TryLock

Question

Hi, I am trying to run one of the example codes from the book "Horton's_Java 2", this example is trying to show us when a lock has been etablished how other attepmts will fail.
I compiled it, but when I want to run it, it throws exception and says:
Exception in thread "main" java.nio.channels.NonWritableChannelException
at sun.nio.ch.FileChannelImpl.tryLock(FileChannelImpl.java:769)
at LocingPrimesRead.main(LockingPrimesRead.java:43)
and the code is:
import java.io.*;
import java.nio.*;
import java.nio.channels.*;
public class LockingPrimesRead {
  public static void main (String[] args){
        File aFile = new File ("primes.bin");
        FileInputStream inFile = null;
        try{
            inFile = new FileInputStream(aFile);
        }catch(FileNotFoundException e){
            e.printStackTrace(System.err);
            System.exit(1);
        FileChannel inChannel = inFile.getChannel();
        final int PrimesCount = 6;
        ByteBuffer buf = ByteBuffer.allocate(8*PrimesCount);
        long[] primes = new long[PrimesCount];
        try{
            int primesRead = 0;
            FileLock inLock = null;
            while(true){
                int tryLockCount = 0;
                while(true){
                    inLock = inChannel.tryLock(inChannel.position(), buf.remaining(), false);
                    if(inLock == null){
                        if(++tryLockCount<100){
                            try{
                                Thread.sleep(200);
                            }catch(InterruptedException e){
                                e.printStackTrace(System.err);
                            continue;
                        }else{
                            System.out.println("Failed to acquire lock after " + tryLockCount+ " tries." + " Terminating...");
                            System.exit(1);
                    }else{
                            System.out.println("\nAcquired file lock.");
                            break;
                if (inChannel.read(buf) == -1) break;
                inLock.release();
                System.out.println("\nRelease file lock.");
                LongBuffer longBuf = ((ByteBuffer)(buf.flip())).asLongBuffer();
                primesRead = longBuf.remaining();
                longBuf.get(primes, 0, longBuf.remaining());
                StringBuffer str = null;
                for(int i=0; i< primesRead; i++){
                    if(i%6 ==0) System.out.println();
                    str = new StringBuffer("           ").append(primes);
System.out.print(str.substring (str.length()-12));
buf.clear();
System.out.println("\nEOF reached. ");
inFile.close();
}catch(IOException e){
e.printStackTrace(System.err);
System.exit(1);
System.exit(0);
by the way the "primes.bin" is a file which keeps some primes, if you need it I will send the code to create it later, just please let me know.
Thanks.

Answer 1

according to the api documentation this runtime exception will uccor when an attempt is made to write to a channel that was not originally opened for writing....
http://java.sun.com/j2se/1.4.1/docs/api/java/nio/channels/NonWritableChannelException.html
so, make sure that the is not read only, or maybe you have it open in someother application like notepad or something.... some applications will actually ristrict the file from being opened by other applications....
hope this helps
oaq