Im a very much a beginner programmer and i stumbled across this error code, when i try to click on my second, third and fourth MenuItem. The program runs, i can click the first MenuItem and the action is performed (leading me to a second class view). But when i try to click on the rest of the MenuItems or the 2 buttons with same action code (CLASS.show(); + dispose ();) i get this error:
- Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException: Cannot invoke "numerologi.views.Klientliste.show()" because "this.this$0.KLside" is null at numerologi.views.Program$3.actionPerformed(Program.java:120).......
So i understand that/where the error is at - on line 120 (and at the other MenuItem action lines) - but i dont know how to fix it? Please help!
I have now tried this and the error code stopped, but the action does not occurs? :
menuKliste.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
if (e == null) {
KLside.show();
dispose(); } }
});
My code:
package numerologi.views;
import java.awt.*;
import javax.swing.*;
import javax.swing.border.*;
import java.awt.event.*;
public class Program extends JFrame {
private JPanel contentPane, panel;
private JMenuBar menuBar;
private JMenu ForsideMenu;
private JMenuItem menuopret, menuKliste, menuNF, menuNliste;
private JLabel LabelVelkommen, ProgramMadeby;
private Opret ONside; //classes/sites
private Klientliste KLside;
private NF NFside;
private Navneliste NLside;
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
Program frame = new Program();
frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();}
}
});
}
public Program() {
initComponents();
createEvents(); }
private void initComponents() { //This method contains all codes for creating and initializing components.
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setBounds(100, 100, 1000, 600);
contentPane = new JPanel();
contentPane.setBackground(SystemColor.menu);
contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
setContentPane(contentPane);
contentPane.setLayout(null);
ProgramMadeby = new JLabel("Program made by Ellinoir");
ProgramMadeby.setFont(new Font("Tahoma", Font.PLAIN, 10));
ProgramMadeby.setBounds(10, 540, 192, 13);
contentPane.add(ProgramMadeby);
ONside = new Opret();
menuBar = new JMenuBar();
menuBar.setBounds(0, 0, 986, 22);
contentPane.add(menuBar);
ForsideMenu = new JMenu("Menu");
ForsideMenu.setHorizontalAlignment(SwingConstants.CENTER);
menuBar.add(ForsideMenu);
menuopret = new JMenuItem("Opret ny klient");
menuopret.setBackground(SystemColor.inactiveCaption);
ForsideMenu.add(menuopret);
menuKliste = new JMenuItem("Klientliste");
menuKliste.setBackground(SystemColor.inactiveCaption);
ForsideMenu.add(menuKliste);
ForsideMenu.addSeparator();
menuNF = new JMenuItem("Navne forandring");
menuNF.setBackground(SystemColor.inactiveCaption);
ForsideMenu.add(menuNF);
menuNliste = new JMenuItem("Navneliste");
menuNliste.setBackground(SystemColor.inactiveCaption);
ForsideMenu.add(menuNliste);
LabelVelkommen = new JLabel("Velkommen til numerologiens verden!");
LabelVelkommen.setFont(new Font("Tahoma", Font.BOLD, 27));
LabelVelkommen.setBackground(SystemColor.inactiveCaption);
LabelVelkommen.setBounds(230, 80, 543, 65);
contentPane.add(LabelVelkommen);
panel = new JPanel();
panel.setBackground(SystemColor.inactiveCaption);
panel.setBounds(130, 150, 750, 300);
contentPane.add(panel);
setIconImage(Toolkit.getDefaultToolkit().getImage(Program.class.getResource("/numerologi/resources/Diamond_512.png")));
setTitle("Numerologi program");
}
private void createEvents() { // This method contains all codes for creating events.
menuopret.addActionListener(new ActionListener() { //this one works
public void actionPerformed(ActionEvent e) {
ONside.show();
dispose(); }
});
menuKliste.addActionListener(new ActionListener() { //these don't
public void actionPerformed(ActionEvent e) {
KLside.show();
dispose(); }
});
menuNF.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
NFside.show();
dispose(); }
});
menuNliste.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
NLside.show();
dispose(); }
});
}
}
All error code:
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException: Cannot invoke "numerologi.views.Klientliste.show()" because "this.this$0.KLside" is null
at numerologi.views.Program$3.actionPerformed(Program.java:120)
at java.desktop/javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1967)
at java.desktop/javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2308)
at java.desktop/javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:405)
at java.desktop/javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:262)
at java.desktop/javax.swing.AbstractButton.doClick(AbstractButton.java:369)
at java.desktop/javax.swing.plaf.basic.BasicMenuItemUI.doClick(BasicMenuItemUI.java:1012)
at java.desktop/javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(BasicMenuItemUI.java:1056)
at java.desktop/java.awt.Component.processMouseEvent(Component.java:6614)
at java.desktop/javax.swing.JComponent.processMouseEvent(JComponent.java:3342)
at java.desktop/java.awt.Component.processEvent(Component.java:6379)
at java.desktop/java.awt.Container.processEvent(Container.java:2263)
at java.desktop/java.awt.Component.dispatchEventImpl(Component.java:4990)
at java.desktop/java.awt.Container.dispatchEventImpl(Container.java:2321)
at java.desktop/java.awt.Component.dispatchEvent(Component.java:4822)
at java.desktop/java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4919)
at java.desktop/java.awt.LightweightDispatcher.processMouseEvent(Container.java:4548)
at java.desktop/java.awt.LightweightDispatcher.dispatchEvent(Container.java:4489)
at java.desktop/java.awt.Container.dispatchEventImpl(Container.java:2307)
at java.desktop/java.awt.Window.dispatchEventImpl(Window.java:2769)
at java.desktop/java.awt.Component.dispatchEvent(Component.java:4822)
at java.desktop/java.awt.EventQueue.dispatchEventImpl(EventQueue.java:772)
at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:721)
at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:715)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:85)
at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:95)
at java.desktop/java.awt.EventQueue$5.run(EventQueue.java:745)
at java.desktop/java.awt.EventQueue$5.run(EventQueue.java:743)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:85)
at java.desktop/java.awt.EventQueue.dispatchEvent(EventQueue.java:742)
at java.desktop/java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:203)
at java.desktop/java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:124)
at java.desktop/java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:113)
at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:109)
at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
at java.desktop/java.awt.EventDispatchThread.run(EventDispatchThread.java:90)
