联合国宣布2015年为国际光与光技术年（IYL 2015）。我们开发了土耳其官方网站，并开发了三个互动小程序，帮助年轻一代了解电磁波的一些基本功能。
当我尝试从IDE运行时，applet可以运行。但是当尝试通过html代码在浏览器上运行时，每个都会出现“nullpointerexception”错误。我需要帮助来解决错误。
多普勒小程序是一个日食项目，其他是Intellij项目。我给出了源代码。
用于向网站添加applet的HTML代码示例（实际上，代码是由netbeans生成的）：
<APPLET codebase="classes" code="src/Doppler.class" width=350 height=200></APPLET>
折射 - 反射小程序：
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;
}
}
}
组和相速度小程序：
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);
}
}
多普勒效应小程序：
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();
}
}