Can I somehow implement bracketed casting between Double and Integer classes in Java?

Question

I know Java doesn't allow direct casting between Integer and Double classes like so:

var intList = new ArrayList<Integer>();
// code that fills intList with Integer entries

var doubleVal = (Double) intList.get(0); // Class Cast exception

I also know the reason why and the solution(s) to this.

My question is - is there a way to make this work? Can I implement something such that when I use (Double) intList.get(0) in my code, it actually gives me what I want instead of throwing an exception?

In C# I would simply override the cast operator to do this and it would work, but sadly Java doesn't allow that.

Answer 1

Can I somehow implement bracketed casting between Double and Integer classes in Java?

Basically no. There are no Java tricks that you can use to make a simple (Double) cast do what you want to happen here.

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Your example expression (Double) intList.get(0) requires too many conversions for the compiler to be "happy". It needs to unbox the Integer to an int , widen it to a double , and then box it as a Double . Three conversions.

You have to give it some help. Here are some of the ways you could help:

  (Double) ((int) intList.get(0))

The cast to int causes the Integer to be unboxed. From there it can be widened to a double and then auto-boxed to a Double .

  (Double) (intList.get(0).doubleValue())

This does the Integer to double via the doubleValue call, and then the (Double) does the final step.

  Double.valueOf(intList.get(0).doubleValue())

As above but using an explicit call to do the boxing.