Ada and Java. different behaviour. casting long to int problem.

[nabbasi@pacbell.net]

This below shows that Ada detected at compile time a basic problem
that the Java compiler missed. (this might be specific problem
with the Java compiler I am using), it also could be a 
mis-understanding on my part of the Java semantics when it 
comes to this, but the bottom line is that Java produced, 
what for me, can only be a wrong result.

Please do not make this thread a language-war, (I happen to
like both Java and Ada), but I am really only interested in 
someone explaining the justification behind this Java behavior.

In the example, I cast a long integer literal, outside the range
of an integer, into an integer variable.  Java allows this,
and produces the wrong result. Ada compiler detect this as an error
at compile time, and it also detects the same thing at run-time.

fyi: a 64 bit signed long range is -9223372036854775808 .. 9223372036854775807 
and an 32 bit signed integer range is  -2147483648 .. 2147483647

In the example, I cast the literal 3200000000, which is clearly outside
the range of an integer, into an integer. I expect the compiler or
the run-time, to detect this. Ada does, Java did not. Is this by 'design'
on the part of Java? i.e. is this how Java supposed to behave? becuase
this can result in very wrong calculations if not detected.

env:
----
OS: linux 2.0.36
Java compiler: free JDK from http://www.blackdown.org 1.2, also 1.1.7B
Ada compiler : free ada95 GNAT compiler from http://www.gnat.com, version 3.11p

---------------- java example 1-----------------------------
class test_cast
{
   public static void main(String args[])
   {
      long n= 3200000000L;
      int  m= (int) n;
      System.err.println("long n =" + n + " int m=" + m);
   }
}

$javac  ./test_cast.java      <-- compile OK

$java test_cast               <--- runs OK and produces 'wrong' result.
long n =3200000000 int m=-1094967296
$
----------------------------- Ada example 2 -----------------
with Ada.Text_Io;         USE Ada.Text_Io;

procedure Test_Cast is
   n : Long_Integer := 3200000000;
   m : Integer      := Integer (N);
begin
      Put_Line (   "long n ="  &  Long_integer'Image(N)
                 & "int  m ="  &  Integer'Image(M) );
end Test_Cast;

$gnatmake test_cast.adb
gnatgcc -c test_cast.adb
test_cast.adb:5:24: value not in range of type "Standard.Long_Integer"
test_cast.adb:5:24: static expression raises "Constraint_Error"
gnatmake: "test_cast.adb" compilation error
$

--------------------------------------------------------------------

Now, lets try the same idea as above, but do not use a literal
number (so to not allow the ada compiler the chance to detect this
at compile time) and try to do the same at run-time.


------------------- ada example 2 -----------------------------

with Ada.Text_Io;         USE Ada.Text_Io;

procedure Test_Cast is
   N  : Long_Integer;
   M  : Integer;
   package Long_Int_Io  is new Ada.Text_Io.Integer_Io(Long_Integer);
begin
   Long_Int_Io.Get(N);
   M := Integer (N);

   Put_Line (   "long n ="  &  Long_integer'Image(N)
              & "int  m ="  &  Integer'Image(M) );
end Test_Cast;

$gnatmake -gnatf test_cast.adb    <-- compile OK
gnatgcc -c -gnatf test_cast.adb
gnatbind -x test_cast.ali
gnatlink test_cast.ali

$./test_cast                  <--- run
3200000000

raised ADA.IO_EXCEPTIONS.DATA_ERROR   <-- exception raised
-------------------------------------------------------------


comments?

Nasser