Casting primitive wrap type variable to primitive

Question

We have this code:
float f = 22.2f;
System.out.println((int)f);
Which prints out "22".
Float f = 22.2f;
System.out.println((int)f);
When i changed the variabile type from float to Float, code throw up a compile a error, that Float type cannot be casted to int. Can somebody tell me what's going on? Isnt compiler supposed to do unboxing the variable to primitive float and then primitive float to be casted to an int?
System.out.println((int)f.floatValue());
Isnt that what the compiler is supposed to do? Code which works perfectly fine.
Thank for your help.

Answer 1

Hello vcraescu,
I think you are wondering why the compiler does not convert from Float to float (unboxing) and subsequently from float to short (your cast), so the bug report probably does not help you too much.
Casts come into play when the compiler can not assure that the statement is semantically correct. The bytecode would be the same with or without the cast (if the compiler would accept omitting casts).
Casting primitives:
int i = 0;
short s = (short)i;Purpose of the cast: The compiler has no idea whether the two higher bytes are relevant and you therefore need to specify that they are not.
Casting reference types:
With reference types there are two types of casts, the upcast and the downcast.
class Exampe {
     public static void example(Object... objects) {
          for (Object object : objects) {
               System.out.print(object);
               System.out.print(' ');
          System.out.println();
     public static void main(String[] args) {
          Object[] objects = { "String", 123, 1.23 };
          example(objects);
          example((Object) objects);
}The purpose of this (up)cast is that you want the object to be treated as beeing of a more general type.
org.w3c.dom.Node node;
switch(node.getNodeType()) {
     case org.w3c.dom.Node.ELEMENT_NODE:
          org.w3c.dom.Element element = (org.w3c.dom.Element) node;
     case org.w3c.dom.Node.TEXT_NODE:
          org.w3c.dom.Text element = (org.w3c.dom.Text) node;
     default:
}These casts tell the compiler that you are certain the object node is of a more specific type.
My point is that all these casts have a distinct purpose. Your cast on the other hand does not. Looking at your code I see a conversion from a wrapper to a primitive, not necessarily the loss of precision connected with it and that is what this cast should be about.
With kind regards
Ben Schulz