Aide exception sur netbeans

salut tous le monde,s'il vous plais est ce que quelqu'un peut m'aider.dans le cadre de mon projet de fin d'étude j'ai besoin de lire les données issus d'un port COM.ces données sont celles des trois capteurs.je fais un classe SimpleRead qui permet la lecture des données et ça marche bien.dans une interface final j'ai besoin que lorsque je clique sur une bouton en netbeans je fais l'appel à ce programme il m'affiche le message suivant:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at projet1.SimpleRead.<init>(SimpleRead.java:44)
at projet1.FENETREFINAL.jButton4ActionPerformed(FENETREFINAL.java:229)
at projet1.FENETREFINAL.access$300(FENETREFINAL.java:28)
at projet1.FENETREFINAL$4.actionPerformed(FENETREFINAL.java:99)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
at java.awt.AWTEventMulticaster.mouseReleased(AWTEventMulticaster.java:272)
at java.awt.Component.processMouseEvent(Component.java:6267)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3267)
at java.awt.Component.processEvent(Component.java:6032)
at java.awt.Container.processEvent(Container.java:2041)
at java.awt.Component.dispatchEventImpl(Component.java:4630)
at java.awt.Container.dispatchEventImpl(Container.java:2099)
at java.awt.Component.dispatchEvent(Component.java:4460)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4577)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4238)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4168)
at java.awt.Container.dispatchEventImpl(Container.java:2085)
at java.awt.Window.dispatchEventImpl(Window.java:2478)
at java.awt.Component.dispatchEvent(Component.java:4460)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)
//programme qui permet la lecture de port
package projet1;

/**
*
* @author user
*/
import java.io.*;
import java.util.*;
import javax.comm.*;
import com.sun.comm.Win32Driver;
import com.sun.comm.Win32Driver;

public class SimpleRead implements Runnable, SerialPortEventListener {
static CommPortIdentifier portId;
static Enumeration portList;

InputStream inputStream;
SerialPort serialPort;
Thread readThread;

public static void main(String[] args) {
portList = CommPortIdentifier.getPortIdentifiers();

while (portList.hasMoreElements()) {
portId = (CommPortIdentifier) portList.nextElement();
if (portId.getPortType() == CommPortIdentifier.PORT_SERIAL) {
if (portId.getName().equals("COM4")) {
// if (portId.getName().equals("/dev/term/a")) {
SimpleRead reader = new SimpleRead();
}
}
}
}

public SimpleRead() {
for(int i=0;i<3;i++)
{
try {
serialPort = (SerialPort) portId.open("SimpleReadApp", 2000);
} catch (PortInUseException e) {System.out.println(e);}
try {
inputStream = serialPort.getInputStream();
} catch (IOException e) {System.out.println(e);}
try {
serialPort.addEventListener(this);
} catch (TooManyListenersException e) {System.out.println(e);}
serialPort.notifyOnDataAvailable(true);
try {
serialPort.setSerialPortParams(38400,
SerialPort.DATABITS_8,
SerialPort.STOPBITS_1,
SerialPort.PARITY_NONE);
} catch (UnsupportedCommOperationException e) {System.out.println(e);}
readThread = new Thread(this);
readThread.start();
}
}
public void run() {
try {
Thread.sleep(10);
} catch (InterruptedException e) {System.out.println(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) {System.out.println(e);}
break;
}
}
}
//mon interface final
private void jButton4ActionPerformed(java.awt.event.ActionEvent evt) {
// TODO add your handling code here:
this.getName().equals("COM4");
SimpleRead s=new SimpleRead();
s.readThread.start();
s.run();

//s.serialEvent(null);

}
merci pour votre aide