Gui Exception

[Timmy21]

Hallo, bekomme folgende Fehlermeldung und habe keine Ahnung, wieso.
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at GuiTest.actionPerformed(GuiTest.java:27)
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:6414)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3275)
at java.awt.Component.processEvent(Component.java:6179)
at java.awt.Container.processEvent(Container.java:2084)
at java.awt.Component.dispatchEventImpl(Component.java:4776)
at java.awt.Container.dispatchEventImpl(Container.java:2142)
at java.awt.Component.dispatchEvent(Component.java:4604)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4618)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4279)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4209)
at java.awt.Container.dispatchEventImpl(Container.java:2128)
at java.awt.Window.dispatchEventImpl(Window.java:2492)
at java.awt.Component.dispatchEvent(Component.java:4604)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:717)
at java.awt.EventQueue.access$400(EventQueue.java:82)
at java.awt.EventQueue$2.run(EventQueue.java:676)
at java.awt.EventQueue$2.run(EventQueue.java:674)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:86)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:97)
at java.awt.EventQueue$3.run(EventQueue.java:690)
at java.awt.EventQueue$3.run(EventQueue.java:688)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:86)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:687)
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)


Habe 2 Klassen:

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

 class MeinPanel extends JPanel{

  public void paintComponent(Graphics g){
    int rot =  (int) (Math.random() *200);
    int grün = (int) (Math.random() *200);
    int blau = (int) (Math.random() *200);
    Color farbe = new Color(rot,grün,blau);
    g.setColor(farbe);
    g.fillRect(40,40,100,100);
  }
 }

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
  
public class GuiTest implements ActionListener{

  JFrame frame;
  JButton button1;
  JPanel panel;
  
  public void erstelleGui(){
    
    JFrame frame = new JFrame();
    JButton button1 = new JButton("klick mich um die farbe zu ändern");
    MeinPanel panel=new MeinPanel();
    
    frame.add(BorderLayout.SOUTH,button1);
    button1.addActionListener(this);
    frame.add(BorderLayout.CENTER,panel);
    frame.setVisible(true);
    frame.setSize(300,300);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
   
    
  }
  public void actionPerformed(ActionEvent event){
    frame.repaint();
  }
  
  public static void main(String[]args){
    GuiTest objekt=new GuiTest();
    objekt.erstelleGui();
    
  
  }
}

Danke im voraus

 

[Kevyzar]

Hallo Timmy21

Die Exception sagt dir sogar explizit wo der Fehler auftritt:

"Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at GuiTest.actionPerformed(GuiTest.java:27)" <- In GuiTest zeile 27


Du erstellt in "GuiErstellen" ein eigenes JFrame (Zeile 13)
Das Frame, dass du in "GuiErstellen Zeile 7 erstellst, hat somit noch überhaupt gar nichts zugewiesen, wenn ActionPerformed zum einsatz kommt, und wird es auch nicht haben.

Zeile 13 sollte demnach wie folgt lauten:

frame = new JFrame();
Ich hoffe das konnte dein Problem lösen, bin selbst noch nicht lange an Java dran

LG

 

[Timmy21]

Danke, supermagisch wie das jetzt doch funktioniert. Super. Sehr geiler Dorsch übrigens!