GSM Java

import com.pi4j.io.serial.Serial;
import com.pi4j.io.serial.SerialDataEvent;
import com.pi4j.io.serial.SerialDataListener;
import com.pi4j.io.serial.SerialFactory;
import com.pi4j.io.serial.SerialPortException;

public class Main extends Thread {
    public static Serial serial;


    public static void main(String args[]) throws InterruptedException {
        serial = SerialFactory.createInstance();

        serial.addListener(new SerialDataListener() {

            @Override
            public void dataReceived(SerialDataEvent arg0) {
                System.out.print(arg0.getData());

            }

        });

        try {
            serial.open(Serial.DEFAULT_COM_PORT, 9600);
            Thread.sleep(1000);
            for(;;) {
                try {
                    System.out.println("AT");
                    serial.write("AT\r");
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }

        } catch(SerialPortException ex) {
            ex.printStackTrace();
            return;
        }
    }
}