I wrote a piece of code for buffering a file - I plan on using it eventually
as part of a larger application.

However the exception handler seems to be getting called, but the getMessage
function just returns null.   I'm confused.  The file copy works fine - I
did a DOS file compare (binary) on a copied file and it seems to be working
just fine.

import java.io.*;

class XFerObject{  //read only object
long fileSize;
int blockSize; //raw bytes per packet
String fileName;
int numBlocks;
boolean isFinalBlockPartial;
long getFileSize(){
 return fileSize;
}
int getBlockSize(){
 return blockSize;
}
int getNumBlocks(){
 return numBlocks;
}
String getFileName(){
 return fileName;
}
boolean getFinalBlockPartial(){
 return isFinalBlockPartial;
}
XFerObject(XFerObject C){ //copy
 fileSize            = C.fileSize;
 blockSize           = C.blockSize;
 fileName            = C.fileName;
 numBlocks           = C.numBlocks;
 isFinalBlockPartial = C.isFinalBlockPartial;
}
XFerObject(long size, int block, String fn){
 fileSize            = size;
 blockSize           = block;
 fileName            = fn;
 isFinalBlockPartial = (fileSize%blockSize == 0? false : true);
 numBlocks           = (int)(fileSize / blockSize);
 if(isFinalBlockPartial)
  numBlocks++;
}
}

interface packetWriter{
void AcceptPacket(int PacketNumber, byte[] data) throws IOException;
}

class GNPInput{ //opens a file locally and reads
packetWriter dest;
XFerObject fileInfo;
RandomAccessFile file;
int lastBlock;
GNPInput(packetWriter d,  XFerObject f) throws IOException{
        File fileObject = new File(f.getFileName());
 file = new RandomAccessFile(fileObject, "r");
 lastBlock = 0;
 dest = d;
 fileInfo = f;
}

static long getFileSize(String f){
 File file = new File(f);
 return file.length();
}
void doXFer() throws IOException{
 byte[] packet = new byte[fileInfo.getBlockSize()];
 while(lastBlock<fileInfo.getFileSize()){
  if(lastBlock == fileInfo.getNumBlocks() -1 &&
fileInfo.getFinalBlockPartial())
   packet = new byte[(int)(fileInfo.getFileSize() %
fileInfo.getBlockSize())];
  file.seek((long)fileInfo.getBlockSize() * lastBlock);
  file.readFully(packet);
  dest.AcceptPacket(lastBlock++, packet);
 }
}
}

class GNPOutput implements packetWriter{  //creates file and writes to disk
XFerObject fileInfo;
RandomAccessFile file;
GNPOutput(XFerObject f) throws IOException{
        File fileObject = new File(f.getFileName());
 file = new RandomAccessFile(fileObject, "rw");
 file.setLength(f.getFileSize());
 fileInfo = f;
}
public void AcceptPacket(int PacketNumber, byte[] data) throws IOException{
 //System.out.println(new String(data));
 file.seek(PacketNumber * (long) fileInfo.getBlockSize());
 file.write(data);

}

}

public class gnp{

public static void main(String[] args){
 String theFile = "F:\\Documents and Settings\\Luc\\Desktop\\test";
 XFerObject myObj = new XFerObject(GNPInput.getFileSize(theFile), 3000,
theFile);
 XFerObject myObj2 = new XFerObject(GNPInput.getFileSize(theFile), 3000,
"F:\\Documents and Settings\\Luc\\Desktop\\test2out.zip");

 try{
  GNPOutput out = new GNPOutput(myObj2);
  GNPInput in = new GNPInput(out, myObj);
  in.doXFer();
 }
 catch(IOException e){
  System.out.println("oh noes!" + e.getMessage());
 }

}

}

Everything behaves as expected, the file copies - and then the output reads

oh noes!null

I cannot figure it out!

Help would be appreciated.   Is an exception actually being thrown?