/*non-public*/
static boolean canConvert(Class<?> src, Class<?> dst) {
// short-circuit a few cases:
if (src == dst || dst == Object.class) return true;
// the remainder of this logic is documented in MethodHandle.asType
if (src.isPrimitive()) {
// can force void to an explicit null, a la reflect.Method.invoke
// can also force void to a primitive zero, by analogy
if (src == void.class) return true; // or !dst.isPrimitive()?
Wrapper sw = Wrapper.forPrimitiveType(src);
if (dst.isPrimitive()) {
// P->P must widen
return Wrapper.forPrimitiveType(dst).isConvertibleFrom(sw);
} else {
// P->R must box and widen
return dst.isAssignableFrom(sw.wrapperType());
}
} else if (dst.isPrimitive()) {
// any value can be dropped
if (dst == void.class) return true;
Wrapper dw = Wrapper.forPrimitiveType(dst);
// R->P must be able to unbox (from a dynamically chosen type) and widen
// For example:
// Byte/Number/Comparable/Object -> dw:Byte -> byte.
// Character/Comparable/Object -> dw:Character -> char
// Boolean/Comparable/Object -> dw:Boolean -> boolean
// This means that dw must be cast-compatible with src.
if (src.isAssignableFrom(dw.wrapperType())) {
return true;
}
// The above does not work if the source reference is strongly typed
// to a wrapper whose primitive must be widened. For example:
// Byte -> unbox:byte -> short/int/long/float/double
// Character -> unbox:char -> int/long/float/double
if (Wrapper.isWrapperType(src) && dw.isConvertibleFrom(Wrapper.forWrapperType(src))) {
// can unbox from src and then widen to dst
return true;
}
// We have already covered cases which arise due to runtime unboxing
// of a reference type which covers several wrapper types:
// Object -> cast:Integer -> unbox:int -> long/float/double
// Serializable -> cast:Byte -> unbox:byte -> byte/short/int/long/float/double
// An marginal case is Number -> dw:Character -> char, which would be OK if there were a
// subclass of Number which wraps a value that can convert to char.
// Since there is none, we don't need an extra check here to cover char or boolean.
return false;
} else {
// R->R always works, since null is always valid dynamically
return true;
}
}
private static int ftypeKind(Class<?> ftype) {
if (ftype.isPrimitive()) return Wrapper.forPrimitiveType(ftype).ordinal();
else if (VerifyType.isNullReferenceConversion(Object.class, ftype)) return FT_UNCHECKED_REF;
else return FT_CHECKED_REF;
}
