextView changeRoleTv;
    List<String> list;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_user_roles);

        userListView = (ListView) findViewById(R.id.usersListView);
        list = new ArrayList<>();
        changeRoleTv = (TextView) findViewById(R.id.chooseUserChangeTv);

        Backendless.Data.mapTableToClass("Users", Users.class);

        list.add("Name1");
        list.add("Name2");

        RetrieveUsers retrieveUsers = RetrieveUsers.getInstance();

        retrieveUsers.getUsersAsync(new AsyncCallback<Object>() {
            @Override
            public void handleResponse(Object response) {

                try{
                 ***   Object [] result = (Object []) response;   ***
                    List<Object> user = Arrays.asList(result);

                    for (int i = 0; i< user.size(); i++){

                        if (user.get(i) != null){
                            list.add(((Learner) user.get(i)).getFirstName().toString() + ": " + ((Learner) user.get(i)).getLastName().toString());
                        }
                    }

                }catch (Exception e){
                    ShowToast(e.getMessage().toString());
                }

                userListView.setAdapter(new ArrayAdapter<String>(getApplicationContext(), android.R.layout.simple_list_item_1, list));


            }

            @Override
            public void handleFault(BackendlessFault fault) {
                ShowToast(fault.getMessage());
            }
        });

    }

    private  void ShowToast(String message)
    {
        Toast.makeText(this, message, LENGTH_LONG).show();
    }

}

If you really need an array: ((List<?>) response).toArray(). But it's a List, and you wrap the array into a List. So List<Object> user = (List<Object>) result; would work. — Andy Turner
– Andy Turner, Commented Aug 31, 2017 at 15:23

Shailendra Sinha · Accepted Answer · 2017-08-31 15:27:35Z

1

response is of type java.uti.ArrayList wrapped under Object type. You can not cast
Arraylist to Array of Object.

answered Aug 31, 2017 at 15:27

Shailendra Sinha

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2 Comments

Franco Landman Over a year ago

So what is the best way to get the User Objects from the response object?

Shailendra Sinha Over a year ago

Possible option could be updating method getUsersAsync to accepts new AsyncCallback<List<Users>() { @Override public void handleResponse(<List<Users>response) { -- // Not sure you have access to method Other Option could Cast Object directly to List<Users> List<Object> user = List<Object>(response); Note: assuming your response actual type is List<Users>.

MartinByers · Accepted Answer · 2017-08-31 15:32:12Z

0

what you are doing looks a bit long winded:

***   Object [] result = (Object []) response;   ***
List<Object> user = Arrays.asList(result);

    for (int i = 0; i< user.size(); i++){

       if (user.get(i) != null){
           list.add(((Learner) user.get(i)).getFirstName().toString() + ": " + ((Learner) user.get(i)).getLastName().toString());
       }
    }

could be condenced to :

List<?> users = (List<?>)response;
for (Object user : users) {
    if (user != null){
        // Some stuff
    }
}

Next you will get an issue with:

       list.add(((Learner) user.get(i)).getFirstName().toString() + ": " + ((Learner) user.get(i)).getLastName().toString());

because user.get(i)).getFirstName().toString() + ": " is a String which you are then casting to Type Learner. You will need to rethink this.

answered Aug 31, 2017 at 15:32

MartinByers

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1 Comment

Franco Landman Over a year ago

Thanks, didn't solve everything but helped alot. Yeah the Learner Cast at the bottom was from trying another class and table. I noticed it as soon as I posted.

cs95 · Accepted Answer · 2019-07-02 06:16:37Z

0

you can define your result as

Object[] arr = new Object[]{...};

edited Jul 2, 2019 at 6:16

cs95

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answered Aug 31, 2017 at 15:40

TankRaj

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Comments

Šimon Vyhnis · Accepted Answer · 2021-10-13 21:29:52Z

0

To convert List<Object> to array of objects use .toArray() method:

Object[] result = response.toArray();

That's the solution to the original exception.

answered Oct 13, 2021 at 21:29

Šimon Vyhnis

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