NullPointerException stopping me from deploying. Help please?

Hey everyone,

I'm trying to deploy my program and I'm receiving this message:

Exception in thread "main" java.lang.NullPointerException
at javax.swing.ImageIcon.<init><Unknown Source>
at MiniMain.<init><MiniMain.java:36>
at MiniMain.main<MiniMain.java:14>

My program extends JFrame and also has multiple frames. The code below is just all of the code from the Class holding the Main Method. I'm quite new to Java and this is my first time trying to deploy. I believe the issue is inside the Main Method but I'm not sure. Could you please explain how to fix this?

Thanks,

Alex
Code :
import javax.swing.*;
import javax.swing.ImageIcon.*;
import java.awt.*;
import java.awt.event.*;
 
class MiniMain extends JFrame implements ActionListener {
 
final static String MAINPANEL = "Menu Panel" ; final static String ADDPANEL = "Add Panel" ;
final static String SUBPANEL = "Sub Panel" ; final static String MULPANEL = "Mul Panel" ;
final static String DIVPANEL = "Div Panel" ;
 
public static void main( String[] args ){
 
new MiniMain();
 
}
 
//JPanels And Background Info
JPanel mainPnl = new JPanel();
JPanel addPnl = new JPanel();
JPanel subPnl = new JPanel();
JPanel mulPnl = new JPanel();
JPanel divPnl = new JPanel();
JPanel backPnl = new JPanel();
JPanel scorePnl = new JPanel();
CardLayout cardlayout = new CardLayout();
JPanel cards = new JPanel( cardlayout );
JDesktopPane desk = new JDesktopPane();
 
ImageIcon backgroundImg = new ImageIcon( getClass().getResource("images/background.png") );
 
JLabel bgImg = new JLabel( backgroundImg );
 
 
//Main Page Content
ImageIcon addImage = new ImageIcon( getClass().getResource("images/buttons/addbtn.png") ); ImageIcon subImage = new ImageIcon( getClass().getResource("/images/buttons/subbtn.png") );
ImageIcon mulImage = new ImageIcon( getClass().getResource("images/buttons/mulbtn.png") ); ImageIcon divImage = new ImageIcon( getClass().getResource("/images/buttons/divbtn.png") );
 
JLabel mainLogo = new JLabel( new ImageIcon( getClass().getResource("images/mmlogo.png") ) );
JButton addBtn = new JButton( addImage );
JButton subBtn = new JButton( subImage );
JButton mulBtn = new JButton( mulImage );
JButton divBtn = new JButton( divImage );
 
//Game Page Content Went Here
 
JLabel transImg1 = new JLabel( new ImageIcon( getClass().getResource("images/transparency.png") ) ); 
JLabel transImg2 = new JLabel( new ImageIcon( getClass().getResource("images/transparency.png") ) );
JLabel transImg3 = new JLabel( new ImageIcon( getClass().getResource("images/trans2.png") ) );
JLabel transSmall = new JLabel( new ImageIcon( getClass().getResource("images/trans_small.png") ) );
 
Font mainFont = new Font( "SansSerif" , Font.PLAIN , 32 ); // Font Settings
Font scoreFont = new Font( "SansSerif" , Font.BOLD , 15 );
Color mainColour = new Color( 255 , 255 , 255 ); // White Colour For Text
 
String scoreStr; String streakStr; // For Scoring
 
private static String addQuestion;
private static String subQuestion;
private static String mulQuestion;
private static String divQuestion;
 
JTextField addAnsField = new JTextField( "" , 8 ); // Answer Fields
JTextField subAnsField = new JTextField( "" , 8 );
JTextField mulAnsField = new JTextField( "" , 8 );
JTextField divAnsField = new JTextField( "" , 8 );
 
JButton helpAdd = new JButton( helpImg ); JButton helpSub = new JButton( helpImg ); // Buttons
JButton helpMul = new JButton( helpImg ); JButton helpDiv = new JButton( helpImg );
 
JButton submitAdd = new JButton( submitImg ); JButton submitSub = new JButton( submitImg ); JButton submitMul = new JButton( submitImg ); JButton submitDiv = new JButton( submitImg );
 
JButton noteBtn = new JButton( noteImg );
JButton menuAdd = new JButton( menuImg ); JButton menuSub = new JButton( menuImg );
JButton menuMul = new JButton( menuImg ); JButton menuDiv = new JButton( menuImg );
 
public MiniMain(){
 
super( "Mini Math" );
setSize( 265 , 420 );
setDefaultCloseOperation( EXIT_ON_CLOSE );
setResizable( false );
setVisible( true );
add( mainPnl ); add( addPnl ); add( subPnl ); add( mulPnl ); add( divPnl ); add( cards ); add( backPnl );
add( scorePnl );
 
desk.add( backPnl , new Integer( 50 ) );
desk.add( cards , new Integer( 350 ) );
desk.add( scorePnl , new Integer( 400 ) );
setLayeredPane( desk );
 
 
cards.add( mainPnl , MAINPANEL );
cards.add( addPnl , ADDPANEL );
cards.add( subPnl , SUBPANEL );
cards.add( mulPnl , MULPANEL );
cards.add( divPnl , DIVPANEL );
 
 
backPnl.add( bgImg );
 
cardlayout.show( cards , MAINPANEL );
scorePnl.setVisible( false );
 
mainPnl.add( mainLogo );
mainPnl.add( transSmall );
mainPnl.add( addBtn ); mainPnl.add( subBtn );
mainPnl.add( mulBtn ); mainPnl.add( divBtn );
 
addBtn.addActionListener( this );
subBtn.addActionListener( this );
mulBtn.addActionListener( this );
divBtn.addActionListener( this );
 
}
 
 
public void plus(){
cardlayout.show( cards , ADDPANEL );
 
Numcoll.Num1() ; Numcoll.Num2();
addQuestion = Integer.toString( Numcoll.retNum1() ) + " + " + Integer.toString( Numcoll.retNum2() );
JLabel addQu = new JLabel( addQuestion );
addQu.setForeground( mainColour ); addQu.setFont( mainFont );
 
addPnl.add( whatImg );
addPnl.add( transImg1 );
addPnl.add( addQu );
addPnl.add( transImg2 );
addPnl.add( addAnsField ); addPnl.add( submitAdd );
addPnl.add( transImg3 );
addPnl.add( helpAdd ); addPnl.add( noteBtn ); addPnl.add( menuAdd );
 
submitAdd.addActionListener( this );
helpAdd.addActionListener( this );
noteBtn.addActionListener( this );
menuAdd.addActionListener( this );
 
scorePnl.setVisible( true );
scoreStr = "Score: " + Numcoll.getScore() + "    Streak: " + Numcoll.getStreak();
JLabel scoreLbl = new JLabel( scoreStr );
scorePnl.add( scoreLbl );
scoreLbl.setForeground( mainColour );
scoreLbl.setFont( scoreFont );
 
revalidate(); repaint();
}
 
public void take(){
cardlayout.show( cards , SUBPANEL );
 
Numcoll.Num1() ; Numcoll.Num2();
subQuestion = Integer.toString( Numcoll.retNum1() ) + " - " + Integer.toString( Numcoll.retNum2() );
JLabel subQu = new JLabel( subQuestion );
subQu.setForeground( mainColour ) ; subQu.setFont( mainFont );
 
subPnl.add( whatImg );
subPnl.add( transImg1 );
subPnl.add( subQu );
subPnl.add( transImg2 );
subPnl.add( subAnsField ); subPnl.add( submitSub );
subPnl.add( transImg3 );
subPnl.add( helpSub ); subPnl.add( noteBtn ); subPnl.add( menuSub );
 
submitSub.addActionListener( this );
helpSub.addActionListener( this );
noteBtn.addActionListener( this );
menuSub.addActionListener( this );
 
scorePnl.setVisible( true );
scoreStr = "Score: " + Numcoll.getScore() + "    Streak: " + Numcoll.getStreak();
JLabel scoreLbl = new JLabel( scoreStr );
scorePnl.add( scoreLbl );
scoreLbl.setForeground( mainColour );
scoreLbl.setFont( scoreFont );
 
revalidate(); repaint();
}
 
public void times(){
cardlayout.show( cards , MULPANEL );
 
Numcoll.mulNum1(); Numcoll.mulNum2();
mulQuestion = Integer.toString( Numcoll.retMul1() ) + " x " + Integer.toString( Numcoll.retMul2() ) ;
JLabel mulQu = new JLabel( mulQuestion );
mulQu.setForeground( mainColour ); mulQu.setFont( mainFont );
 
mulPnl.add( whatImg );
mulPnl.add( transImg1 );
mulPnl.add( mulQu );
mulPnl.add( transImg2 );
mulPnl.add( mulAnsField ); mulPnl.add( submitMul );
mulPnl.add( transImg3 );
mulPnl.add( helpMul ); mulPnl.add( noteBtn ); mulPnl.add( menuMul );
 
submitMul.addActionListener( this );
helpMul.addActionListener( this );
noteBtn.addActionListener( this );
menuMul.addActionListener( this );
 
scorePnl.setVisible( true );
scoreStr = "Score: " + Numcoll.getScore() + "    Streak: " + Numcoll.getStreak();
JLabel scoreLbl = new JLabel( scoreStr );
scorePnl.add( scoreLbl );
scoreLbl.setForeground( mainColour );
scoreLbl.setFont( scoreFont );
 
revalidate(); repaint();
}
 
public void divide(){
cardlayout.show( cards , DIVPANEL );
 
Numcoll.divNum1(); Numcoll.divNum2(); Numcoll.divNums();
divQuestion = Integer.toString( Numcoll.retDiv1() ) + " / " + Integer.toString( Numcoll.retDiv2() );
JLabel divQu = new JLabel( divQuestion );
divQu.setForeground( mainColour ); divQu.setFont( mainFont );
 
divPnl.add( whatImg );
divPnl.add( transImg1 );
divPnl.add( divQu );
divPnl.add( transImg2 );
divPnl.add( divAnsField ); divPnl.add( submitDiv );
divPnl.add( transImg3 );
divPnl.add( helpDiv ); divPnl.add( noteBtn ); divPnl.add( menuDiv );
 
submitDiv.addActionListener( this );
helpDiv.addActionListener( this );
noteBtn.addActionListener( this );
menuDiv.addActionListener( this );
 
scorePnl.setVisible( true );
scoreStr = "Score: " + Numcoll.getScore() + "    Streak: " + Numcoll.getStreak();
JLabel scoreLbl = new JLabel( scoreStr );
scorePnl.add( scoreLbl );
scoreLbl.setForeground( mainColour );
scoreLbl.setFont( scoreFont );
 
revalidate(); repaint();
 
}
 
 
public void actionPerformed( ActionEvent event ){
 
if( event.getSource() == addBtn ) { plus(); }
if( event.getSource() == subBtn ) { take(); }
if( event.getSource() == mulBtn ) { times(); }
if( event.getSource() == divBtn ) { divide(); }
if( event.getSource() == menuAdd ) { cardlayout.show( cards , MAINPANEL ); addPnl.remove( 2 ); scorePnl.removeAll(); Numcoll.resetStreak(); }
if( event.getSource() == menuSub ) { cardlayout.show( cards , MAINPANEL ); subPnl.remove( 2 ); scorePnl.removeAll(); Numcoll.resetStreak(); }
if( event.getSource() == menuMul ) { cardlayout.show( cards , MAINPANEL ); mulPnl.remove( 2 ); scorePnl.removeAll(); Numcoll.resetStreak(); }
if( event.getSource() == menuDiv ) { cardlayout.show( cards , MAINPANEL ); divPnl.remove( 2 ); scorePnl.removeAll(); Numcoll.resetStreak(); }
if( event.getSource() == noteBtn ) { MiniPad.pad(); return; }
if( event.getSource() == helpAdd ) { AddHelp.helpPage(); }
if( event.getSource() == helpSub ) { SubHelp.helpPage(); }
if( event.getSource() == helpMul ) { MulHelp.helpPage(); }
if( event.getSource() == helpDiv ) { DivHelp.helpPage(); }
 
if( event.getSource() == submitAdd ){
 
try{
int temp = Integer.parseInt( addAnsField.getText() ) ; Numcoll.storeAddEntered( temp );
}
catch( NumberFormatException e ) { addAnsField.setText( "" ); return; }
 
if( Numcoll.retAddEntered() == Numcoll.retAddAns() )
{ JOptionPane.showMessageDialog( this , "Next Question..." , "Correct Answer!" , JOptionPane.INFORMATION_MESSAGE ); Numcoll.addToScore( 1 ); Numcoll.addToStreak( 1 ); }
else{ JOptionPane.showMessageDialog( this , "The answer was " + Numcoll.retAddAns() + "." , "Keep Trying!" , JOptionPane.WARNING_MESSAGE ); Numcoll.resetStreak(); }
addAnsField.setText( "" );
addRestart();
 
}
 
if( event.getSource() == submitSub){
 
//similar to add
 
}
 
if( event.getSource() == submitMul){
//similar to add
 
}
 
if( event.getSource() == submitDiv){
//similar to add
}
 
 
}
 
public void addRestart() { //stuff }
public void subRestart() { //stuff }
public void mulRestart() { //stuff }
public void divRestart() { //stuff }
 
//public void showScore(){
//scorePnl.removeAll();
//scoreStr = "Score: " + Numcoll.getScore();
//
 
}