为什么 If/Else 语句在第二个 else if 语句中不起作用？

Question

代码如下：

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){...}

上面的代码延续了类似的语句。

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.access00(Scene.java:3398)
    at javafx.scene.Scene$MouseHandler.process(Scene.java:3766)
    at javafx.scene.Scene$MouseHandler.access00(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$MouseEventNotification.run(GlassViewEventHandler.java:295)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent3(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$null7(WinApplication.java:177)
    at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:71)
    at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275)
    at javafx.fxml.FXMLLoader$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。所有代码似乎都有意义，但在程序的运行中不起作用。没看懂。

谢谢！

编辑摘要：我只是想澄清一下，我的 post 不是另一个的副本。至少我认为其他 post 的答案对我没有帮助。

Answer 1

假设确实如此

GridPane.getRowIndex(token17) == middleRow

或

GridPane.getColumnIndex(token17) == middleCol

引起问题的原因：

GridPane.getRowIndex 和 GridPane.getColumnIndex return 引用类型 Integer。对于未分配 row/column 索引的 Node，null 是 returned。尽管如此，这些节点可能是 GridPane 的子节点，使用 0 的默认值 row/column。

对 == 使用 Integer 和 int 操作数会产生与显式为 Integer 值调用 intValue() 方法相同的字节码。在 null 上调用此方法会导致出现异常。

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) {
    ...
}

为什么 If/Else 语句在第二个 else if 语句中不起作用？

Why is the If/Else statement not working at the second else if statement?

java

if-statement

javafx

gridpane