使用JavaFX set和get方法时InvocationTargetException

Question

    //Max Maier, Milan Radovanovic
package application;
import javafx.fxml.FXML;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.control.TextField;
public class Control {
    private static int anz = 1;
    int generierteZahl = (int) Math.ceil(Math.random()*100);
    Label anzversuche;
    Label zahlenbereich;
    Button ratenb;
    TextField eingabe;
    @FXML void raten(){ 
        if (generierteZahl == Integer.parseInt(eingabe.getText())){
            anzversuche.setText(anz + ". Versuche");
            ratenb.setDisable(true);
            zahlenbereich.setText("Richtig geraten!!!");
        }
        else if (generierteZahl > Integer.parseInt(eingabe.getText())){
            anz++;
            anzversuche.setText(anz + ". Versuche");
            zahlenbereich.setText(Integer.parseInt(eingabe.getText()) + " ist zu klein");
        }
        else{
            anzversuche.setText(anz + ". Versuche");
            zahlenbereich.setText(Integer.parseInt(eingabe.getText()) + " ist zu groß");
        }
        anz++;
    }
    @FXML void neuerVersuch(){
        anz = 1;
        generierteZahl = (int) Math.ceil(Math.random()*100);
        zahlenbereich.setText("Noch keine Zahl eingegeben");
        anzversuche.setText(anz + ". Versuche");
        ratenb.setDisable(false);
        eingabe.setText("");
    }

}   

如果出现异常，则会发出一堆提示：

Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
    at javafx.fxml.FXMLLoader$MethodHandler.invoke(Unknown Source)
    at javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(Unknown Source)
    at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(Unknown Source)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source)
    at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(Unknown Source)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.EventUtil.fireEventImpl(Unknown Source)
    at com.sun.javafx.event.EventUtil.fireEvent(Unknown Source)
    at javafx.event.Event.fireEvent(Unknown Source)
    at javafx.scene.Node.fireEvent(Unknown Source)
    at javafx.scene.control.Button.fire(Unknown Source)
    at com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(Unknown Source)
    at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(Unknown Source)
    at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(Unknown Source)
    at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(Unknown Source)
    at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(Unknown Source)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source)
    at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(Unknown Source)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.EventUtil.fireEventImpl(Unknown Source)
    at com.sun.javafx.event.EventUtil.fireEvent(Unknown Source)
    at javafx.event.Event.fireEvent(Unknown Source)
    at javafx.scene.Scene$MouseHandler.process(Unknown Source)
    at javafx.scene.Scene$MouseHandler.access$1500(Unknown Source)
    at javafx.scene.Scene.impl_processMouseEvent(Unknown Source)
    at javafx.scene.Scene$ScenePeerListener.mouseEvent(Unknown Source)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(Unknown Source)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(Unknown Source)
    at com.sun.glass.ui.View.handleMouseEvent(Unknown Source)
    at com.sun.glass.ui.View.notifyMouse(Unknown Source)
    at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at com.sun.glass.ui.win.WinApplication.lambda$null$141(Unknown Source)
    at com.sun.glass.ui.win.WinApplication$$Lambda$37/1109371569.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at sun.reflect.misc.Trampoline.invoke(Unknown Source)
    at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at sun.reflect.misc.MethodUtil.invoke(Unknown Source)
    ... 48 more
Caused by: java.lang.NullPointerException
    at application.Control.neuerVersuch(Control.java:34)
    ... 57 more

这是一款猜数字的小游戏，其中会创建一个随机数，然后将其与文本字段“ eingabe”中的String进行比较。 我知道为什么有时会引发NumberFormatException，但是invoke异常是全新的，我真的很感谢您的帮助。

Answer 1

异常在末尾说：

Caused by: java.lang.NullPointerException
at application.Control.neuerVersuch(Control.java:34)

尽管我不清楚这是哪行，但是在neuerVersuch时出现错误，并且它找到未初始化的字段，可能是zahlenbereich 。

原因是此字段（可能还有其他字段）没有被实例化，因为它没有使用@FXML注释。 如果thouse是FXML文件中的控件，并且它们具有fx:id ，则应为它们添加注释：

@FXML Label anzversuche;
@FXML Label zahlenbereich;
@FXML Button ratenb;
@FXML TextField eingabe;

因此，在加载控制器时，将它们正确实例化。