make arrayList.toArray() return more specific types

java arrays object types arraylist
kamikaze_pilot picture kamikaze_pilot · Feb 21, 2011 · Viewed 161.1k times · Source

So, normally ArrayList.toArray() would return a type of Object[]....but supposed it's an Arraylist of object Custom, how do I make toArray() to return a type of Custom[] rather than Object[]?

Answer

Mihai Toader picture Mihai Toader · Feb 21, 2011

Like this:

List<String> list = new ArrayList<String>();

String[] a = list.toArray(new String[0]);

Before Java6 it was recommended to write:

String[] a = list.toArray(new String[list.size()]);

because the internal implementation would realloc a properly sized array anyway so you were better doing it upfront. Since Java6 the empty array is preferred, see .toArray(new MyClass[0]) or .toArray(new MyClass[myList.size()])?

If your list is not properly typed you need to do a cast before calling toArray. Like this:

    List l = new ArrayList<String>();

    String[] a = ((List<String>)l).toArray(new String[l.size()]);

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