public void run() {
       RandomAccessFile raf = null;
       
        try {
            raf = new RandomAccessFile("file.txt", "rw");
        } catch (FileNotFoundException ex) {   }
        Random ch = new Random();
        try {

            for (int i = 0; i < Main.bytenum; i++) {
                raf.seek(raf.length());
                raf.writeChar(ch.nextInt());
                
            }
            raf.close();
			
		}
	}

ExecutorService exec = Executors.newFixedThreadPool(num);
        for (int i = 0; i < num; i++) {
            Future f1 = exec.submit(bt);
        }

	    RandomAccessFile raf = null;
        raf = new RandomAccessFile("1.txt", "rw");
        raf.setLength(length);
        raf.close();
        
        ExecutorService exec = Executors.newFixedThreadPool(num);
        for (Integer i = 1; i <= num; i++) {
            bt.setName(i.toString());
            Future f1 = exec.submit(bt);
            lst.add(f1);
			}

    public void run() {
       RandomAccessFile raf = null;
       
        try {
            raf = new RandomAccessFile("1.txt", "rw");
        } catch (FileNotFoundException ex) {
            Logger.getLogger(Main.class.getName()).log(Level.SEVERE, null, ex);
        }
        String tname = MyThread.currentThread().getName();
        tname = tname.substring(14);
        System.out.printf("#%s trying to write % d bytes\n",tname, Main.bytenum);
        
        try {
            Integer skip = Main.bytenum * (Integer.parseInt(tname)-1);
            int num = raf.skipBytes(skip);
            
            System.out.printf("#%s skipped %d bytes\n",tname, num);
            for (int i = 0; i < Main.bytenum; i++) {
                raf.write(Integer.parseInt(tname));
			}
			raf.close();
		}
	}