Im stuck today with a java error on an eclipse 3.8 platform.
I try to generate a simple MenuBar on a JFrame. The JMenuBar contains the JMenu("Help") and the JMenu contains a JMenuItem("Quit"). The class extends a JFrame. With the function (this.)setJMenuBar(MenuBar); I try to set my MenuBar to my JFrame, which should work fine as long I just have one MenuBar.
GUI-class code:
import javax.swing.*;
import java.awt.*;
public class Taschenrechner extends JFrame{
//Instanzvariablen im Zusamenhang mit dem Menu
private JMenuBar MenuBar;
private JMenu MenuHelp;
private JMenuItem MenuHelpQuit;
public Taschenrechner() {
super();
//Flaeche festlegen
this.setSize(300,300);
//Menukomponenten definieren
MenuHelp= new JMenu("Help");
MenuHelpQuit=new JMenuItem("Quit");
//Menukomponenten zusammensetzen
MenuHelp.add(MenuHelpQuit);
MenuBar.add(MenuHelp);
this.setJMenuBar(MenuBar);
}
}
my main-class code (declare objekt and setVisible):
public class Taschenrechnerstart {
public static void main(String[] args) {
Taschenrechner taschenrechner1 = new Taschenrechner();
taschenrechner1.setVisible(true);
}
}
Now on starting the code I get a NullPointerException-error in the GUI-class on line:
MenuBar.add(MenuHelp);
and a NullPointerException-error in the main-class on the line:
Taschenrechner taschenrechner1 = new Taschenrechner();
Does someone have an idea why my code isn't working?
MenuBar.add(MenuHelp);
You are accessing the MenuBar variable without initializing it.
You are missing a
MenuBar = new JMenuBar (..);
BTW, your code would be more readable if you use Java naming conventions (variables should start with a lower case letter).
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