Strange prob... to get correct o/p we have to run this prog twice ?????????

Question

hi,
my problem is that i have created one bat file and i want to run that file in java but it is not running properly. the problem is .......
i have created one bat file named "file1.bat" & content of this file is as follows :-
[ ag > b.txt]
(and content of file "ag" is "aaaaaaa" )
now i am trying to run this bat file in java and want to read this b.txt in which i have redirected the content of file "ag".
for that i have written the code like this:-file name is "runbf.java"
import java.awt.*;
import java.lang.Runtime;
import java.io.*;
public class DriveVol
public static void main(String args[]) throws IOException
int volumn;
Runtime r = Runtime.getRuntime();
r.exec("ss.bat");
FileInputStream fp;
fp = new FileInputStream("b.txt");
flush();
do
volumn = fp.read();
System.out.print((char)volumn);
}while(volumn != -1);
fp.close();
when i am running this programme first it is not displaying the content of b.txt. but when u run this prog twice then only it 'll give the correct ans. what i mean is, i'll explain that stepwise.
1. as per my prog. -- r.exec("aa.bat") -- this line 'll execute first. so content of ag 'll redirect to file "b.txt"
2. now i am trying to read the file "b.txt" using FIleInputStream...
3. but first time it is giving some garbbage value.when i give --c:jdk1.3\bin>java runbf
4. but the very next moment when again i run that file - c:jdk1.3\bin>java runbf
it 'll give the correct value.
5. again when i change the content of file ag(suppose "bbbbbbb"). & try to run "runbf.java" like this-
-- c:jdk1.3\bin>java runbf --
6. then it 'll display the value "aaaaaa". now when again i run that file
it 'll give the correct value "bbbbbb"
7. so every time i have to run that "runbf.java" twice for printing the correct
value of file "b.txt"
so what i think is that, it is not refreshing the data of file "b.txt". after executing this line
r.exec("aa.bat");
so is there any method to refresh the data of file "b.txt"??????
i think u 'll try to understand my problem...
so please help me to get the ans.......
thx.........

Answer 1

Cuz r.exec is asynchronous, dummy. Read the friggin API. It starts a background process. If you wanna wait for it to finish, then call
Process p = r.exec(...);
p.waitFor(whatever).