why the code is giving the answer as -1

[Vinay Belagavi]

Hi, can anyone explain me why the below code is giving the answer as
-1?
public class DoubleDemo
{
public static void main(String[] args)
{
double d1=1.0;
double d2=0.0;
byte b=1;
d1=d1/d2;
b=(byte)d1;
System.out.println(b);
}
}

[Barry Gaunt]

Read my comments in the snippet below:

d1=d1/d2;  // here d1 becomes Double.POSITIVE_INFINITY
b=(byte)d1; // this converts first to [B]int[/B] and then casts to [B]byte[/B]
            // so d1 -> Integer.MAX_VALUE followed by taking
            // the 8 least significant bytes of Integer.MAX_VALUE which
            // are all ones. So the result in b is 11111111 which is -1.

Here's the byte code of your program:

  Code:
   0:   dconst_1
   1:   dstore_1
   2:   dconst_0
   3:   dstore_3
   4:   iconst_1
   5:   istore  5
   7:   dload_1
   8:   dload_3
   9:   ddiv  
   10:  dstore_1
   11:  dload_1
[B]   12:  d2i                         // double to int
   13:  i2b                         // int to byte
 [/B]  14:  istore  5
   16:  getstatic       #2; //Field java/lang/System.out:Ljava/io/PrintStream;
   19:  iload   5
   21:  invokevirtual   #3; //Method java/io/PrintStream.println :( I)V
   24:  return
    

[ October 14, 2006: Message edited by: Barry Gaunt ]

[Vinay Belagavi]

Thanks for the reply Barry.