How to convert an ArrayList containing Integers to primitive int array?

Question

I\'m trying to convert an ArrayList containing Integer objects to primitive int[] with the following piece of code, but it is throwing compile time error. Is it possible to

Answer 1

Arrays.setAll() will work for most scenarios:

1. Integer List to primitive int array:

   public static int[] convert(final List list)
   {
      final int[] out = new int[list.size()];
      Arrays.setAll(out, list::get);
      return out;
   }
   

2. Integer List (made of Strings) to primitive int array:

   public static int[] convert(final List list)
   {
      final int[] out = new int[list.size()];
      Arrays.setAll(out, i -> Integer.parseInt(list.get(i)));
      return out;
   }
   

3. Integer array to primitive int array:

   public static int[] convert(final Integer[] array)
   {
      final int[] out = new int[array.length];
      Arrays.setAll(out, i -> array[i]);
      return out;
   }
   

4. Primitive int array to Integer array:

   public static Integer[] convert(final int[] array)
   {
      final Integer[] out = new Integer[array.length];
      Arrays.setAll(out, i -> array[i]);
      return out;
   }