Action Point Of Sale Code

package cell;
import java.io.*;
abstract class CellBuffer extends CellMap
{
 private void fastRead(char[] buf) throws IOException
 {
  for (int i = 0; i<buf.length; i++)
  buf[i] = f.readChar();
  }
 private void slowWrite(char[] buf) throws IOException
 {
  int off = 0;
  if (f.getFilePointer() == 0)
  {
   off = 1;
   f.writeByte(254);
   f.writeByte(255);
   }
  for (int i = off; i<buf.length; i++)
  f.writeChar(buf[i]);
  }
 void buffer(short row, char[] buf, String op)
 {
  if (RECORD !=  buf.length) throw new IllegalArgumentException("The character buffer must have a standard length, namely "+ RECORD);
  try
  {
   goTo(row);
   if (op.equalsIgnoreCase("r"))
   fastRead(buf);
   else if (op.equalsIgnoreCase("W"))
   slowWrite(buf);
   else throw new IllegalArgumentException("Must be either R or W.");
   }
  catch (IOException e)
  {
   e.printStackTrace();
   System.exit(1);
   }
  }
 CellBuffer(String fileName)
 {
  super(fileName);
  }
 }