How to get points of a GPX file by using GPX parser in java?

Question

import java.awt.Point;
import java.io.FileInputStream;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Date;

import javax.xml.parsers.ParserConfigurationException;

import org.alternativevision.gpx.GPXParser;
import org.alternativevision.gpx.beans.GPX;
import org.alternativevision.gpx.beans.Track;
import org.alternativevision.gpx.beans.Waypoint;
import org.xml.sax.SAXException;

public class PointParser {
 private static Double latitude;
 private static Double longitude;
 private static Double elevation;
 private static Date time;

 public static void main (String[] args) throws ParserConfigurationException, SAXException, IOException{
  FileInputStream input = new FileInputStream("E:\\sample.gpx");
  GPXParser parser = new GPXParser();
  GPX gpx = parser.parseGPX(input);
  Track trk = new Track();
  ArrayList<Waypoint> trkpt = trk.getTrackPoints();
  Object[] pointArray = trkpt.toArray();
  for (Object o : pointArray){
   Point p = (Point) o;
  }
  Waypoint wp = new Waypoint();
  latitude = wp.getLatitude();
  longitude = wp.getLongitude();
  elevation = wp.getElevation();
  time = wp.getTime();
 }
 public static Double getLatitude() {
  return latitude;
 }

 public static void setLatitude(Double latitude) {
  PointParser.latitude = latitude;
 }

 public static Double getLongitude() {
  return longitude;
 }

 public static void setLongitude(Double longitude) {
  PointParser.longitude = longitude;
 }

 public static Double getElevation() {
  return elevation;
 }

 public static void setElevation(Double elevation) {
  PointParser.elevation = elevation;
 }

 public static Date getTime() {
  return time;
 }

 public static void setTime(Date time) {
  PointParser.time = time;
 }

 
}

Hello, I'm new to java and GPXparser library. I have a GPX file which contains some track points. I want to extract 4 elements of longitude, latitude, time and elevation out of this file and use it in an algorithm in another class in my java code. when I run it I see this error:

"at PointParser.main(PointParser.java:23) Caused by: java.lang.ClassNotFoundException: org.apache.log4j.Logger"

Can anyone help me with this? Am I using GPXparser correclty?!

Thank you in advance