Can't cast array Object to double[]

Question

I read where an array of int can't be cast as double[]: Casting Don't Work int[] to double[], 17 Oct

I have run into a similar roadblock trying to cast an array Object of doubles to double[]. I suspect it is the same issue.

I would like to understand the limitation better. Is this a general limitation on all collections, or is it limited to arrays? Is there a fundamental reason for the limitation, or is it just something that has to be worked around?

I have a class that creates an array of doubles that represents an input signal. I pass an instance of that class to a class to calculate the FFT of the signal. The FFT class I'm using needs a double[] parameter. Since I create the input array as double[], it seems I should be able to cast it as such.

Answer 1

trying to cast an array Object of doubles to double[]

There is no such thing as 'an array Object of doubles' in Java. There is double[], there is Double[], and there is Object[] where the elements are Doubles.

You can cast between the last two, in both directions if the underlying type really is Double[], but not between the first and either of the others.

Answer 2

The problem is explained here Why covariance and contravariance do not support value type . Covariance and contravariance does not work with value types. However, you can force the cast by using linq as Will mentioned.