convert an arrayList<Object[]> into a nested array

Question

This is the following idea:

List<Object[]> ret = new ArrayList<>();
ret.add(new Object[]{"a", 1});
Object[][] obj = (Object[][]) ret.toArray();

but it doesn't work: toArray returns Object[]

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

Any idea?

each element in the list would be an Object[]. Then, I want to cast it into what it really is — Bertuz
– Bertuz, Commented Jun 12, 2019 at 14:47

khelwood · Accepted Answer · 2019-06-12 15:02:18Z

5

There is a version of toArray that accepts an array as an argument. This allows you to specify what type of array you want returned.

Object[][] obj = ret.toArray(new Object[0][]);

You can pass in an array big enough to hold the contents of your list; or you can pass in an array of zero size and the list implementation should return a new array of the same type as the one you passed in.

edited Jun 12, 2019 at 15:02

answered Jun 12, 2019 at 14:51

khelwood

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1 Comment

Bertuz Over a year ago

yes! That's what's missing: passing the array into which the elements of the list are to be stored. Worked like charm.

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