Null pointer exception i Seriel Kommunikation?

Hej jeg forsøger at få et java program til at læse fra en seriel port men det virker ikke efter hensigten.

Det detekterer godt nok min COM port som det skal men giver mig en null pointer exception.

programmet ser således ud:
package simpleread;

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

public class SimpleRead implements Runnable, SerialPortEventListener {
    static CommPortIdentifier portId;
    static Enumeration          portList;
    InputStream              inputStream;
    SerialPort              serialPort;
    Thread              readThread;

 
    public static void main(String[] args) {
    boolean              portFound = false;
    String              defaultPort = "COM3";

    if (args.length > 0) {
        defaultPort = args[0];
    }

    portList = CommPortIdentifier.getPortIdentifiers();

    while (portList.hasMoreElements()) {
        portId = (CommPortIdentifier) portList.nextElement();
        if (portId.getPortType() == CommPortIdentifier.PORT_SERIAL) {
        if (portId.getName().equals(defaultPort)) {
            System.out.println("Found port: "+defaultPort);
            portFound = true;
            SimpleRead reader = new SimpleRead();
        }
        }
    }
    if (!portFound) {
        System.out.println("port " + defaultPort + " not found.");
    }

    }

    public SimpleRead() {
    try {
        serialPort = (SerialPort) portId.open("SimpleReadApp", 10000);
    } catch (PortInUseException e) {}

    try {
        inputStream = serialPort.getInputStream();
    } catch (IOException e) {}

    try {
        serialPort.addEventListener(this);
    } catch (TooManyListenersException e) {}

    serialPort.notifyOnDataAvailable(true);

    try {
        serialPort.setSerialPortParams(9600, SerialPort.DATABITS_8,
                      SerialPort.STOPBITS_1,
                      SerialPort.PARITY_NONE);
    } catch (UnsupportedCommOperationException e) {}

    readThread = new Thread(this);

    readThread.start();
    }

   
    public void run() {
    try {
        Thread.sleep(20000);
    } catch (InterruptedException e) {}
    }

    public void serialEvent(SerialPortEvent event) {
    switch (event.getEventType()) {

    case SerialPortEvent.BI:

    case SerialPortEvent.OE:

    case SerialPortEvent.FE:

    case SerialPortEvent.PE:

    case SerialPortEvent.CD:

    case SerialPortEvent.CTS:

    case SerialPortEvent.DSR:

    case SerialPortEvent.RI:

    case SerialPortEvent.OUTPUT_BUFFER_EMPTY:
        break;

    case SerialPortEvent.DATA_AVAILABLE:
        byte[] readBuffer = new byte[20];

        try {
        while (inputStream.available() > 0) {
            int numBytes = inputStream.read(readBuffer);
        }

        System.out.print(new String(readBuffer));
        } catch (IOException e) {}

        break;
    }
    }
}



Outputtet er
run:
Found port: COM3
Exception in thread "main java.lang.NullPointerException
  at simpleread.SimpleRead <init>(SimpleRead.java:47)
  at simpleread.SimpleRead.main(SimpleRead.java:31)
BUILD SUCCESSFUL (total time 12 seconds)

linje 47 er inputStream = serialPort.getInputStream();
linje 31 er SimpleRead reader = new SimpleRead();