• Post Reply Bookmark Topic Watch Topic
  • New Topic
programming forums Java Mobile Certification Databases Caching Books Engineering Micro Controllers OS Languages Paradigms IDEs Build Tools Frameworks Application Servers Open Source This Site Careers Other Pie Elite all forums
this forum made possible by our volunteer staff, including ...
Marshals:
  • Campbell Ritchie
  • Tim Cooke
  • paul wheaton
  • Jeanne Boyarsky
  • Ron McLeod
Sheriffs:
  • Paul Clapham
  • Liutauras Vilda
  • Devaka Cooray
Saloon Keepers:
  • Tim Holloway
  • Roland Mueller
Bartenders:

Why does this throw a NullPointerException?

 
Greenhorn
Posts: 10
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
So i set the TextField as Instance variable(It is not in a method block ich checked it multiple times.


It then gets a textfield which also appears in the GUI in this codeblock



I try to call fielda in this Line:



It compiles and runs ,but if i press the button firing the ActionEvent it prints the following:
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at PhythagoGUI.actionPerformed(PhythagoGUI.java:94)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:20
18)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.jav
a:2341)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel
.java:402)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259
)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonL
istener.java:252)
at java.awt.Component.processMouseEvent(Component.java:6505)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
at java.awt.Component.processEvent(Component.java:6270)
at java.awt.Container.processEvent(Container.java:2229)
at java.awt.Component.dispatchEventImpl(Component.java:4861)
at java.awt.Container.dispatchEventImpl(Container.java:2287)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832
)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)

at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
at java.awt.Container.dispatchEventImpl(Container.java:2273)
at java.awt.Window.dispatchEventImpl(Window.java:2719)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:723)
at java.awt.EventQueue.access$200(EventQueue.java:103)
at java.awt.EventQueue$3.run(EventQueue.java:682)
at java.awt.EventQueue$3.run(EventQueue.java:680)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDo
main.java:76)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDo
main.java:87)
at java.awt.EventQueue$4.run(EventQueue.java:696)
at java.awt.EventQueue$4.run(EventQueue.java:694)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDo
main.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:693)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThre
ad.java:242)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.
java:161)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThre
ad.java:150)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)

at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)

at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)




Line 94 is fielda.setText("Test")
I wnated the Text test to appear in the JTextField when pressing the Button.I hope someone can help me with this
 
Java Cowboy
Posts: 16084
88
Android Scala IntelliJ IDE Spring Java
  • Likes 1
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator

Colin Gebler wrote:So i set the TextField as Instance variable(It is not in a method block ich checked it multiple times.


It then gets a textfield which also appears in the GUI in this codeblock



Note that there are two variables named fielda. You have a member variable called fielda, and in the method guiErstellen you are creating a new, local variable also named fielda, which hides the member variable. You then initialize the local variable, and leave the member variable set to its default value null.

Most likely, you didn't mean to create a new, local variable named fielda in your method guiErstellen. So, don't do that; instead, initialize the member variable:

 
Colin Gebler
Greenhorn
Posts: 10
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
ah thank you very much ,it works now
 
I am going to test your electrical conductivity with this tiny ad:
Smokeless wood heat with a rocket mass heater
https://woodheat.net
reply
    Bookmark Topic Watch Topic
  • New Topic