Why is Wrapper Integer to Float conversion not possible in java

Question

Why the typecasting of Wrapper Float does not works in java for Wrapper Integer type.

public class Conversion {
    public static void main(String[] args) {
        Integer i = 234;

        Float b = (Float)i;

        System.out.println(b);

    }
}

Answer 1

An Integer is not a Float. With objects, the cast would work if Integer subclassed Float, but it does not.

Java will not auto-unbox an Integer into an int, cast to a float, then auto-box to a Float when the only code to trigger this desired behavior is a (Float) cast.

Interestingly, this seems to work:

Float b = (float)i;

Java will auto-unbox i into an int, then there is the explicit cast to float (a widening primitive conversion, JLS 5.1.2), then assignment conversion auto-boxes it to a Float.

Answer 2

You are asking it to do too much. You want it to unbox i, cast to float and then box it. The compiler can't guess that unboxing i would help it. If, however, you replace (Float) cast with (float) cast it will guess that i needs to be unboxed to be cast to float and will then happily autobox it to Float.