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Sep 22nd, 2009
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Menu Not Displaying

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I'm using documentation on sun.com to try and learn Java. I was trying a simple Notepad type program but cannot get the menus to display. I'm receiving no errors and cannot figure out what I've done wrong and/or left out.

Java Syntax (Toggle Plain Text)
  1. import javax.swing.*;
  2. import java.awt.*;
  3. import java.awt.event.*;
  4.  
  5.  
  6.  
  7. public class NotepadInJava //implements ActionListener
  8. {
  9.     //preparing container
  10.     JFrame notepadFrame;
  11.     JTextArea theTextArea;
  12.     JScrollPane scrollPane = new JScrollPane(theTextArea);
  13.  
  14.  
  15.     //File menu items
  16.     JMenu file;
  17.     JMenuItem open;
  18.     JMenuItem save;
  19.     JMenuItem exit;
  20.  
  21.     //Edit menu items
  22.     JMenu edit;
  23.     JMenuItem copy;
  24.     JMenuItem cut;
  25.     JMenuItem selectAll;
  26.     JMenuItem paste;
  27.  
  28.     public static void main(String[] args)
  29.     {
  30.         NotepadInJava app = new NotepadInJava();
  31.     }
  32.  
  33.     public NotepadInJava()
  34.     {
  35.         notepadFrame = new JFrame();
  36.         notepadFrame.addWindowListener(null);
  37.         notepadFrame.setSize(600,600);
  38.         notepadFrame.setLocation(40,20);
  39.         notepadFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  40.         notepadFrame.setVisible(true);
  41.         buildMenus();
  42.     }
  43.  
  44.     private void buildMenus()
  45.     {
  46.       //create menu bar
  47.         JMenuBar MenuBar = new JMenuBar();
  48.       //notepadFrame.setJMenuBar(FileMenuBar);
  49.  
  50.       //build File menu
  51.         file = new JMenu("File");
  52.         MenuBar.add(file);
  53.       //add Open to File menu
  54.         open = new JMenuItem("Open");
  55.         open.addActionListener(null);
  56.         MenuBar.add(open);
  57.       //add Save to File category
  58.         save = new JMenuItem("Save");
  59.         save.addActionListener(null);
  60.         MenuBar.add(save);
  61.       //add Exit to File category
  62.         exit = new JMenuItem("Exit");
  63.         exit.addActionListener(null);
  64.         MenuBar.add(exit);
  65.  
  66.       //build Edit menu
  67.         edit = new JMenu("Edit");
  68.         MenuBar.add(edit);
  69.       //add Copy to Edit category
  70.         copy = new JMenuItem("Copy");
  71.         copy.addActionListener(null);
  72.         MenuBar.add(copy);
  73.       //add Cut to Edit category
  74.         cut = new JMenuItem("Cut");
  75.         cut.addActionListener(null);
  76.         MenuBar.add(cut);
  77.       //add Select All to Edit category
  78.         selectAll = new JMenuItem("Select All");
  79.         selectAll.addActionListener(null);
  80.         MenuBar.add(selectAll);
  81.       //add Paste to Edit category
  82.         paste = new JMenuItem("Paste");
  83.         paste.addActionListener(null);
  84.         MenuBar.add(paste);
  85.     }
  86. }
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Reputation Points: 10
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Junior Poster
kahaj is offline Offline
193 posts
since Sep 2005
Permalink
Sep 22nd, 2009
0

Re: Menu Not Displaying

You did not added menu bar to your frame setJMenuBar(JMenuBar menubar)
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peter_budo is offline Offline
6,656 posts
since Dec 2004
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Sep 22nd, 2009
1

Re: Menu Not Displaying

Peter_budo you beat me to it! Kahaj, what you could do is :

declare and initialize MenuBar as a class field, instead of a local variable in method buildMenus() :

java Syntax (Toggle Plain Text)
  1. JMenuBar MenuBar;

you can then initialize this variable in the class constructor:

java Syntax (Toggle Plain Text)
  1. MenuBar = new JMenuBar()

then add MenuBar to notepadFrame before you call method buildMenus():

java Syntax (Toggle Plain Text)
  1. notepadFrame.add(MenuBar);

Hope that helps.
P.S. you might want to look at layout managers for the menu items, I recomend the tutorials here:
http://java.sun.com/docs/books/tutor...out/using.html
Last edited by majestic0110; Sep 22nd, 2009 at 3:35 pm. Reason: typos, tidy up
Reputation Points: 256
Solved Threads: 72
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majestic0110 is offline Offline
1,306 posts
since Oct 2007
Permalink
Sep 22nd, 2009
0

Re: Menu Not Displaying

I'm sure once I've dealt with menus more, they'll be easier. But right now, they're really a pain in the butt.

Here are the changes I made:
Java Syntax (Toggle Plain Text)
  1. import javax.swing.*;
  2. import java.awt.*;
  3. import java.awt.event.*;
  4.  
  5.  
  6.  
  7. public class NotepadInJava //implements ActionListener
  8. {
  9.     //preparing container
  10.     JFrame notepadFrame;
  11.     JMenuBar MenuBar;
  12.     JTextArea theTextArea;
  13.     JScrollPane scrollPane = new JScrollPane(theTextArea);
  14.  
  15.  
  16.     //File menu items
  17.     JMenu file;
  18.     JMenuItem open;
  19.     JMenuItem save;
  20.     JMenuItem exit;
  21.  
  22.     //Edit menu items
  23.     JMenu edit;
  24.     JMenuItem copy;
  25.     JMenuItem cut;
  26.     JMenuItem selectAll;
  27.     JMenuItem paste;
  28.  
  29.     public static void main(String[] args)
  30.     {
  31.         NotepadInJava app = new NotepadInJava();
  32.     }
  33.  
  34.     public NotepadInJava()
  35.     {
  36.         notepadFrame = new JFrame();
  37.         notepadFrame.addWindowListener(null);
  38.         notepadFrame.setSize(600,600);
  39.         notepadFrame.setLocation(40,20);
  40.         notepadFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  41.         notepadFrame.setVisible(true);
  42.         buildMenus();
  43.     }
  44.  
  45.     private void buildMenus()
  46.     {
  47.       //create menu bar
  48.         JMenuBar MenuBar = new JMenuBar();
  49.         notepadFrame.setJMenuBar(MenuBar);
  50.  
  51.       //build File menu
  52.         file = new JMenu("File");
  53.         MenuBar.add(file);
  54.       //add Open to File menu
  55.         open = new JMenuItem("Open");
  56.         open.addActionListener(null);
  57.         MenuBar.add(open);
  58.       //add Save to File category
  59.         save = new JMenuItem("Save");
  60.         save.addActionListener(null);
  61.         MenuBar.add(save);
  62.       //add Exit to File category
  63.         exit = new JMenuItem("Exit");
  64.         exit.addActionListener(null);
  65.         MenuBar.add(exit);
  66.  
  67.       //build Edit menu
  68.         edit = new JMenu("Edit");
  69.         MenuBar.add(edit);
  70.       //add Copy to Edit category
  71.         copy = new JMenuItem("Copy");
  72.         copy.addActionListener(null);
  73.         MenuBar.add(copy);
  74.       //add Cut to Edit category
  75.         cut = new JMenuItem("Cut");
  76.         cut.addActionListener(null);
  77.         MenuBar.add(cut);
  78.       //add Select All to Edit category
  79.         selectAll = new JMenuItem("Select All");
  80.         selectAll.addActionListener(null);
  81.         MenuBar.add(selectAll);
  82.       //add Paste to Edit category
  83.         paste = new JMenuItem("Paste");
  84.         paste.addActionListener(null);
  85.         MenuBar.add(paste);
  86.     }
  87. }
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Junior Poster
kahaj is offline Offline
193 posts
since Sep 2005
Permalink
Sep 22nd, 2009
0

Re: Menu Not Displaying

You need to add:

java Syntax (Toggle Plain Text)
  1. notepadFrame.add(MenuBar);

before you set notepadFrame.setVisible(true);. This adds the MenuBar to the Frame.
Reputation Points: 256
Solved Threads: 72
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majestic0110 is offline Offline
1,306 posts
since Oct 2007
Permalink
Sep 22nd, 2009
0

Re: Menu Not Displaying

Here's the code I have so far:
Java Syntax (Toggle Plain Text)
  1. import javax.swing.*;
  2. import java.awt.*;
  3. import java.awt.event.*;
  4.  
  5.  
  6.  
  7. public class NotepadInJava //implements ActionListener
  8. {
  9.     //preparing container
  10.     JFrame notepadFrame;
  11.     JMenuBar MenuBar;
  12.     JTextArea theTextArea;
  13.     JScrollPane scrollPane = new JScrollPane(theTextArea);
  14.  
  15.  
  16.     //File menu items
  17.     JMenu file;
  18.     JMenuItem open;
  19.     JMenuItem save;
  20.     JMenuItem exit;
  21.  
  22.     //Edit menu items
  23.     JMenu edit;
  24.     JMenuItem copy;
  25.     JMenuItem cut;
  26.     JMenuItem selectAll;
  27.     JMenuItem paste;
  28.  
  29.     public static void main(String[] args)
  30.     {
  31.         NotepadInJava app = new NotepadInJava();
  32.     }
  33.  
  34.     public NotepadInJava()
  35.     {
  36.         buildMenus();
  37.         notepadFrame = new JFrame();
  38.         notepadFrame.add(MenuBar);
  39.         notepadFrame.addWindowListener(null);
  40.         notepadFrame.setSize(600,600);
  41.         notepadFrame.setLocation(40,20);
  42.         notepadFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  43.         notepadFrame.setVisible(true);      
  44.     }
  45.  
  46.     private void buildMenus()
  47.     {
  48.       //create menu bar
  49.         JMenuBar MenuBar = new JMenuBar();
  50.         notepadFrame.setJMenuBar(MenuBar);
  51.  
  52.       //build File menu
  53.         file = new JMenu("File");
  54.         MenuBar.add(file);
  55.       //add Open to File menu
  56.         open = new JMenuItem("Open");
  57.         open.addActionListener(null);
  58.         MenuBar.add(open);
  59.       //add Save to File category
  60.         save = new JMenuItem("Save");
  61.         save.addActionListener(null);
  62.         MenuBar.add(save);
  63.       //add Exit to File category
  64.         exit = new JMenuItem("Exit");
  65.         exit.addActionListener(null);
  66.         MenuBar.add(exit);
  67.  
  68.       //build Edit menu
  69.         edit = new JMenu("Edit");
  70.         MenuBar.add(edit);
  71.       //add Copy to Edit category
  72.         copy = new JMenuItem("Copy");
  73.         copy.addActionListener(null);
  74.         MenuBar.add(copy);
  75.       //add Cut to Edit category
  76.         cut = new JMenuItem("Cut");
  77.         cut.addActionListener(null);
  78.         MenuBar.add(cut);
  79.       //add Select All to Edit category
  80.         selectAll = new JMenuItem("Select All");
  81.         selectAll.addActionListener(null);
  82.         MenuBar.add(selectAll);
  83.       //add Paste to Edit category
  84.         paste = new JMenuItem("Paste");
  85.         paste.addActionListener(null);
  86.         MenuBar.add(paste);
  87.     }
  88. }

...and here's what the Debugger is yelling at me. To be totally honest, I'm not grasping what it is not liking about it.
Java Syntax (Toggle Plain Text)
  1. run:
  2. Exception in thread "main" java.lang.NullPointerException
  3.         at NotepadInJava.buildMenus(NotepadInJava.java:50)
  4.         at NotepadInJava.<init>(NotepadInJava.java:36)
  5.         at NotepadInJava.main(NotepadInJava.java:31)
  6. Java Result: 1
  7. BUILD SUCCESSFUL (total time: 2 seconds)
Reputation Points: 10
Solved Threads: 0
Junior Poster
kahaj is offline Offline
193 posts
since Sep 2005
Permalink
Sep 22nd, 2009
1

Re: Menu Not Displaying

Ok the problem there is that you have not initialized the variable MenuBar before you call the method buildMenus() on it, therefore you get a null pointer exception. You need to initialize MenuBar before you can perform any action on it. Change your constructor from this :

java Syntax (Toggle Plain Text)
  1. public NotepadInJava()
  2.     {
  3.         buildMenus();
  4.         notepadFrame = new JFrame();
  5.         notepadFrame.add(MenuBar);
  6.         notepadFrame.addWindowListener(null);
  7.         notepadFrame.setSize(600,600);
  8.         notepadFrame.setLocation(40,20);
  9.         notepadFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  10.         notepadFrame.setVisible(true);      
  11.     }

to this :

java Syntax (Toggle Plain Text)
  1. public NotepadInJava()
  2.     {
  3.         MenuBar = new JMenuBar();
  4.         notepadFrame = new JFrame();
  5.         notepadFrame.add(MenuBar);
  6.         buildMenus();
  7.         notepadFrame.addWindowListener(null);
  8.         notepadFrame.setSize(600,600);
  9.         notepadFrame.setLocation(40,20);
  10.         notepadFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  11.         notepadFrame.setVisible(true);
  12.     }

This will solve your null pointer exception. Look here for more information regarding null pointer exceptions :

http://java.sun.com/j2se/1.5.0/docs/...Exception.html


EDIT: Oh and remove this line :

java Syntax (Toggle Plain Text)
  1. JMenuBar MenuBar = new JMenuBar();

from method buildMenus() as you don't want to initialize MenuBar twice!
Last edited by majestic0110; Sep 22nd, 2009 at 6:02 pm. Reason: see edit note
Reputation Points: 256
Solved Threads: 72
Nearly a Posting Virtuoso
majestic0110 is offline Offline
1,306 posts
since Oct 2007

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