Need Help Converting a long to a Byte Array

[Randall Stevens]

I have a constant and it is a long data type. I need to convert it to a byte array. I have been looking at the Byte parseByte(), but it appears to return a single byte.
What do I need to do in order to convert from a long to a byte array?

[Wayne L Johnson]

It ain't pretty, but it works. It's a matter of using the shift operators to pull out 8 bits at a time. Note that it fills the array from the bottom (bytes[7]), but prints it out in *normal* order. It also destroys the "bigValue" so that by the end it has a value of zero.

public class LongToByteArray {
   public static void main(String[] args) {
      long bigValue = 123456789000L;
      byte[] bytes = new byte[8];
      for (int i=bytes.length-1;  i>=0;  i--) {
         bytes[i] = (byte)(bigValue & 0x000000ff);
         bigValue >>= 8;
      }
      System.out.println("Big Value: " + bigValue);
      for (int i=0;  i<bytes.length;  i++) {
         System.out.println(bytes[i] + " ");
      }
   }
}

There may be prettier ways of doing it, but it seems to work. In a real application you'd want to encapsulate the logic in a separate method.
[ October 22, 2003: Message edited by: Wayne L Johnson ]

[Randall Stevens]

in a 32-bit architecture, wouldn't it be 4 bytes and not 8 as your code suggests?

[Wayne L Johnson]

In Java, anything of type "long" is 64 bits, guaranteed, regardless of what the underlying architecture or OS is. That's why I hard-coded it to 8 bytes.
If Java tried to rely on the underlying OS to determine what a "long" was --or any primitive--then you might have this problem. That's why, in order to ensure "write once, run anywhere," Sun made sure to define the eight primitives, and every JVM honors those definitions. A "long" is a 64-bit signed two's-complement integer.

[Michael Fitzmaurice]

Hi
You could also chain a java.io.DataOutputStream to a java.io.ByteArrayOutputStream - see the API docs for details. I also once wrote a class to do such conversions without using the various IO streams - you can find it online here.
Hope this helps
Michael