为什么If / Else语句在第二个else if语句处不起作用？

Question

这是代码：

if(GridPane.getRowIndex(token1) == middleRow && GridPane.getColumnIndex(token1) == middleCol){
    mainGrid.getChildren().remove(token1);
        } else if(GridPane.getRowIndex(token17) == middleRow && GridPane.getColumnIndex(token17) == middleCol){
                mainGrid.getChildren().remove(token17);
        } else if(GridPane.getRowIndex(token3) == middleRow && GridPane.getColumnIndex(token3) == middleCol){
                mainGrid.getChildren().remove(token3);
        } else if(GridPane.getRowIndex(token4) == middleRow && GridPane.getColumnIndex(token4) == middleCol){
                mainGrid.getChildren().remove(token4);
        } else if(GridPane.getRowIndex(token5) == middleRow && GridPane.getColumnIndex(token5) == middleCol){
                mainGrid.getChildren().remove(token5);
        } else if(GridPane.getRowIndex(token6) == middleRow && GridPane.getColumnIndex(token6) == middleCol){...}

上面的代码继续执行类似的语句。

这是错误：

Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
    at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1774)
    at javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1657)
    at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
    at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
    at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
    at javafx.event.Event.fireEvent(Event.java:198)
    at javafx.scene.Scene$ClickGenerator.postProcess(Scene.java:3470)
    at javafx.scene.Scene$ClickGenerator.access$8100(Scene.java:3398)
    at javafx.scene.Scene$MouseHandler.process(Scene.java:3766)
    at javafx.scene.Scene$MouseHandler.access$1500(Scene.java:3485)
    at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1762)
    at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2494)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:394)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:295)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$353(GlassViewEventHandler.java:432)
    at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:431)
    at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
    at com.sun.glass.ui.View.notifyMouse(View.java:937)
    at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at com.sun.glass.ui.win.WinApplication.lambda$null$147(WinApplication.java:177)
    at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:71)
    at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275)
    at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1771)
    ... 31 more
Caused by: java.lang.NullPointerException
    at sudoku.FXMLDocumentController.removeMiddleToken(FXMLDocumentController.java:166)
    at sudoku.FXMLDocumentController.moveToken(FXMLDocumentController.java:162)
    at sudoku.FXMLDocumentController.isMoveLegal(FXMLDocumentController.java:151)
    at sudoku.FXMLDocumentController.square33Click(FXMLDocumentController.java:447)
    ... 41 more

错误从第一个“ if”语句之后的第一个“ else if”语句开始。 所有的代码似乎都有意义，但在程序运行时不起作用。 我不明白。

谢谢！

编辑摘要：我只想澄清一下，我的帖子与其他文章没有重复。 至少我不认为其他帖子的答案对我有帮助。

Answer 1

假设确实

GridPane.getRowIndex(token17) == middleRow

要么

GridPane.getColumnIndex(token17) == middleCol

引起问题：

GridPane.getRowIndex和GridPane.getColumnIndex返回引用类型Integer 。 对于未分配行/列索引的Node ，返回null 。 但是，使用默认行/列0 ，这些节点仍可以是GridPane子级。

将Integer和int操作数用于==产生与显式调用intValue()方法以获取Integer值相同的字节码。 在null上调用此方法将导致您得到异常。

else if (GridPane.getRowIndex(token17).intValue() == middleRow
    && GridPane.getColumnIndex(token17).intValue() == middleCol) {
    ...
}

使用以下方法将Integer转换为int应该可以解决此问题：

public static int toIndex(Integer value) {
    return value == null ? 0 : value.intValue();
}

else if (toIndex(GridPane.getRowIndex(token17)) == middleRow
    && toIndex(GridPane.getColumnIndex(token17)) == middleCol) {
    ...
}