How to convert an arraylist to a multidimensional array

Question

I have an ArrayList object which its values are arrays of Object . I want to convert it to an array. This is the summary of what i did:

ArrayList result = new ArrayList();
Object[] row = new Object[4];
result.add(row);
Object[][] arrayResult = result.toArray();

but I get an error that i can't cast it to an Object[][] . What should I do?

Answer 1

Change it to something like these:

ArrayList<Object> result = new ArrayList<Object>(); // 1
Object[] row = new Object[4];
result.add(row);
Object[][] arrayResult = result.toArray(new Object[0][0]); // 2

1. You should have a type parameter (don't really affect the error, but good practice).
2. toArray with no arguments would just give you a Object[] , you need to give it an array as a "example" . This is caused by something called "type erasure", which you can read a bit from here .