Thursday, December 23, 2021

[FIXED] JavaFX choice box null pointer exception while switching scene

December 23, 2021 javafx, nullpointerexception

Issue

The program basically display choice box and a button and whatever the user choose it will print it in a label in scene 2. But this error just keep coming.

There are to errors occurs one when I select an item from choice box menu and the other when I press the button.

Note: I'm using same Controller class for both fxml files.

The error:


javafx.fxml.LoadException: 
/C:/Users/yasse/eclipse-workspace/FinalProject/bin/application/exscene2.fxml

   at javafx.fxml/javafx.fxml.FXMLLoader.constructLoadException(FXMLLoader.java:2707)
   at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2685)
   at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2548)
   at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3331)
   at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3287)
   at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3255)
   at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3227)
   at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3203)
   at javafx.fxml/javafx.fxml.FXMLLoader.load(FXMLLoader.java:3196)
   at application.BookController.switchscene(BookController.java:57)
   at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
   at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:234)
   at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
   at javafx.base/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
   at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
   at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
   at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
   at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
   at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
   at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
   at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
   at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
   at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
   at javafx.graphics/javafx.scene.Node.fireEvent(Node.java:8792)
   at javafx.controls/javafx.scene.control.ChoiceBox$4.invalidated(ChoiceBox.java:333)
   at javafx.base/javafx.beans.property.ObjectPropertyBase.markInvalid(ObjectPropertyBase.java:112)
   at javafx.base/javafx.beans.property.ObjectPropertyBase.set(ObjectPropertyBase.java:147)
   at javafx.controls/javafx.scene.control.ChoiceBox.setValue(ChoiceBox.java:342)
   at javafx.controls/javafx.scene.control.ChoiceBox.lambda$new$1(ChoiceBox.java:194)
   at javafx.base/com.sun.javafx.binding.ExpressionHelper$SingleChange.fireValueChangedEvent(ExpressionHelper.java:181)
   at javafx.base/com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(ExpressionHelper.java:80)
   at javafx.base/javafx.beans.property.ReadOnlyObjectPropertyBase.fireValueChangedEvent(ReadOnlyObjectPropertyBase.java:80)
   at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:449)
   at javafx.graphics/com.sun.glass.ui.View.handleMouseEvent(View.java:557)
   at javafx.graphics/com.sun.glass.ui.View.notifyMouse(View.java:943)
   at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
   at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:184)
   at java.base/java.lang.Thread.run(Thread.java:831)
Caused by: java.lang.NullPointerException: Cannot invoke "javafx.scene.control.ChoiceBox.getItems()" because "this.box" is null
   at application.BookController.initialize(BookController.java:44)
   at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2655)
   ... 79 more
Exception in thread "JavaFX Application Thread" java.lang.NullPointerException: Cannot invoke "javafx.scene.control.Label.setText(String)" because "this.label" is null
   at application.BookController.switchscene(BookController.java:66)
   at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
   at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:234)
   at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
   at javafx.base/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
   at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
   at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
   at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
   at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
   at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
   at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
   at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
   at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
   at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
   at javafx.graphics/javafx.scene.Node.fireEvent(Node.java:8792)
   at javafx.controls/javafx.scene.control.ChoiceBox$4.invalidated(ChoiceBox.java:333)
   at javafx.base/javafx.beans.property.ObjectPropertyBase.markInvalid(ObjectPropertyBase.java:112)
   at javafx.base/javafx.beans.property.ObjectPropertyBase.set(ObjectPropertyBase.java:147)
   at javafx.controls/javafx.scene.control.ChoiceBox.setValue(ChoiceBox.java:342)
   at javafx.controls/javafx.scene.control.ChoiceBox.lambda$new$1(ChoiceBox.java:194)
   at javafx.base/com.sun.javafx.binding.ExpressionHelper$SingleChange.fireValueChangedEvent(ExpressionHelper.java:181)
   at javafx.base/com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(ExpressionHelper.java:80)
   at javafx.base/javafx.beans.property.ReadOnlyObjectPropertyBase.fireValueChangedEvent(ReadOnlyObjectPropertyBase.java:80)
   at javafx.base/javafx.beans.property.ReadOnlyObjectWrapper.fireValueChangedEvent(ReadOnlyObjectWrapper.java:102)
   at javafx.base/javafx.beans.property.ObjectPropertyBase.markInvalid(ObjectPropertyBase.java:113)
   at javafx.base/javafx.beans.property.ObjectPropertyBase.set(ObjectPropertyBase.java:147)
   at javafx.controls/javafx.scene.control.SelectionModel.setSelectedItem(SelectionModel.java:105)
   at javafx.controls/javafx.scene.control.SingleSelectionModel.updateSelectedIndex(SingleSelectionModel.java:223)
   at javafx.controls/javafx.scene.control.SingleSelectionModel.select(SingleSelectionModel.java:149)
   at javafx.controls/javafx.scene.control.ChoiceBox$ChoiceBoxSelectionModel.select(ChoiceBox.java:586)
   at javafx.controls/javafx.scene.control.skin.ChoiceBoxSkin.lambda$addPopupItem$7(ChoiceBoxSkin.java:390)
   at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
   at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:234)
   at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
   at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
   at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
   at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
   at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
   at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
   at javafx.controls/javafx.scene.control.MenuItem.fire(MenuItem.java:459)
   at javafx.controls/com.sun.javafx.scene.control.ContextMenuContent$MenuItemContainer.doSelect(ContextMenuContent.java:1385)
   at javafx.controls/com.sun.javafx.scene.control.ContextMenuContent$MenuItemContainer.lambda$createChildren$12(ContextMenuContent.java:1338)
   at javafx.base/com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:247)
   at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
   at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:234)
   at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
   at javafx.base/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
   at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
   at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
   at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
   at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
   at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
   at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
   at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
   at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
   at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
   at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
   at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
   at javafx.graphics/javafx.scene.Scene$MouseHandler.process(Scene.java:3897)
   at javafx.graphics/javafx.scene.Scene.processMouseEvent(Scene.java:1878)
   at javafx.graphics/javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2623)
   at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:411)
   at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:301)
   at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
   at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$2(GlassViewEventHandler.java:450)
   at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:424)
   at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:449)
   at javafx.graphics/com.sun.glass.ui.View.handleMouseEvent(View.java:557)
   at javafx.graphics/com.sun.glass.ui.View.notifyMouse(View.java:943)
   at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
   at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:184)
   at java.base/java.lang.Thread.run(Thread.java:831)
javafx.fxml.LoadException: 
/C:/Users/yasse/eclipse-workspace/FinalProject/bin/application/exscene2.fxml

   at javafx.fxml/javafx.fxml.FXMLLoader.constructLoadException(FXMLLoader.java:2707)
   at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2685)
   at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2548)
   at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3331)
   at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3287)
   at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3255)
   at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3227)
   at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3203)
   at javafx.fxml/javafx.fxml.FXMLLoader.load(FXMLLoader.java:3196)
   at application.BookController.switchscene(BookController.java:57)
   at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
   at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:78)
   at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
   at java.base/java.lang.reflect.Method.invoke(Method.java:567)
   at com.sun.javafx.reflect.Trampoline.invoke(MethodUtil.java:77)
   at jdk.internal.reflect.GeneratedMethodAccessor2.invoke(Unknown Source)
   at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
   at java.base/java.lang.reflect.Method.invoke(Method.java:567)
   at javafx.base/com.sun.javafx.reflect.MethodUtil.invoke(MethodUtil.java:275)
   at javafx.fxml/com.sun.javafx.fxml.MethodHelper.invoke(MethodHelper.java:84)
   at javafx.fxml/javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1852)
   at javafx.fxml/javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1724)
   at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
   at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:234)
   at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
   at javafx.base/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
   at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
   at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
   at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
   at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
   at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
   at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
   at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
   at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
   at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
   at javafx.graphics/javafx.scene.Node.fireEvent(Node.java:8792)
   at javafx.controls/javafx.scene.control.Button.fire(Button.java:203)
   at javafx.controls/com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:208)
   at javafx.controls/com.sun.javafx.scene.control.inputmap.InputMap.handle(InputMap.java:274)
   at javafx.base/com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:247)
   at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
   at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:234)
   at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
   at javafx.base/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
   at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
   at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
   at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
   at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
   at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
   at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
   at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
   at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
   at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
   at javafx.graphics/javafx.scene.Scene$MouseHandler.process(Scene.java:3897)
   at javafx.graphics/javafx.scene.Scene.processMouseEvent(Scene.java:1878)
   at javafx.graphics/javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2623)
   at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:411)
   at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:301)
   at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
   at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$2(GlassViewEventHandler.java:450)
   at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:424)
   at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:449)
   at javafx.graphics/com.sun.glass.ui.View.handleMouseEvent(View.java:557)
   at javafx.graphics/com.sun.glass.ui.View.notifyMouse(View.java:943)
   at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
   at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:184)
   at java.base/java.lang.Thread.run(Thread.java:831)
Caused by: java.lang.NullPointerException: Cannot invoke "javafx.scene.control.ChoiceBox.getItems()" because "this.box" is null
   at application.BookController.initialize(BookController.java:44)
   at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2655)
   ... 65 more
Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
   at javafx.fxml/javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1857)
   at javafx.fxml/javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1724)
   at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
   at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:234)
   at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
   at javafx.base/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
   at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
   at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
   at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
   at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
   at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
   at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
   at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
   at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
   at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
   at javafx.graphics/javafx.scene.Node.fireEvent(Node.java:8792)
   at javafx.controls/javafx.scene.control.Button.fire(Button.java:203)
   at javafx.controls/com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:208)
   at javafx.controls/com.sun.javafx.scene.control.inputmap.InputMap.handle(InputMap.java:274)
   at javafx.base/com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:247)
   at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
   at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:234)
   at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
   at javafx.base/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
   at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
   at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
   at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
   at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
   at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
   at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
   at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
   at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
   at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
   at javafx.graphics/javafx.scene.Scene$MouseHandler.process(Scene.java:3897)
   at javafx.graphics/javafx.scene.Scene.processMouseEvent(Scene.java:1878)
   at javafx.graphics/javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2623)
   at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:411)
   at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:301)
   at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
   at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$2(GlassViewEventHandler.java:450)
   at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:424)
   at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:449)
   at javafx.graphics/com.sun.glass.ui.View.handleMouseEvent(View.java:557)
   at javafx.graphics/com.sun.glass.ui.View.notifyMouse(View.java:943)
   at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
   at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:184)
   at java.base/java.lang.Thread.run(Thread.java:831)
Caused by: java.lang.reflect.InvocationTargetException
   at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
   at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:78)
   at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
   at java.base/java.lang.reflect.Method.invoke(Method.java:567)
   at com.sun.javafx.reflect.Trampoline.invoke(MethodUtil.java:77)
   at jdk.internal.reflect.GeneratedMethodAccessor2.invoke(Unknown Source)
   at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
   at java.base/java.lang.reflect.Method.invoke(Method.java:567)
   at javafx.base/com.sun.javafx.reflect.MethodUtil.invoke(MethodUtil.java:275)
   at javafx.fxml/com.sun.javafx.fxml.MethodHelper.invoke(MethodHelper.java:84)
   at javafx.fxml/javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1852)
   ... 46 more
Caused by: java.lang.NullPointerException: Cannot invoke "javafx.scene.control.Label.setText(String)" because "this.label" is null
   at application.BookController.switchscene(BookController.java:66)
   ... 57 more

My Main:

package application;    
import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.stage.Stage;
import javafx.scene.Scene;
import javafx.scene.layout.AnchorPane;



public class Main extends Application {
    //@Override
    public void start( Stage primaryStage) throws Exception {
        // TODO Auto-generated method stub
        
        AnchorPane mainpane= (AnchorPane) FXMLLoader.load(Main.class.getResource("exscene1.fxml"));
        primaryStage.setScene(new Scene(mainpane));
        
        primaryStage.show();
        
        
        
    }
    
    public static void main(String[] args) {
        Application.launch(args);
    }
}

My Controller class:

package application;

import java.io.IOException;
import java.net.URL;
import java.util.ResourceBundle;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.fxml.Initializable;
import javafx.scene.control.Button;
import javafx.scene.control.ChoiceBox;
import javafx.scene.control.Label;
import javafx.scene.layout.AnchorPane;

public class BookController implements Initializable {

    @FXML
    private Button button;

    @FXML
    private AnchorPane scene1pane;

    @FXML
    private ChoiceBox<String> box;

    @FXML
    private AnchorPane scene2pane;

    @FXML
    private Label label;
    
    @FXML
    private Label label1;
    
    
    
    ObservableList<String> test = FXCollections.observableArrayList("AAA","BBB","CCC"); 
    
  
    public void initialize(URL arg0, ResourceBundle arg1) {
        // TODO Auto-generated method stub
        box.getItems().addAll(test);
        box.setOnAction(this::switchscene);
        
        
    }
    
    
    
  public  void switchscene(ActionEvent event)  {
        
        
        AnchorPane pane;
        try {
            pane = FXMLLoader.load(getClass().getResource("exscene2.fxml"));
            scene1pane.getChildren().setAll(pane);
            
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
    }
        
        String str = box.getValue();
        label.setText(str);
        
        
        }
    

}

My first scene fxml file:

<?xml version="1.0" encoding="UTF-8"?>

<?import javafx.scene.text.*?>
<?import javafx.scene.control.*?>
<?import java.lang.*?>
<?import javafx.scene.layout.*?>

<AnchorPane fx:id="scene1pane" maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="400.0" prefWidth="600.0" xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1" fx:controller="application.BookController">
   <children>
      <Button fx:id="button" layoutX="223.0" layoutY="162.0" mnemonicParsing="false" onAction="#switchscene" text="Button">
         <font>
            <Font size="36.0" />
         </font>
      </Button>
      <Label fx:id="label1" layoutX="139.0" layoutY="50.0" prefHeight="27.0" prefWidth="148.0" text="Scene 1">
         <font>
            <Font size="42.0" />
         </font>
      </Label>
      <ChoiceBox fx:id="box" layoutX="303.0" layoutY="31.0" prefWidth="150.0" />
   </children>
</AnchorPane>

My second scene fxml file:

<?xml version="1.0" encoding="UTF-8"?>

<?import javafx.scene.text.*?>
<?import javafx.scene.control.*?>
<?import java.lang.*?>
<?import javafx.scene.layout.*?>

<AnchorPane fx:id="scene2pane" maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="400.0" prefWidth="600.0" xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1" fx:controller="application.BookController">
   <children>
      <Label fx:id="label" layoutX="262.0" layoutY="92.0" text="Welcome">
         <font>
            <Font size="33.0" />
         </font>
      </Label>
   </children>
</AnchorPane>

Solution

There are many things to consider in this example. Frist, let me explain the errors which your are facing.

Firstly, on click of button or choosing the choice box, you are getting constructLoadException. This is because you are using the same Controller class for both the fxmls. And you are are expecting both the fxmls to share the same Controller instance. This will not be the case. With your code, each fxml will have its own instance of BookController. So in fxml1 controller, all the instance variables related to fxml2 will be null and vice versa.

So when you initiate the fxml2, a new instance of BookController is created and the initialize method is called. As there is no "box" node in fxml2, that variable will be null and obviously will throw NPE, which is causing the exception to load the fxml.

The second error of NPE is also same, this time you are expecting the fxml2 instance variable "label" in fxml1 controller.

Solution:

There are two ways to address this issue. It depends on whether you want to share the same Controller class or If you are ok to go with separate controller class for each fxml.

#1. Using same controller class

In this way, you need to do the below two changes.

Remove the controller declaration in the exscene2 fxml.
Change the initialize and switchScene methods as below. The main changes are we are setting the same controller instance manually to the fxml2 loader. And doing some checks in initialize method, to not re-add the items again.

public void initialize(URL arg0, ResourceBundle arg1) {
    if(box.getItems().isEmpty()) {
        box.getItems().addAll(test);
        box.setOnAction(this::switchscene);
    }
}

public void switchscene(ActionEvent event) {
    AnchorPane pane;
    try {
        // Initiate a loader for the fxml 2
        final FXMLLoader loader = new FXMLLoader(getClass().getResource("exscene2.fxml"));
        // Set this controller instance to fxml 2
        loader.setController(this);
        // And load the fxml 2.
        pane = loader.load();
        // By this line, both fxmls use same instance of controller
        scene1pane.getChildren().setAll(pane);
    } catch (IOException e) {
        e.printStackTrace();
    }

    String str = box.getValue();
    if(str!=null && !str.isEmpty()) {
        label.setText(str);
    }
}

#2. Using separate controller class

In this way, you need to do the below two changes.

Create a new Controller class for the fxml 2 (lets say BookController2.java) with instance variables that are only related to fxml 2.

import javafx.fxml.FXML;
import javafx.fxml.Initializable;
import javafx.scene.control.Label;
import javafx.scene.layout.AnchorPane;

import java.net.URL;
import java.util.ResourceBundle;

public class BookController2 implements Initializable {

    @FXML
    private AnchorPane scene2pane;

    @FXML
    private Label label;


    @Override
    public void initialize(URL url, ResourceBundle resourceBundle) {
        // Empty
    }

    public final Label getLabel(){
        return label;
    }
}

Set this BookController2 as controller in fxml 2.

fx:controller="application.BookController2"
In BookController.java remove all the instance variables of fxml 2 and change the switchScene method as below.

public void switchscene(ActionEvent event) {
    AnchorPane pane;
    try {
        // Initiate the loader for fxml 2. Using this loader, you can get the controller instance of fxml 2
        final FXMLLoader loader = new FXMLLoader(getClass().getResource("exscene2.fxml"));
        pane = loader.load();
        scene1pane.getChildren().setAll(pane);

        String str = box.getValue();
        if (str != null && !str.isEmpty()) {
            // Get the label from the controller and set the text.
            ((BookController2) loader.getController()).getLabel().setText(str);
        }
    } catch (IOException e) {
        e.printStackTrace();
    }
}

Answered By - Sai Dandem

This Answer collected from stackoverflow and tested by JavaFixing community admins, is licensed under cc by-sa 2.5 , cc by-sa 3.0 and cc by-sa 4.0

Thursday, December 23, 2021

[FIXED] JavaFX choice box null pointer exception while switching scene

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