Cast List to Object[][] in Java

Question

How to turn List of arrays into two dimensional array in Java?

//Prepare the list
List<Object[]> conf = new LinkedList<Object[]>();
conf.add(new Object[]{ "FOO", "BAR"});
conf.add(new Object[]{ "FOO", "BAR"});

I tried:

Object[][] array = (Object[][]) conf.toArray(new Object[0]);

But it fails at ClassCastException:

java.lang.RuntimeException: java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to [[Ljava.lang.Object;

http://stackoverflow.com/questions/9572795/convert-list-to-array-in-java — flup, Apr 10 '13 at 07:49
this is what you want http://stackoverflow.com/questions/5803619/java-convert-a-list-of-array-into-an-array-of-array — BevynQ, Apr 10 '13 at 07:52

score 9 · Accepted Answer · answered Apr 10 '13 at 07:51

9

You are missing a pair of square brackets:

    Object[][] array = conf.toArray(new Object[0][]);
                                                 ^^

Or, if you wish to save on one unnecessary memory allocation:

    Object[][] array = conf.toArray(new Object[conf.size()][]);

The cast to Object[][] is unnecessary once the argument to toArray() has the correct type.

answered Apr 10 '13 at 07:51

NPE

1

The cast to `Object[][]` is not necessary. – Vincent van der Weele Apr 10 '13 at 07:54

1 Answers1