nullPointerException problem

[conandor]

I have this RS232 class that need to read by the main class.
Whenever i use this readData method. it throws nullPointerException message.
but if i implement it d RS232() main method, it works well with output interger value -1 or hex value 255.
why izzit like that?

Code:

/**
* @(#)RS232.java
*
* Serial Port Object
*/

import javax.comm.*;
import java.io.*;
import java.net.*;

public class RS232 {

   static InputStream in = null;
   static OutputStream out = null;

   private static RS232 instance = new RS232();
   public static RS232 getInstance() { return instance; }

   private RS232() {
 try {
  System.out.println("Connecting to serial0 at 115200bps");

  CommPortIdentifier portId = CommPortIdentifier.getPortIdentifier("serial0");
  SerialPort sp = (SerialPort)portId.open("DeviceController", 0);

         sp.setSerialPortParams(115200, SerialPort.DATABITS_8, SerialPort.STOPBITS_1, SerialPort.PARITY_NONE);
           sp.setFlowControlMode(SerialPort.FLOWCONTROL_NONE);

  sp.enableReceiveThreshold(1024);
  sp.enableReceiveTimeout(1000);

  // Get output and input stream for the serial port
  InputStream in = sp.getInputStream();
  OutputStream out = sp.getOutputStream();

/*
int data;
data = 0;
try {
  data = in.read();
  System.out.println("data");
}
catch (IOException ioe) { System.err.println("readData FAIL"); }
*/

 }
       catch (IOException ioe) {
        System.err.println("Unable to open an InputStream " + "for the serial port!");
        System.exit(1);
       }
       catch (NoSuchPortException nspe) {
        System.err.println("No Such Port");
        System.exit(2);
       }
       catch (UnsupportedCommOperationException ucoe) {
        System.err.println("Unable to set the paramets of the serial port!");
        System.exit(3);
       }
       catch (PortInUseException piue) {
        System.err.println("The serial port is in use!");
        System.exit(4);
       }
       
public int readData() {
 int data;
 data = 0;
 try {
  data = in.read();
  System.out.println("data");
 }
 catch (IOException ioe) { System.err.println("readData FAIL"); }
 return data;
}

   
  public void sendData(int b) {
       try {
  out.write((byte)b);
 }
 catch (IOException ioe) {}
   }
}

[conandor]

problem solved. pls close thread. tq