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在将字符串从一个类传递到另一个类中的函数时，我得到了 NullPointerException。我不完全明白什么是错的。我还试图确保我传递的字符串是否为空。但它不是空的..

异常指出的行和调用 AMCHelpEditor 中的函数的行如下（此代码中的错误在最后一行：原始代码的 125）：

String s = AMCImage.getSmellFromAMC(file);
System.out.print(s);
System.out.print(s.isEmpty());
System.out.print(SMCImage.getSmellFromAMC(f));
GridPane grid = sm.AMCEdit(s);

另外，AMCEditor中AMCEdit的功能代码为：

public GridPane AMCEdit(String s){
  amc = am.readAllAmcName();
  AMCBean sb2 = new AMCBean();
  AMCAccessor sa = new AMCAccessor();
  sb2 = sa.getAllAmcInfoById(s); 
  String name = sb2.getAmcName();
    gridPane.setPadding(new Insets(20, 0, 20, 20));
    gridPane.setHgap(7); gridPane.setVgap(7);

    Label amc1 = new Label("Select AMC :");
    GridPane.setHalignment(smell1, HPos.RIGHT);


    cb = new ChoiceBox();
    cb.setItems(FXCollections.observableArrayList(amc));
    cb.getSelectionModel().select(name);



    cb.valueProperty().addListener(new ChangeListener() {
         @Override
        public void changed(ObservableValue observable, Object oldValue,
            Object newValue) {
            text =cb.getValue().toString();
            xyz = sm.getAllAmcInfoByName(text);
             descptn = xyz.getAmcDesc().toString();
             frmla = xyz.getAmcChemFormula().toString();
             am = xyz.getAmcId();
             setAmc(am);
             tfdesc = new TextField(descptn);          
             tffrml = new TextField(frmla);
            }
    });


     gridPane.add(amc1, 0, 0);
     gridPane.add(cb, 1, 0);

      gridPane.getColumnConstraints().addAll(
        new ColumnConstraints(150),
        new ColumnConstraints(200)
    );
            gridPane.getRowConstraints().addAll(
           new RowConstraints(30),
           new RowConstraints(), // scale
           new RowConstraints(30),
           new RowConstraints(),
           new RowConstraints(30),
           new RowConstraints(),
           new RowConstraints(30)

     );

     return gridPane;

}

显示为系统输出的错误是：

java.lang.NullPointerException
    at com.smell.component.AMCEditor.AMCEdit(AMCEditor.java:125)
    at com.smell.component.AMCHelpEditor.getTab(AMCHelpEditor.java:74)
    at com.smell.modules.ImageApi$1$1$1.handle(ImageApi.java:100)
    at com.smell.modules.ImageApi$1$1$1.handle(ImageApi.java:96)
    at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:69)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:217)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:170)
    at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:38)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:37)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
    at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:53)
    at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:28)
    at javafx.event.Event.fireEvent(Event.java:171)
    at javafx.scene.Node.fireEvent(Node.java:6863)
    at javafx.scene.control.Button.fire(Button.java:179)
    at com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:193)
    at com.sun.javafx.scene.control.skin.SkinBase$4.handle(SkinBase.java:336)
    at com.sun.javafx.scene.control.skin.SkinBase$4.handle(SkinBase.java:329)
    at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:64)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:217)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:170)
    at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:38)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:37)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
    at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:53)
    at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:33)
    at javafx.event.Event.fireEvent(Event.java:171)
    at javafx.scene.Scene$MouseHandler.process(Scene.java:3324)
    at javafx.scene.Scene$MouseHandler.process(Scene.java:3164)
    at javafx.scene.Scene$MouseHandler.access$1900(Scene.java:3119)
    at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1559)
    at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2261)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:228)
    at com.sun.glass.ui.View.handleMouseEvent(View.java:528)
    at com.sun.glass.ui.View.notifyMouse(View.java:922)
    at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at com.sun.glass.ui.win.WinApplication.access$100(WinApplication.java:29)
    at com.sun.glass.ui.win.WinApplication$2$1.run(WinApplication.java:67)
    at java.lang.Thread.run(Thread.java:722)
'201''201'false'201'Exception in thread "JavaFX Application Thread" jfxsa-run:

系统输出符合预期。（请参阅错误的最后几行）。如果字符串不为 Null，则

您能否指出错误或提出替代方案？

4

1 回答 1

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I would suggest the that rather than checking the string for null, put a null check for your sm object

sm.AMCEdit(s);

Here your sm object might not have been initialized and then trying to invoke a method on uninitialized sm will result in NPE

So make sure you have initialzed it.

于 2013-07-28T05:37:00.243 回答