Menu class

[Kligham]

Hallo,

I have these two classes atm:

package test;

/*
 * Auteur
 */

import javax.swing.JFrame;

public class Main extends JFrame{

    public static void main(String[] args) {

    JFrame frame = new JFrame();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    [COLOR="red"][B]frame.setJMenuBar(new Menu());[/B][/COLOR]

    frame.pack();
    frame.setSize(500,500);
    frame.setVisible(true);

    }

}

and:

package test;

import javax.swing.*;
import java.awt.event.*;
[COLOR="red"][B]import java.awt.event.InputEvent.CTRL_DOWN_MASK;[/B][/COLOR]

public class Menu{

    public Menu (){

        JMenuBar menuBar = new JMenuBar();

        JMenu consultatie = new JMenu("Consultatie");
        menuBar.add(consultatie);
        JMenuItem nieuweClientItem= new JMenuItem("Nieuwe Cliënt");
        [B][COLOR="Red"]nieuweClientItem.setAccelerator(KeyStroke.getKeyStroke("C", CTRL_DOWN_MASK));[/COLOR][/B]
        consultatie.add(nieuweClientItem);

        JMenu boekhouding = new JMenu("Boekhouding");
        menuBar.add(boekhouding);

    }
}

Netbeans gives me 3 error signs, I underlined them in my code. What am I doing wrong?

[travishein]

the first error, need ot use JMenu I think, instead of Menu, when working with JFrame.

In general swing things have a "J*" version of their AWT counterparts.

e.g.

JFrame
JMenu
JMenItem
JButton

[pbrockway2]

Perhaps you could say what the error messages are if you don't understand them?

Generally they try to be self explanatory (but don't always succeed!).

A couple of things to watch out for: (1) You don't import a constant like InputEvent.CTRL_DOWN_MASK. Instead you import the class (whatever.InputEvent) and then use the static int value as InputEvent.CTRL_DOWN_MASK in your code.

(2) Have the API documentation open all the time! When you use a method the parameters must match what is required exactly. A char is not a String. The same goes for your own methods: a MenuBar is not a Menu.

[Kligham]

Hi,

I'll try to keep point 1 in mind. I changed it in my programe, and it doesn't give me an error anymore.

However, there is still one problem. I can't get my JMenubar displayed. I don't know if it is possible to add my menuBar from my Menu.java class to my JFrame wicht is in my Main.java class?

Main.java class:

package test;

/*
 * Auteur 
 */

import javax.swing.JFrame;

public class Main extends JFrame{

    public static void main(String[] args) {

    JFrame frame = new JFrame();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    [COLOR="Red"][B]frame.setJMenuBar(menuBar);[/B][/COLOR]

    frame.pack();
    frame.setSize(500,500);
    frame.setVisible(true);

    }

}

Menu.java:

package test;

import javax.swing.*;
import java.awt.event.*;
import java.awt.event.InputEvent.*;

public class Menu{

    public Menu (){

        JMenuBar menuBar = new JMenuBar();

        JMenu consultatie = new JMenu("Consultatie");
        menuBar.add(consultatie);
        JMenuItem nieuweClientItem= new JMenuItem("Nieuwe Cliënt");
        nieuweClientItem.setAccelerator(KeyStroke.getKeyStroke('C', InputEvent.CTRL_DOWN_MASK));
        consultatie.add(nieuweClientItem);

        JMenu boekhouding = new JMenu("Boekhouding");
        menuBar.add(boekhouding);

    }
}

The error that netbeans gives me is shown on the pic that I added.

+ Can anyone explain me what KeyEvent.VK_T does? I see it at alot of websites, but the never explain what it does.

[pbrockway2]

KeyEvent.VK_T is just an int. (for what it's worth, it's the value 84). It is used in a number of places where you want to refer to a key. For instance the KeyEvent class offers a getKeyCode() method. So you might have a method that gets invoked every time a key is pressed. This event would be sent an instance of KeyEvent at the time of the event and your method would call getKeyCode() to see what key was pressed. (eg if getKeyCode() returned KeyEvent.VK_T, ie 84, you would know that the "T" key had been pressed.

The best place for usage examples would be How to Write a Key Listener in Sun's Tutorial. The whole section on Swing is well worth reading.

In your example you seem to be using the Menu class to actually construct the menu bar that your frame will use. (The tutorial gives examples of constructing menu bars as well!) This is possible, but the Menu class should expose a "getter" method to return the menu bar which it constructs elsewhere (for instance in its constructor as you do now.)

Here's your code (but I changed the package name to what I think you mean) with a "getter" added:

package test;

import javax.swing.JFrame;

public class Main extends JFrame{
    public static void main(String[] args) {
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            // construct a Menu object...
        Menu menu = new Menu();
            // ...and obtain its menu bar
        frame.setJMenuBar(menu.getMenuBar());
	
        frame.pack();
        frame.setSize(500,500);
        frame.setVisible(true);
    }
}

package test;

import java.awt.event.InputEvent;

import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;
import javax.swing.KeyStroke;

public class Menu {

    private JMenuBar menuBar;

        /** Constructs the menu bar. */
    public Menu() {
        menuBar = new JMenuBar();

        JMenu consultatie = new JMenu("Consultatie");
        menuBar.add(consultatie);
        JMenuItem nieuweClientItem= new JMenuItem("Nieuwe Cliënt");
        nieuweClientItem.setAccelerator(KeyStroke.getKeyStroke(
                'C', InputEvent.CTRL_DOWN_MASK));
        consultatie.add(nieuweClientItem);

        JMenu boekhouding = new JMenu("Boekhouding");
        menuBar.add(boekhouding);
    }

        /** Returns the menu bar corresponding to this menu. */
    public JMenuBar getMenuBar() {return menuBar;}
}

[Kligham]

Hi,

Thanks for the help mate. I've got a better insight on constructors as well. I works as it should be.

[camickr]

Would just like to add that the AWT package already has a class called "Menu". So you should rename yours to avoid confusion.

[Kligham]

Thx, i'll rename it.

[r035198x]

Would just like to add that the AWT package already has a class called "Menu". So you should rename yours to avoid confusion.

While we are at it ....
Your Main class extends JFrame for no apparent reason. Your Main class isn't a JFrame at all it is?

[Kligham]

Thx to let me know. I removed it, and it still works. I added that because I thought you needed to do that if you are creating a JFame, but apparently not.

[Tolls]

You also ought to look at the tutorials for Swing (possibly even run through the straight Java ones as well). Especially this bit for the Swing stuff, since you may as well write this stuff properly from the getgo.

[Kligham]

What do you mean with getgo? + I don't fully understand the articles about the threads. Can you maybe point out about what is wrong with the program I wrote (in function of those treads) and what I should look out for?

[Tolls]

From the getgo...from the start.
I knew I shouldn't have typed that as I was posting it. Oh well.

The last link (about threads) shows how you ought to launch a Swing app:

SwingUtilities.invokeLater(new Runnable() {
    public void run() {
        createAndShowGUI();
    }
});

This would be in your main() method and the createAndShowGUI() method would be a static method containing all the code you currently have in main(). It's all about how the thread that the Swing GUI works under (the event dispatcher thread), works.

[Kligham]

From the getgo...from the start.
I knew I shouldn't have typed that as I was posting it. Oh well.

The last link (about threads) shows how you ought to launch a Swing app:

SwingUtilities.invokeLater(new Runnable() {
    public void run() {
        createAndShowGUI();
    }
});

This would be in your main() method and the createAndShowGUI() method would be a static method containing all the code you currently have in main(). It's all about how the thread that the Swing GUI works under (the event dispatcher thread), works.

So you mean that I need to type it this way then?

package test;

import javax.swing.JFrame;

public class Main extends JFrame{

    public void createAndShowGUI(){

        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            // construct a Menu object...
        Menu menu = new Menu();
            // ...and obtain its menu bar
        frame.setJMenuBar(menu.getMenuBar());
	
        frame.pack();
        frame.setSize(500,500);
        frame.setVisible(true);


    }

    public static void main(String[] args) {
            
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();
    }
});

}
}

And do I only have to do this in my main class or everywhere I would have a part of GUI-stuff that needs to be created if some event has been triggered?

[Tolls]

Yep. That's what you'll find on all the Swing tutorials, as far as I can remember.
It's purely a Swing thing so that all GUI stuff is run on the Event thread. The event thread is also where all events occur, so you don't have to worry about that after this.

There is a similar thing, though, when you are doing some heavy non-GUI processing as the result of an event (say a database search) where you would create a worker thread, but that's probably more than you need to know at the moment. (It's a bit further on on that Swing threading tutorial).