java - 运行 ArrayList 时抛出空指针异常

Question

我试图获取选定的复选框，并基于此通过以下代码获取一些值。但当我运行它时它会抛出空指针异常。请让我知道如何解决它。

public class GenController implements Initializable {

    @FXML
    private Button Generate;

    @FXML
    private CheckBox lows;
    private CheckBox caps;
    private CheckBox numb;
    private CheckBox sp;
    private CheckBox mcp;

    ArrayList<CheckBox> boxes = new ArrayList<CheckBox>();
    ArrayList<CheckBox> selected;


    public void buttonPressedGen(ActionEvent event) throws Exception {


        for (int i = 0; i < boxes.size(); i++) {
            if (boxes.get(i).isSelected()) {
                System.out.println(boxes.get(i).getText());
            }
        }

    }


    @Override
    public void initialize(URL location, ResourceBundle resources) {
        // TODO Auto-generated method stub
        boxes.add(lows);
        boxes.add(caps);
        boxes.add(numb);
        boxes.add(sp);
        boxes.add(mcp);
    }

}

错误:

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$1800(Unknown Source)
    at javafx.scene.Scene.impl_processMouseEvent(Unknown Source)
    at javafx.scene.Scene$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.access$300(Unknown Source)
    at com.sun.glass.ui.win.WinApplication$4$1.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 key.management.techcert.GenController.buttonPressedGen(GenController.java:54)
    ... 57 more

Answer 1

您需要注释每个单独的 CheckBox 引用，以便 FXMLLoader 注入(inject)它们:

@FXML
private CheckBox lows;
@FXML
private CheckBox caps;
@FXML
private CheckBox numb;
@FXML
private CheckBox sp;
@FXML
private CheckBox mcp;

如您所见，caps、numb 等都是null。