Applet nullpointerexception and help for a scientific project

Question

UN proclaimed 2015 as the International Year of Light and Light-based Technologies (IYL 2015). We have developed the Turkey official web site and also devolop three interactive applet that help young generation to understand some basic fundementals of electromagnetic waves.

The applets can run when i try to run from IDEs. But each of them gives "nullpointerexception" error when try to run at browser by html codes. I need help to solve the error.

Doppler applet is an eclipse project, the others are Intellij projects. I give the source code blow.

HTML Code sample that i use to add applets to web site (actually, the code is orginally generated by netbeans):

<APPLET codebase="classes" code="src/Doppler.class" width=350 height=200></APPLET>

Refraction-Reflection Applet:

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Vector;
import javax.swing.JApplet;
import javax.swing.JButton;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;
public class Refraction extends JApplet implements ActionListener {

int finPoint=200;
int upperLineFinx=finPoint;
int upperLineFiny=finPoint;
int bottomLineBegx=upperLineFinx;
int bottomLineBegy=upperLineFiny;
int lengthOfLines=150;
double teta1=50*Math.PI/180;
double n1=1;
double n2= 1;
double teta2= Math.asin((n1 / n2) * Math.sin(teta1)) ;
double temp;
static final int angle_min = 0;
static final int angle_max = 90;
static final int angle_rate = 15;
Vector model1=new Vector();
Vector model2=new Vector();
JSlider angle_slider;
JComboBox n1ComboBox,n2ComboBox;
JButton button1;
JTextField incidenceTF,refractionTF,n1TF,n2TF;
JLabel yan_kir_lab;
Graphics bufferGraphics;
Image offImg;
Dimension dim,dimSlider;

public Refraction(){
    model1.addElement(new Item(1,"Hava"));
    model1.addElement(new Item(1.309,"Buz"));
    model1.addElement(new Item(1.333,"Su"));
    model1.addElement(new Item(1.36,"Ethanol"));
    model1.addElement(new Item(1.47,"Zeytin Yağı"));
    model1.addElement(new Item(1.48,"Cam"));
    model1.addElement(new Item(2.42,"Elmas"));

    button1=new JButton("Değiştir");
    n1ComboBox=new JComboBox(model1);
    n2ComboBox=new JComboBox(model1);
}

public void init(){
    incidenceTF=new JTextField(String.valueOf(teta1/Math.PI*180));
    refractionTF=new JTextField(String.valueOf(teta2/Math.PI*180));
    n1TF=new JTextField(String.valueOf(n1));
    n2TF=new JTextField(String.valueOf(n2));
    yan_kir_lab=new JLabel(" Kırılma Açısı=");
    dim= new Dimension(600, 400);
    this.setSize(dim);
    setBackground(Color.white);
    setLayout(new BorderLayout());
    Panel p1=new Panel();
    Panel p2=new Panel();
    Panel p3=new Panel();
    p1.setBackground(new Color(0xEBE669));
    p1.setLayout(new GridLayout(10, 0));
    addLabel(" Aci", p1);
    addSlider(p1);
    addnCombobox(n1ComboBox, 1, p1);
    addnCombobox(n2ComboBox,2,p1);
    p1.add(new Label());
    p2.setBackground(new Color(0xEBE669));
    p2.setSize(new Dimension(200, 200));
    p2.setLayout(new GridLayout(2, 2));
    p2.add(new JLabel(" Gelme Açısı="));
    p2.add(incidenceTF);
    p2.add(yan_kir_lab);
    p2.add(refractionTF);
    p1.add(p2);
    p3.setBackground(new Color(0xEBE669));
    p3.setSize(new Dimension(200, 200));
    p3.setLayout(new GridLayout(2, 2));
    p3.add(new JLabel(" n1="));
    p3.add(n1TF);
    p3.add(new JLabel(" n2="));
    p3.add(n2TF);
    p1.add(p3);
    add(p1, BorderLayout.EAST);
    offImg=createImage(dim.width,dim.height);
    bufferGraphics=offImg.getGraphics();
    angle_slider.addChangeListener(new ChangeListener() {
        @Override
        public void stateChanged(ChangeEvent e) {
            teta1=(((JSlider) e.getSource()).getValue())*Math.PI/180;
            temp=(n1 / n2) * Math.sin(teta1);
            //Math.asin((n1 / n2) * Math.sin(teta1 * Math.PI / 180.0))
            if(temp>=1){
                teta2 = teta1;
                yan_kir_lab.setText(" Yansıma Açısı=");
            }
            else{ teta2 = Math.asin(temp);
                  yan_kir_lab.setText(" Kırılma Açısı=");
            }
            String teta1tostring=String.valueOf(teta1/Math.PI*180);
            String teta2tostring=String.valueOf(teta2/Math.PI*180);
            if(teta1tostring.length()>5) teta1tostring=teta1tostring.substring(0,5);
            if (teta2tostring.length()>5) teta2tostring=teta2tostring.substring(0,5);
            incidenceTF.setText(teta1tostring);
            refractionTF.setText(teta2tostring);
            repaint();
        }
    });
    this.setVisible(true);

}
public void actionPerformed(ActionEvent e) {



    if(e.getSource()==n1ComboBox){
        Item item1 = (Item) n1ComboBox.getSelectedItem();
        n1 = item1.getValue();
        repaint();
    }
    else if (e.getSource()==n2ComboBox){
        Item item2=(Item) n2ComboBox.getSelectedItem();
        n2=item2.getValue();
        repaint();
    }

    repaint();
}

public void addLabel( String text ,Container cont){
    JLabel label=new JLabel();
    label.setText(text);
    cont.add(label);
}

public void addSlider(Container conteiner){
    angle_slider=new JSlider(JSlider.HORIZONTAL,angle_min,angle_max,angle_rate);
    dimSlider=new Dimension(200,40);
    angle_slider.setValue((int)(teta1*180/Math.PI));
    angle_slider.setBackground(new Color(0xEBE669));
    angle_slider.setMajorTickSpacing(15);
    angle_slider.setMinorTickSpacing(5);
    angle_slider.setPaintLabels(true);
    angle_slider.setPreferredSize(dimSlider);
    angle_slider.setAlignmentX(Component.RIGHT_ALIGNMENT);
    angle_slider.setVisible(true);
    conteiner.add(angle_slider);
}
public void addnCombobox(JComboBox cb, final int whichComboBox,Container cont){

    cb.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            if(whichComboBox==1){
                Item item1 = (Item) n1ComboBox.getSelectedItem();
                n1 = item1.getValue();
                n1TF.setText(String.valueOf(n1));
                repaint();
            }
            else if (whichComboBox==2){
                Item item2=(Item) n2ComboBox.getSelectedItem();
                n2=item2.getValue();
                n2TF.setText(String.valueOf(n2));
                repaint();
            }
        }
    });
    cont.add(cb);
}

public void paint (Graphics g) {


    bufferGraphics.clearRect(0, 0, dim.width, dim.height);
    bufferGraphics.setColor(Color.white);

    bufferGraphics.setColor(new Color(0xB1EFEE));
    bufferGraphics.fillRect(0, 200, 400, 400);

    bufferGraphics.setColor(Color.red);
    bufferGraphics.drawLine(200,0,200,400);
    bufferGraphics.drawLine(0,200,400,200);

    bufferGraphics.setColor(Color.black);
    bufferGraphics.drawLine((int)(200-lengthOfLines*Math.sin(teta1)),(int)(200-lengthOfLines*Math.cos(teta1)),upperLineFinx,upperLineFiny);


    if(temp>=1){
        bufferGraphics.drawLine(bottomLineBegx,bottomLineBegy,(int)(200+lengthOfLines*Math.sin(teta2)),(int)(200-lengthOfLines*Math.cos(teta2)));
    }
    else {
        bufferGraphics.drawLine(bottomLineBegx, bottomLineBegy, (int) (200 + lengthOfLines * Math.sin(teta2)), (int) (200 + lengthOfLines * Math.cos(teta2)));
    }
    g.drawImage(offImg,0,0,this);
}
public void update(Graphics g)
{
    paint(g);
}




class Item
{
    private double value;
    private String description;

    public Item(double value, String description)
    {
        this.value = value;
        this.description = description;
    }

    public double getValue()
    {
        return value;
    }

    public String getDescription()
    {
        return description;
    }

    public String toString()
    {
        return description;
    }
}

}

Group and Phase Velocity Applet:

import javafx.scene.control.Slider;
import javax.swing.*;
import javax.swing.border.Border;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.BasicStroke;
import java.awt.Graphics2D;


public class GrupVeFazHizi extends JApplet implements ActionListener {

Timer timer= new Timer(30,this);
Graphics2D bufferGraphics;
Image offImg;
Dimension dim;
int[] xs;
int[] ys,ys2,ys3;
int pixelNumber=600;
int yBase=120;
double t;
int waveAmp=100;
private double k=0.3;
int phaseVel=20;
double groupVel=phaseVel*1.4;
double L=50;
boolean repeatCheck;
Dimension sliderDim,labelDim;
Border b = BorderFactory.createLineBorder( new Color(0x96937E), 1 );
JSlider groupVelSlider=new JSlider(JSlider.HORIZONTAL,0,100,1);
JSlider phaseVelSlider=new JSlider(JSlider.HORIZONTAL,0,100,1);
JSlider waveAmpSlider=new JSlider(JSlider.HORIZONTAL,0,150,1);
JSlider kSlider=new JSlider(JSlider.HORIZONTAL,0,10,1);
JSlider lSlider=new JSlider(JSlider.HORIZONTAL,0,100,1);


Label grupHiziLabel=new Label("            Grup Hızı");
public void init(){
    xs=new int[pixelNumber];
    ys=new int[pixelNumber];
    ys2=new int[pixelNumber];
    ys3=new int[pixelNumber];
    labelDim=new Dimension(50,50);
    grupHiziLabel.setPreferredSize(labelDim);
    prepareSliders();

    repeatCheck=false;
    t=0.01;
    dim=new Dimension(600,400);
    this.setSize(dim);
    setBackground(Color.white);
    offImg=createImage(dim.width,dim.height);
    bufferGraphics=(Graphics2D) offImg.getGraphics();
    setLayout(new BorderLayout());
    Panel p1= new Panel();
    p1.setSize(new Dimension(200,200));
    p1.setBackground(new Color(0xFF9C7C));
    p1.setLayout(new GridLayout(2, 5));
    //p1.add(new Label("Grup Hızı"));
    p1.add(grupHiziLabel);
    p1.add(new Label("             Faz Hızı"));
    p1.add(new Label("       Dalga Genliği"));
    p1.add(new Label("     Dalga Sayısı*10"));
    p1.add(new Label("        Dalga Boyu"));
    addSlider(groupVelSlider, p1);
    addSlider(phaseVelSlider, p1);
    addSlider(waveAmpSlider, p1);
    addSlider(kSlider, p1);
    addSlider(lSlider,p1);
    add(p1, BorderLayout.SOUTH);
    timer.setRepeats(true);
    timer.start();
    for(int i=0;i<pixelNumber;i++){
        xs[i]=i;
        ys[i]=yBase;
        ys2[i]=yBase;
        ys3[i]=yBase;
    }
}
public void paint (Graphics g){
    bufferGraphics.clearRect(0,0,dim.width,dim.height);
    bufferGraphics.setColor(Color.white);
    bufferGraphics.setStroke(new BasicStroke(1.0f));

    bufferGraphics.setColor(Color.black);
    bufferGraphics.drawPolyline(xs, ys, pixelNumber);
    bufferGraphics.setColor(Color.red);
    bufferGraphics.setStroke(new BasicStroke(2.0f));
    bufferGraphics.drawPolyline(xs,ys2,pixelNumber);
    bufferGraphics.drawPolyline(xs,ys3,pixelNumber);
    g.drawImage(offImg,0,0,this);
}
public void update(Graphics g)
{
    paint(g);
}
@Override
public void actionPerformed(ActionEvent e) {
    for(int i=0;i<pixelNumber;i++){
        ys[i]=yBase+(int) (waveAmp*(Math.exp(-Math.pow((((xs[i]+110)-groupVel*t)/L),2))* Math.cos(k*(xs[i]-phaseVel*t))));
        ys2[i]=yBase+(int)(waveAmp*Math.exp(-Math.pow((((xs[i]+110)-groupVel*t)/L),2)));
        ys3[i]=yBase+(int)(-waveAmp*Math.exp(-Math.pow((((xs[i]+110)-groupVel*t)/L),2)));
    }
    if(ys2[pixelNumber-1]>yBase+2){
        repeatCheck=true;
    }
    if(repeatCheck==true && ys2[pixelNumber-1]<=(yBase)){
        repeatCheck=false;
        t=0.01;
    }
    t=t+0.05;
    repaint();
}
public void addSlider(final JSlider slider,Container container){
    slider.setPreferredSize(new Dimension(100,20));
    slider.setAlignmentX(Component.LEFT_ALIGNMENT);
    slider.setBackground(new Color(0xF5FF9B));
    slider.setBorder(b);
    slider.setVisible(true);
    slider.addChangeListener(new ChangeListener() {
        @Override
        public void stateChanged(ChangeEvent e) {
            if(slider==groupVelSlider)             groupVel=slider.getValue();
            else if (slider==phaseVelSlider)       phaseVel=slider.getValue();
            else if (slider==waveAmpSlider)        waveAmp=waveAmpSlider.getValue();
            else if (slider==kSlider)              k=kSlider.getValue()/10.0;
            else                                   L=lSlider.getValue();
            repaint();
        }
    });
    container.add(slider);
}
private void prepareSliders(){
    sliderDim=new Dimension(150,40);
    groupVelSlider.setPreferredSize(sliderDim);
    phaseVelSlider.setPreferredSize(sliderDim);
    waveAmpSlider.setPreferredSize(sliderDim);
    kSlider.setPreferredSize(sliderDim);
    lSlider.setPreferredSize(sliderDim);

    groupVelSlider.setValue((int) groupVel);
    phaseVelSlider.setValue(phaseVel);
    waveAmpSlider.setValue(waveAmp);
    kSlider.setValue((int) (k*10));
    lSlider.setValue((int) L);

    groupVelSlider.setMajorTickSpacing(50);
    phaseVelSlider.setMajorTickSpacing(50);
    waveAmpSlider.setMajorTickSpacing(75);
    kSlider.setMajorTickSpacing(5);
    lSlider.setMajorTickSpacing(50);

    groupVelSlider.setPaintLabels(true);
    phaseVelSlider.setPaintLabels(true);
    waveAmpSlider.setPaintLabels(true);
    kSlider.setPaintLabels(true);
    lSlider.setPaintLabels(true);
}
}

Doppler Effect Applet:

package Doppler;

import javax.imageio.ImageIO;
import javax.swing.*;
import javax.swing.border.Border;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;
import java.applet.AppletContext;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.IOException;
import java.net.URL;
import java.awt.BasicStroke;
import java.awt.Graphics2D;



public class Doppler extends JApplet implements ActionListener {

Graphics2D bufferGraphics;
Image offImg;
Dimension dim;
Timer timer= new Timer(30,this);
int waveVelocity=3;
int waveNumber=1000;
int waveFrequency=30;
int frequencyCheck=0;
int maxFrequency=60;
Circle[] circles = new Circle[waveNumber];
AmbulanceObj amb=new AmbulanceObj();
Image ambulanceImage,buildings, ground;
AppletContext context;
int circleNumber=waveNumber;
private int sayac;
Label ambVelLabel,waveVelLabel,frequencyLabel;
JSlider ambVelSlider=new JSlider(0,5,1);
JSlider waveVelSlider=new JSlider(0,5,1);
JSlider frequencySlider=new JSlider(1,maxFrequency,1);
Border b = BorderFactory.createLineBorder( new Color(0x96937E), 1 );





public class Circle {
    int centx=0;
    int centy=0;
    int radiusx=0;
    int radiusy=0;
    int velocity=0;
    public Circle(int x,int y, int radx,int rady, int vel){
        this.centx=x;
        this.centy=y;
        this.radiusx=radx;
        this.radiusy=rady;
        this.velocity=vel;
    }
    public Circle(int x,int y) {
        this.centx = x;
        this.centy = y;
    }
}
public class AmbulanceObj{
    int ambX=0;
    int ambY=255;
    int ambWidth=50;
    int ambHeight=20;
    int ambVelocity=1;
}
public void addSlider(final JSlider slider,Container container){
    slider.setPreferredSize(new Dimension(100,20));
    slider.setAlignmentX(Component.LEFT_ALIGNMENT);
    slider.setBackground(new Color(0xF5FF9B));
    slider.setBorder(b);
    slider.setVisible(true);
    slider.addChangeListener(new ChangeListener() {
        @Override
        public void stateChanged(ChangeEvent e) {
            if(slider==ambVelSlider) amb.ambVelocity=ambVelSlider.getValue();
            else if(slider==waveVelSlider) waveVelocity=waveVelSlider.getValue();
            else if (slider==frequencySlider) waveFrequency=maxFrequency-frequencySlider.getValue()+1;
            repaint();
        }
    });
    container.add(slider);
}
public Image getImage(String name)
{
    URL imgUrl = getClass().getClassLoader().getResource("resources/"+name);
    ImageIcon icon = new ImageIcon(imgUrl);
    return icon.getImage();
}

public void init(){
    amb.ambX=-20;
    ambVelLabel=new Label("   Ambulans Hızı:");
    waveVelLabel=new Label("     Dalga Hızı:");
    frequencyLabel=new Label("      Frekans:");
    ambVelSlider.setValue(amb.ambVelocity);
    waveVelSlider.setValue(waveVelocity);
    frequencySlider.setValue(maxFrequency-waveFrequency+1);
    ambulanceImage= getImage("ambulance1.png");
    buildings= getImage("rsz_building3.png");
    ground= getImage("rsz_3ground.png");

    for (int i=0;i<circleNumber;i++){
        circles[i]=new Circle(amb.ambX+amb.ambWidth,amb.ambY);
        circles[i].velocity=0;
    }

    dim= new Dimension(600,400);
    this.setSize(dim);
    setBackground(new Color(0xD4FFFC));
    setLayout(new BorderLayout());
    Panel p1= new Panel();
    p1.setSize(new Dimension(600,20));
    p1.setBackground(new Color(0xEBE669));
    p1.setLayout(new GridLayout(0, 6));
    p1.add(ambVelLabel);
    addSlider(ambVelSlider,p1);
    p1.add(waveVelLabel);
    addSlider(waveVelSlider,p1);
    p1.add(frequencyLabel);
    addSlider(frequencySlider,p1);
    add(p1, BorderLayout.SOUTH);

    offImg=createImage(dim.width,dim.height);
    bufferGraphics=(Graphics2D) offImg.getGraphics();
    sayac=0;
    timer.setRepeats(true);
    timer.start();

}

public void paint( Graphics g){

    bufferGraphics.clearRect(0,0,dim.width,dim.height);
    bufferGraphics.drawImage(buildings,0,0,this);
    bufferGraphics.drawImage(ambulanceImage,amb.ambX,amb.ambY,this);
    bufferGraphics.setColor(new Color(0xBF3002));
    bufferGraphics.setStroke(new BasicStroke(2.0f));
    for(int a=0;a<waveNumber;a++) {
        bufferGraphics.drawOval(circles[a].centx - (circles[a].radiusx / 2), circles[a].centy - (circles[a].radiusy / 2), circles[a].radiusx, circles[a].radiusy);
    }
    bufferGraphics.setStroke(new BasicStroke(1.0f));
    bufferGraphics.drawImage(ground,0,300,this);
    g.drawImage(offImg,0,0,this);
}
public void update(Graphics g)
{
    paint(g);
}

@Override
public void actionPerformed(ActionEvent e) {
    amb.ambX+=amb.ambVelocity;
    if((frequencyCheck% (double) waveFrequency==0 && amb.ambX+amb.ambWidth<600) ){
        circles[sayac].centx=amb.ambX+amb.ambWidth;
        circles[sayac].centy=amb.ambY+10;
        circles[sayac].velocity=waveVelocity;
        sayac+=1;
    }


    else if(amb.ambX+amb.ambWidth>=600 || circles[waveNumber-1].velocity>0){
        amb.ambX=-20;
        for (int i=0;i<circleNumber;i++){
            circles[i]=new Circle(amb.ambX+amb.ambWidth,amb.ambY);
            circles[i].velocity=0;
        }
        sayac=0;
        frequencyCheck=0;
    }
    for(int a=0;a<waveNumber;a++){
        circles[a].radiusx+=circles[a].velocity;
        circles[a].radiusy+=circles[a].velocity;
    }
    frequencyCheck=frequencyCheck+1;
    repaint();
}
}