# Guibuilder -\> Event -\> NullPointerException

**URL:** <https://discourse.processing.org/t/guibuilder-event-nullpointerexception/32104>\
**Category:** Libraries\
**Created:** [September 5, 2021, 3:43pm UTC](https://discourse.processing.org/t/guibuilder-event-nullpointerexception/32104 "2021-09-05T15:43:11Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![Student001](https://avatars.discourse-cdn.com/v4/letter/s/77aa72/32.png) [@Student001](https://discourse.processing.org/u/Student001)\
**Post date:** [September 5, 2021, 3:43pm UTC](https://discourse.processing.org/t/guibuilder-event-nullpointerexception/32104/1 "2021-09-05T15:43:11Z")

</div>

Hi!

this code produces a NullPointerException:

```auto
public void tf_step_delay_change(GTextField source, GEvent event) { //_CODE_:tf_step_delay:234478:
  if(event == GEvent.ENTERED){
     slider_step_delay.setValue(Integer.valueOf(source.getText()));
  }
} //_CODE_:tf_step_delay:234478:

```

```auto
java.lang.NullPointerException
	at g4p_controls.GTextField.keyEvent(Unknown Source)
	at g4p_controls.GWindowImpl.sendKeyEvent(Unknown Source)
	at g4p_controls.GWindowImpl.keyEvent(Unknown Source)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:566)
	at processing.core.PApplet$RegisteredMethods.handle(PApplet.java:1395)
	at processing.core.PApplet.handleMethods(PApplet.java:1549)
	at processing.core.PApplet.handleKeyEvent(PApplet.java:2797)
	at processing.core.PApplet.dequeueEvents(PApplet.java:2385)
	at processing.core.PApplet.handleDraw(PApplet.java:2220)
	at processing.awt.PSurfaceAWT$10.callDraw(PSurfaceAWT.java:1419)
	at processing.core.PSurfaceNone$AnimationThread.run(PSurfaceNone.java:354)
NullPointerException

```

Why?

---

<div class="post-metadata">

**Author:** ![quark](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/quark/32/26_2.png) [@quark](https://discourse.processing.org/u/quark)\
**Post date:** [September 5, 2021, 4:05pm UTC](https://discourse.processing.org/t/guibuilder-event-nullpointerexception/32104/2 "2021-09-05T16:05:33Z")

</div>

I can’t see how that exception can be created from that event handler.

If the slider `slider_step_delay` has been created before this method has been executed then there is no code inside the event handler that could generate a NPE.

I assume that you are not calling the `keyEvent` method directly from your own code. That is not permitted.

If an exception had been thrown in this event handler you would get a stack trace like

```auto
################ EXCEPTION IN EVENT HANDLER ################
An error occured during execution of the eventhandler:
CLASS: sketch_210905a METHOD: tf_step_delay_change
	Caused by java.lang.NumberFormatException: null
	java.lang.Integer.parseInt(Integer.java:542)
	java.lang.Integer.valueOf(Integer.java:766)
	sketch_210905a.tf_step_delay_change(sketch_210905a.java:63)
	sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	java.lang.reflect.Method.invoke(Method.java:498)
	g4p_controls.GAbstractControl.fireEvent(Unknown Source)
	g4p_controls.GTextField.keyTypedProcess(Unknown Source)
	g4p_controls.GTextField.keyEvent(Unknown Source)
	g4p_controls.GWindowImpl.sendKeyEvent(Unknown Source)
	g4p_controls.GWindowImpl.keyEvent(Unknown Source)
	sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	java.lang.reflect.Method.invoke(Method.java:498)
	processing.core.PApplet$RegisteredMethods.handle(PApplet.java:1436)
	processing.core.PApplet.handleMethods(PApplet.java:1638)
	processing.core.PApplet.handleKeyEvent(PApplet.java:3021)
	processing.core.PApplet.dequeueEvents(PApplet.java:2655)
	processing.core.PApplet.handleDraw(PApplet.java:2493)
	processing.awt.PSurfaceAWT$12.callDraw(PSurfaceAWT.java:1547)
	processing.core.PSurfaceNone$AnimationThread.run(PSurfaceNone.java:313)
##############################################################

```