CAFEBABE

[O. Subramaniam]

couple of days before i took a technical test in java.
the first questions was "What is CAFEBABE in Java?" can anyone
explain to me what it is?

[Maulin Vasavada]

hi
look for that on google and u'll find more
CAFEBABE is a magic word for a class file. as u might observe it is consisting of only hex letters. if the class file doesn't have this magic word then it is not a valid class file (well i'm myself little unsure about this on various systems Windows/Linux/Unix as magic word is used by mostly Unix based systems so i donno if Windows jvm cares about CAFEBABE or not)...
regards
maulin.

[O. Subramaniam]

where this magical word will be stored, can v read this word?

[Vadiraj Deshpande]

Originally posted by O. Subramaniam:
where this magical word will be stored, can v read this word?

Hi,
Best option is to try out yourself. I found out from the net that "CAFEBABE" are
the starting bytes of each and every java class files.
So here is the program to find out the truth.

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
public class ReadBytesFromFile
{
public static void main(String[] args) throws IOException
{
if(args.length == 0)
{
System.out.println("\nUsage: java ReadFileBytes <fileToBeRead>");
System.exit(1);
}
File file = new File(args[0]);
FileInputStream fin = new FileInputStream(file);
int readByte = fin.read();
while(readByte != -1)
{
System.out.print(Integer.toHexString(readByte) + " ");
readByte = fin.read();
}
}
}
  

If we run this program using the command

java ReadBytesFromFile ReadBytesFromFile.class  

we see that the first bytes are indeed "CAFEBABE".
HTH
ALan

[Roy Tock]

Hmmm... under Windows, using cygwin's "od -t x2 blah.class" to show me what's in the file, I get "feca beba".
Not nearly as cool sounding as CAFEBABE.
[ August 14, 2003: Message edited by: Roy Tock ]

[Vadiraj Deshpande]

Originally posted by Roy Tock:
Hmmm... under Windows, using cygwin's "od -t x2 blah.class" to show me what's in the file, I get "feca beba".
Not nearly as cool sounding as CAFEBABE.
[ August 14, 2003: Message edited by: Roy Tock ]

May be because of platform encoding or with cygwin?
As you can see, if you reverse the hex words we get "CAFEBABE" again.

-A
[ August 18, 2003: Message edited by: Allan Deshpande ]