Exception in thread AWT-EventQueue-0 java lang NullPointerException Error

Question

Hello I m a new programmer at an high school level as a result I do not know much about programming and am getting quite a few errors which have been resolved while others I completely do not understand  I am to make a simple Check Box selection program where the user gets to pick between a variety of choices and depending on their action the image changes  The program itself compiles perfectly but when I run it however it gives me some complications  Here is my program   package components   import java awt    import java awt event    import javax swing     public class Workshop extends JPanel                       implements ItemListener   JCheckBox winterhatButton  JCheckBox sportshatButton  JCheckBox santahatButton  JCheckBox redshirtButton  JCheckBox brownshirtButton  JCheckBox suitButton  JCheckBox denimjeansButton  JCheckBox blackpantsButton  JCheckBox khakipantsButton        StringBuffer choices  JLabel pictureLabel   public Workshop         super new BorderLayout            Create the check boxes      winterhatButton   new JCheckBox  Winter Hat        winterhatButton setMnemonic KeyEvent VK Q         sportshatButton   new JCheckBox  Sports Hat        sportshatButton setMnemonic KeyEvent VK W         santahatButton   new JCheckBox  Santa hat        santahatButton setMnemonic KeyEvent VK E         redshirtButton   new JCheckBox  Red Shirt        redshirtButton setMnemonic KeyEvent VK R         brownshirtButton   new JCheckBox  Brown Shirt        brownshirtButton setMnemonic KeyEvent VK T         suitButton   new JCheckBox  Suit        suitButton setMnemonic KeyEvent VK Y         suitButton   new JCheckBox  Denim Jeans        suitButton setMnemonic KeyEvent VK U         blackpantsButton   new JCheckBox  Black Pants        blackpantsButton setMnemonic KeyEvent VK I         khakipantsButton   new JCheckBox  Khaki Pants        khakipantsButton setMnemonic KeyEvent VK O            Register a listener for the check boxes       winterhatButton addItemListener this       sportshatButton addItemListener this       santahatButton addItemListener this       redshirtButton addItemListener this       brownshirtButton addItemListener this       suitButton addItemListener this       denimjeansButton addItemListener this       blackpantsButton addItemListener this       khakipantsButton addItemListener this           Indicates     choices   new StringBuffer  ---------            Set up the picture label     pictureLabel   new JLabel        pictureLabel setFont pictureLabel getFont   deriveFont Font ITALIC        updatePicture            Put the check boxes in a column in a panel     JPanel checkPanel   new JPanel new GridLayout 0  1        checkPanel add winterhatButton       checkPanel add sportshatButton       checkPanel add santahatButton       checkPanel add redshirtButton       checkPanel add brownshirtButton       checkPanel add suitButton       checkPanel add denimjeansButton       checkPanel add blackpantsButton       checkPanel add khakipantsButton         add checkPanel  BorderLayout LINE START       add pictureLabel  BorderLayout CENTER       setBorder BorderFactory createEmptyBorder 20 20 20 20                Listens to the check boxes     public void itemStateChanged ItemEvent e        int index   0      char c    -       Object source   e getItemSelectable         if  source    winterhatButton            index   0          c    q         else if  source    sportshatButton            index   1          c    w         else if  source    santahatButton            index   2          c    e         else if  source    redshirtButton            index   3          c    r         else if  source    brownshirtButton            index   4          c    t         else if  source    suitButton            index   5          c    y         else if  source    denimjeansButton            index   6          c    u         else if  source    blackpantsButton            index   7          c    i         else if  source    khakipantsButton            index   8          c    o                if  e getStateChange      ItemEvent DESELECTED            c    -                Apply the change to the string      choices setCharAt index  c        updatePicture        protected void updatePicture           Get the icon corresponding to the image      ImageIcon icon   createImageIcon                                   images bear bear-                                    choices toString                                       gif        pictureLabel setIcon icon       pictureLabel setToolTipText choices toString         if  icon    null            pictureLabel setText  Missing Image          else           pictureLabel setText null                Returns an ImageIcon  or null if the path was invalid     protected static ImageIcon createImageIcon String path        java net URL imgURL   Workshop class getResource path       if  imgURL    null            return new ImageIcon imgURL         else           System err println  Couldn t find file      path           return null             private static void createAndShowGUI           Create and set up the window      JFrame frame   new JFrame  Build a Bear at Safeer s Workshop         frame setDefaultCloseOperation JFrame EXIT ON CLOSE          Create and set up the content pane      JComponent newContentPane   new Workshop        newContentPane setOpaque true     content panes must be opaque     frame setContentPane newContentPane          Display the window      frame pack        frame setVisible true      public static void main String   args          Schedule a job for the event-dispatching thread        creating and showing this application s GUI      javax swing SwingUtilities invokeLater new Runnable             public void run                 createAndShowGUI                            Well up to this part it runs smoothly and complies but when I proceed to run the program I get this error    gt  run components Workshop Exception in thread  AWT-EventQueue-0  java lang NullPointerException at components Workshop  lt init gt  Workshop java 75  at components Workshop createAndShowGUI Workshop java 195  at components Workshop access 0 Workshop java 189  at components Workshop 1 run Workshop java 209  at java awt event InvocationEvent dispatch Unknown Source  at java awt EventQueue dispatchEventImpl Unknown Source  at java awt EventQueue access 000 Unknown Source  at java awt EventQueue 3 run Unknown Source  at java awt EventQueue 3 run Unknown Source  at java security AccessController doPrivileged Native Method  at java security ProtectionDomain 1 doIntersectionPrivilege Unknown Source  at java awt EventQueue dispatchEvent Unknown Source  at java awt EventDispatchThread pumpOneEventForFilters Unknown Source  at java awt EventDispatchThread pumpEventsForFilter Unknown Source  at java awt EventDispatchThread pumpEventsForHierarchy Unknown Source  at java awt EventDispatchThread pumpEvents Unknown Source  at java awt EventDispatchThread pumpEvents Unknown Source  at java awt EventDispatchThread run Unknown Source    Might be a silly mistake however I cant seem to figure this out  Please Help and thank you       Here is the line that generates that error       private void jButtonSendActionPerformed java awt event ActionEvent evt                                                             TODO add your handling code here      String message      if messageBox getText   length    gt  0           message     messageBox getText            chatBox append message   n             printStream println message    this line          printStream flush              printStream close            messageBox setText

User · Answer

Near the top of the code with the Public Workshop(), I am assumeing this bit,

suitButton = new JCheckBox("Suit");
suitButton.setMnemonic(KeyEvent.VK_Y);


suitButton = new JCheckBox("Denim Jeans");
suitButton.setMnemonic(KeyEvent.VK_U);

should maybe be,

suitButton = new JCheckBox("Suit");
suitButton.setMnemonic(KeyEvent.VK_Y);


denimjeansButton = new JCheckBox("Denim Jeans");
denimjeansButton.setMnemonic(KeyEvent.VK_U);

User · Answer

NullPointerExceptions are  among the easier exceptions to diagnose  frequently  Whenever you get an exception in Java and you see the stack trace   that s what your second quote-block is called  by the way    you read from top to bottom  Often  you will see exceptions that start in Java library code or in native implementations methods  for diagnosis you can just skip past those until you see a code file that you wrote   Then you like at the line indicated and look at each of the objects   instantiated classes   on that line -- one of them was not created and you tried to use it  You can start by looking up in your code to see if you called the constructor on that object  If you didn t  then that s your problem  you need to instantiate that object by calling new Classname  arguments    Another frequent cause of NullPointerExceptions is accidentally declaring an object with local scope when there is an instance variable with the same name   In your case  the exception occurred in your constructor for Workshop on line 75   lt init gt  means the constructor for a class  If you look on that line in your code  you ll see the line   denimjeansButton addItemListener this     There are fairly clearly two objects on this line  denimjeansButton and this  this is synonymous with the class instance you are currently in and you re in the constructor  so it can t be this  denimjeansButton is your culprit  You never instantiated that object  Either remove the reference to the instance variable denimjeansButton or instantiate it

[nullpointerexception] Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException Error

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