I'm currently working on a college Hangman project to build a GUI to ply an external hangman game, but I keep recieving a NullPointerException error. Here is the code for the GUI

import java.awt.BorderLayout;
import java.awt.GridLayout;
import java.awt.Color;
import java.awt.Image;
import java.awt.Graphics;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import java.awt.Font;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JLabel;
import javax.swing.JTextField;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;
import javax.swing.ButtonGroup;
import javax.swing.JRadioButtonMenuItem;
import javax.swing.ImageIcon;

public class HangmanFrame extends JFrame
{
    private JTextField wordField;
    private JTextField livesField;

    private static final int FRAME_WIDTH = 650;
    private static final int FRAME_HEIGHT = 550;

    private JButton newButton;  
    private JButton quitButton; 

    private JButton[] alphaButton;

    private char[] names;

    private JPanel containerPanel;
    private JPanel northPanel;
    private JPanel southPanel;
    private JPanel westPanel;
    private JPanel centrePanel;

    private JLabel imageLabel;

    private HangmanGame game;
    private WordGenerator myWord;


    private Font buttonFont = new Font("Bradley Hand ITC",Font.BOLD, 18);
    private Font largeFont = new Font("Bradley Hand ITC",Font.BOLD, 24);

    public HangmanFrame()
   {
        setSize(FRAME_WIDTH, FRAME_HEIGHT);
        containerPanel = new JPanel();
        WordGenerator myWord = new WordGenerator();
        HangmanGame game = new HangmanGame(myWord.getWord());

        createWordField();
        createImagePanel();
        createLetterPanel();
        createButtonPanel();
        createContainerPanel();
        createMenuBar();
    }   

    public void createMenuBar()
    {
        JMenuBar menuBar = new JMenuBar();
        setJMenuBar(menuBar);

        JMenu fileMenu = new JMenu("File");
        JMenu levelMenu = new JMenu("Level");
        menuBar.add(fileMenu);
        menuBar.add(levelMenu);

        JMenuItem exitAction = new JMenuItem("Exit");

        JRadioButtonMenuItem EasyRB = new JRadioButtonMenuItem("Easy");
        JRadioButtonMenuItem HardRB = new JRadioButtonMenuItem("Hard");

        ButtonGroup bg = new ButtonGroup();
         bg.add(EasyRB);
        bg.add(HardRB);

        levelMenu.add(EasyRB);
        levelMenu.add(HardRB);

        fileMenu.add(exitAction);       
    }


    public JPanel createContainerPanel()
    {
        containerPanel.setLayout(new BorderLayout());   

        containerPanel.add(createWordField(), BorderLayout.NORTH);
        containerPanel.add(createImagePanel(), BorderLayout.WEST);  
        containerPanel.add(createLetterPanel(), BorderLayout.CENTER);
        containerPanel.add(createButtonPanel(), BorderLayout.SOUTH);

        add(containerPanel);    

        return containerPanel;  
    }   

    public JTextField createWordField()
    {
        wordField = new JTextField(10);

        wordField.setHorizontalAlignment(JTextField.CENTER);
        wordField.setEditable(false);
        wordField.setBackground(Color.black);
        wordField.setForeground(Color.white);
        wordField.setBorder(null);

        JPanel northPanel = new JPanel();
        northPanel.add(wordField);
        northPanel.setBackground(Color.black);

        wordField.setFont(largeFont);

        return wordField;
    }

    public Image getImage(String path)
    { 
        Image image = null; 
        return image; 
    }


    public JPanel createImagePanel()
    {
        JPanel westPanel = new JPanel(new BorderLayout());

        ImageIcon image = new ImageIcon("background.jpg"); 
        JLabel imageLabel = new JLabel(image);

        westPanel.setBackground(Color.black);

        JTextField livesField = new JTextField();
        livesField.setBackground(Color.black);
        livesField.setForeground(Color.white);
        livesField.setFont(buttonFont);
        livesField.setBorder(null); 

        westPanel.add(imageLabel,BorderLayout.CENTER);
        westPanel.add(livesField,BorderLayout.SOUTH);

        return westPanel;   
    }

    public JPanel createLetterPanel()
    {
        JPanel centrePanel = new JPanel();
        centrePanel.setLayout(new GridLayout(5, 5));
        centrePanel.setBackground(Color.black);     

        final JButton alphaButton[]=new JButton[26];

        String alpha = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

        for (int i = 0; i <alphaButton.length; i++) 
        { 
            String letter = "" + alpha.charAt(i);
            alphaButton[i]= new JButton(letter);

            centrePanel.add(alphaButton[i]); 

            alphaButton[i].setOpaque(false); 
            alphaButton[i].setContentAreaFilled(false); 
            alphaButton[i].setBorderPainted(false);
            alphaButton[i].setEnabled(false);

            alphaButton[i].setFont(buttonFont);
            alphaButton[i].setForeground(Color.white);

            ActionListener listener = new ButtonListener();
            alphaButton[i].addActionListener(listener);

        }
        return centrePanel;
    }

    class ButtonListener implements ActionListener
    {   
        public void actionPerformed(ActionEvent e)
       {        
            String label = e.getActionCommand();
            JButton button = (JButton)e.getSource();
            game.guessLetter(label.charAt(0));
            wordField.setText(game.showDashes());   
            livesField.setText("      "+game.getLives());
            button.setEnabled(false);
            button.setVisible(false);               
        }
    }

    public JPanel createButtonPanel()
    {   
        JPanel southPanel = new JPanel();
        southPanel.setLayout(new GridLayout(1, 2));
        southPanel.setBackground(Color.black);

        newButton = new JButton("New Game");

        newButton.setOpaque(false); 
        newButton.setContentAreaFilled(false); 
        newButton.setBorderPainted(false);
        newButton.setFont(buttonFont);
        newButton.setForeground(Color.white);
        ActionListener newListener = new NewButtonListener();
        newButton.addActionListener(newListener);

        quitButton = new JButton("Quit");

        quitButton.setOpaque(false); 
        quitButton.setContentAreaFilled(false); 
        quitButton.setBorderPainted(false);;
        quitButton.setFont(buttonFont);
        quitButton.setForeground(Color.white);
        ActionListener quitListener = new QuitButtonListener();
        quitButton.addActionListener(quitListener);

        southPanel.add(newButton);
        southPanel.add(quitButton);

        return southPanel;      
    }

    class NewButtonListener implements ActionListener
    {   
        public void actionPerformed(ActionEvent f)
       {    
            wordField.setText(game.showDashes());   

            livesField.setText("      "+game.getLives());

            for (int i=0; i<26; i++)
            {
                alphaButton[i].setEnabled(true);    
            }       
        }
    }

    class QuitButtonListener implements ActionListener
    {
        public void actionPerformed(ActionEvent g)
      {
        System.exit(0);      
        }
   }

}

Here is the external game I am tryin to import:

public class HangmanGame
{

    private String secretWord;
    private char[] dashes;
    private int lives; 

    //constructor
    //sets secretWord
    //creates and initialises dashes with correct no of dashes
    //sets lives to default value 8
    public HangmanGame(String wordIn)
    {
        secretWord = wordIn;
        dashes = new char[secretWord.length()];
        fillDashes();
        lives = 8;  //default
    }


    //checks if letter guessed is in secretword
    //if it is - puts letter in correct location in dashes[]
    //else lose a life
    public void guessLetter(char letterIn)
    {
        boolean found = false;
        for(int i = 0; i<secretWord.length(); i++)
        {
            if(letterIn == secretWord.charAt(i)){
                dashes[i] = letterIn;
                found = true;
            }

        }
        if(!found)
            lives--;

    }

    //returns true when game over - correct word guessed or 0 lives left
    //otherwise returns false
    public boolean gameOver()
    {
        if(secretWord.equalsIgnoreCase(showDashes()) || lives == 0)
            return true;
        else 
            return false;

        //return secretWord.equalsIgnoreCase(showDashes()) || lives == 0;

    }

    //returns the secretword
    public String showSecretWord()
    {
        return secretWord;
    }

    //method to show the chars in dashes - 
    //returns a string made up of either dashes or correct letter
    public String showDashes()
    {
        String s ="";
        for(int i = 0; i< dashes.length; i++)
            s +=dashes[i];

        return s;
    }

    //method initialises  dashes[] with dashes at start of game
    public void fillDashes()
    {
        for(int i = 0; i< dashes.length; i++)
        dashes[i]='-';      
    }

    //returns the num of lives left
    public int getLives()
    {
        return lives;
    }

    //sets the number of lives
    public void setLives(int livesIn)
    {
        lives = livesIn;
    }
}

I am using a seperate viewer to view the game, but each time I click on new game i am getting the following error:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at HangmanFrame$NewButtonListener.actionPerformed(HangmanFrame.java:246)
    at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2028)
    at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2351)
    at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
    at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
    at java.awt.Component.processMouseEvent(Component.java:6382)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3275)
    at java.awt.Component.processEvent(Component.java:6147)
    at java.awt.Container.processEvent(Container.java:2083)
    at java.awt.Component.dispatchEventImpl(Component.java:4744)
    at java.awt.Container.dispatchEventImpl(Container.java:2141)
    at java.awt.Component.dispatchEvent(Component.java:4572)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4619)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4280)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4210)
    at java.awt.Container.dispatchEventImpl(Container.java:2127)
    at java.awt.Window.dispatchEventImpl(Window.java:2489)
    at java.awt.Component.dispatchEvent(Component.java:4572)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:710)
    at java.awt.EventQueue.access$400(EventQueue.java:82)
    at java.awt.EventQueue$2.run(EventQueue.java:669)
    at java.awt.EventQueue$2.run(EventQueue.java:667)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:98)
    at java.awt.EventQueue$3.run(EventQueue.java:683)
    at java.awt.EventQueue$3.run(EventQueue.java:681)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:680)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:296)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:211)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:201)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:196)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:188)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

I am really stuck on this, any help would be much appreciated, thanks so much in advance

Your title to the post looks odd. you dont get any nullpointer exception when you try to import any class. If a class is not found , then you'll get NoClassFound Exception. Maybe you are trying to accessing a object which has 'null' value. Try to figure out yourself , as this is a runtime excepiton, you dont know unless you go through your code carefully.

Edited 3 Years Ago by harinath_2007

Tracking down the cause of a NullPointerException is a simple matter of looking at the top of the stack trace which indicates the exact place where a null pointer was encountered. If the top method isn't one that you wrote, then go down the stack until you find a method that you wrote, but in this case you wrote the method at the top of the stack, and the line that the stack trace indicates is

        wordField.setText(game.showDashes());

There are only two ways that this line could cause a NullPointerException. Either wordField is null, or game is null. If this method weren't at the top of the stack and the exception had come from somewhere inside setText, then you would know that game.showDashes() had returned null, but as it is you just need to find out why wordField or game is null. You could modify the method so that it checks which one is null and narrows down your search, but in this case it is easy to check just by tracing the code by hand.

hai to all,

by look at your code the following these 2 things might be the one reason for the above problem i thought

at line no 44 and 45 of HangmanFrame class

you declared the 2 class variable references as a instance variavbles as follows

private HangmanGame game;
private WordGenerator myWord;

but those 2 references are declared but not instanciated at all thats the reason you got the NullPointerException

but inside the constructor you created those 2 objects but those references scopes are limited to inside the constructor only right.

i think you got my point

so replace these 2 line of inside the constructor

WordGenerator myWord = new WordGenerator();
HangmanGame game = new HangmanGame(myWord.getWord()); 

as follows

this.myWord = new WordGenerator();
this.game = new HangmanGame(myWord.getWord());

please try to do like that it may gives a solution i think

let me know the status after modifying the code

happy coding

Note: any comments are appreciated

Edited 3 Years Ago by radhakrishna.p: givingn the clarith on the solution

Yea, that was the problem. Didnt realise I had done something so silly. Works perfect now.

Thanks For the help everyone :)

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