How to fix incompatible types with array of objects in list

Question

I have a problem with the code below. Compiler says incompatible types, java.lang.object[][] required but found java.lang.object[].

Anyone have an idea why this is? I've found some about generics that gives problems here but no solution to my problem.

Object sqlQuery[][] = null;

List<Object[]> sqlLista = new ArrayList<Object[]>();
   while (resultSet.next()) {
      sqlLista.add(new Object[] { false, resultSet.getString("MMITNO"), null, null, null, null, null } );
   }

sqlQuery = sqlLista.toArray();

edit: I have edited the code above as i see i had made a mistake with the dimensions

Jon Skeet · Accepted Answer · 2011-11-02 10:05:47Z

The problem is that you're calling the parameterless overload of toArray(), which returns Object[]. You can't assign an Object[] to an Object[][] variable.

Now it seems to me that you possibly actually want to make sqlQuery an Object[][][] instead of an Object[][], so that you get one two-dimensional array per entry in the result set. You'd then have:

// Please use this form rather than putting the brackets after the name
// - it keeps all the type information together.
Object[][][] sqlQuery = null; // No point giving it a dummy value

List<Object[][]> list = new ArrayList<Object[][]>();
...
sqlQuery = list.toArray(new Object[0][][]);

However, I'd strongly advise you not to go down this route anyway - encapsulate the "result" concept which is currently just Object[][] in a new type, so you'd have:

Result[] sqlQuery = null;

List<Result> list = new ArrayList<Result>();
...
sqlQuery = list.toArray(new Result[0]);

This will be a lot easier to reason about - even if Result only contains an Object[][].

Alexandr · Accepted Answer · 2011-11-02 10:09:18Z

3

sqlLista.toArray();

returns array where each element = Object[][], the return array's type is not Object[][] itself.

Change your code onto:

Object sqlQuery[][] = new Object[][] { };

List<Object[]> sqlLista = new ArrayList<Object[]>();
   while (resultSet.next()) {
      sqlLista.add(new Object[] { false, resultSet.getString("MMITNO"), null, null, null, null, null } );
   }

sqlQuery = sqlLista.toArray();

answered Nov 2, 2011 at 10:09

Alexandr

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S.L. Barth is on codidact.com · Accepted Answer · 2011-11-02 10:06:22Z

0

Look at the declaration of List.toArray().

It wants to convert to an array of Object (Object[]). But sqlQuery is declared as an array of an array of Object (Object[][]).

What to do from here depends on what you want to achieve with your code. You may want to create a specific class for a row, and create a List of instances of that class, instead of an array of Object[][].

answered Nov 2, 2011 at 10:06

S.L. Barth is on codidact.com

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