java - 使用 JavaFX set 和 get 方法时出现 InloggingTargetException

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("");
    }

}   

这会抛出一堆异常:

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

这是一个小型猜数游戏，创建一个随机数，然后与文本字段“eingabe”中的字符串进行比较。我明白为什么有时会抛出 NumberFormatException，但调用异常是全新的，我真的很希望得到一些帮助。

Answer 1

异常在最后说:

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

虽然我不知道它是哪一行，但调用 neuerVersuch 时会出现错误，并且它发现一个未初始化的字段，可能是 zahlenbereich。

原因是该字段(可能还有其他字段)未初始化，因为它未使用 @FXML 进行注释。如果这些是您的 FXML 文件中的控件，并且它们有 fx:id，您应该对它们进行注释:

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

因此，当加载 Controller 时，它们会被正确实例化。