java Array.newInstance throws ClassCastException, why?

Question

Very simple code:

    int[] a = new int[]{4,1,2,3};
    Array a3 = (Array) Array.newInstance(a.getClass(), a.length);

It throws an exception 'Exception in thread "main" java.lang.ClassCastException: [[I cannot be cast to java.lang.reflect.Array'

Where did I get wrong and how to fix it?

Are you trying to create a new int[] array or a new int[][] array? — khelwood
– khelwood, Commented Nov 20, 2018 at 11:08

Eran · Accepted Answer · 2018-11-20 11:12:38Z

5

Array.newInstance(a.getClass(), a.length) creates a two dimensional int array (that's what happens when you create an array whose element type is an int[]), so it should be:

int[][] a3 = (int[][]) Array.newInstance(a.getClass(), a.length);

Array is a class used to create array instances with reflection, but array instances are not instances of that class.

BTW, if you intended to create a one dimensional int array (i.e. int[]), you should write:

int[] a3 = (int[]) Array.newInstance(int.class, a.length);

edited Nov 20, 2018 at 11:12

answered Nov 20, 2018 at 11:07

Eran

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