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What is a NullPointerException, and how do I fix it?
                                
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                                3年前关闭。
            
                    
我希望我的进度栏显示返回双精度值的方法的值,但它不起作用。但是我不认为这是主要的问题,即使我只是使用一个特定的数字,它也不起作用。请帮助我,在此先感谢。那是一个特定的问题,所以我搜索了很长时间而没有结果,所以如果您知道做我想做的事更好,或者知道一个可以帮助您链接或告诉我的网站。

我的fxml文件的控制器(已标记相关代码):

package sample;

import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.ProgressBar;
import javafx.scene.image.Image;
import javafx.scene.image.ImageView;
import javafx.scene.layout.Pane;
import javafx.stage.Stage;
import javafx.event.EventHandler;
import javafx.scene.input.MouseEvent;
import java.io.IOException;
import java.util.ResourceBundle;
import java.util.ArrayList;
import java.util.Random;

public class Controller {

    playercard iceborn = new playercard(3, false, true, 0);
    playercard fireball = new playercard(5, true, false, 0);
    playercard warmogs = new playercard(0, false, false, 10);

    ArrayList<playercard> playerhand = new ArrayList<>();
    *******************************
    public void add() {
        playerhand.add(iceborn);
        playerhand.add(fireball);
        playerhand.add(warmogs);
    }

    public playercard output() {
        Random rand = new Random();
        int xzufallszahl = rand.nextInt(3);
        int zufallszahl = xzufallszahl;
        return playerhand.get(zufallszahl);
    }
    *********************************
    @FXML
    Stage stage;
    public Button Startgameb;

    @FXML
    public ProgressBar enemyhpnow;


    @FXML
    public void Startgamebaction(ActionEvent event) throws IOException{
        ***************
        add();
        **************
        Parent root = FXMLLoader.load(getClass().getResource("Menu.fxml"));
        Pane root1 =  FXMLLoader.load(getClass().getResource("Tutorial.fxml"));
        Pane root2 = FXMLLoader.load(getClass().getResource("Game.fxml"));
        Scene tutorialscene = new Scene(root1, 900, 600);
        Scene gamescene = new Scene(root2, 900, 600);

        Image card = new Image("sample/card.jpg");
        ImageView firstplayercard = new ImageView();
        firstplayercard.setImage(card);
        firstplayercard.setFitWidth(120);
        firstplayercard.setFitHeight(160);
        firstplayercard.setLayoutX(50);
        firstplayercard.setLayoutY(430);

        ImageView secondplayercard = new ImageView();
        secondplayercard.setImage(card);
        secondplayercard.setFitWidth(120);
        secondplayercard.setFitHeight(160);
        secondplayercard.setLayoutX(175);
        secondplayercard.setLayoutY(430);

        ImageView thirdplayercard = new ImageView();
        thirdplayercard.setImage(card);
        thirdplayercard.setFitWidth(120);
        thirdplayercard.setFitHeight(160);
        thirdplayercard.setLayoutX(300);
        thirdplayercard.setLayoutY(430);

        ImageView fourthplayercard = new ImageView();
        fourthplayercard.setImage(card);
        fourthplayercard.setFitWidth(120);
        fourthplayercard.setFitHeight(160);
        fourthplayercard.setLayoutX(425);
        fourthplayercard.setLayoutY(430);

        ImageView fifthplayercard = new ImageView();
        fifthplayercard.setImage(card);
        fifthplayercard.setFitWidth(120);
        fifthplayercard.setFitHeight(160);
        fifthplayercard.setLayoutX(550);
        fifthplayercard.setLayoutY(430);

        root2.getChildren().addAll(firstplayercard, secondplayercard, thirdplayercard, fourthplayercard, fifthplayercard);
        **********************************
        firstplayercard.setOnMouseClicked(e ->{
            enemyhpnow.setProgress(output().activate());
        });
        **********************************
        Stage stage;
        stage=(Stage) Startgameb.getScene().getWindow();
        stage.setScene(gamescene);
        stage.show();
    }
}


那是我制作要使用其值的对象的类:

package sample;
import javafx.fxml.FXML;
import javafx.scene.control.ProgressBar;

public class playercard {
    int dmgovertime;
    boolean fire;
    boolean ice;
    int getlife;
    int playerhp = 100;
    int enemyhp = 300;


    public playercard(int dmgovertime, boolean fire, boolean ice, int getlife) {
        this.dmgovertime = dmgovertime;
        this.fire = fire;
        this.ice = ice;
        this.getlife = getlife;
    }

    public double activate(){
        enemyhp = enemyhp - dmgovertime + getlife;
        double xenemyhp = enemyhp;
        System.out.println(enemyhp);
        return xenemyhp;
    }
}


那是我的fxml文件(相关的文件):

<?xml version="1.0" encoding="UTF-8"?>

<?import javafx.scene.text.*?>
<?import javafx.scene.image.*?>
<?import javafx.scene.shape.*?>
<?import javafx.scene.control.*?>
<?import java.lang.*?>
<?import javafx.scene.layout.*?>
<?import javafx.geometry.Insets?>
<?import javafx.scene.layout.GridPane?>
<?import javafx.scene.control.Button?>
<?import javafx.scene.control.Label?>

<Pane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="600.0" prefWidth="900.0" styleClass="hintergrund1" stylesheets="@style.css" xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1">
   <children>
      <ProgressBar fx:id="playerhp" layoutX="100.0" layoutY="20.0" prefHeight="20.0" prefWidth="700.0" progress="0.87" />
      <Label layoutX="425.0" layoutY="-14.0" prefHeight="50.0" prefWidth="50.0" text="100 HP" />
      <ImageView fitHeight="351.0" fitWidth="373.0" layoutX="273.0" layoutY="40.0" pickOnBounds="true" preserveRatio="true">
         <image>
            <Image url="@enemy.png" />
         </image>
      </ImageView>
      <Label layoutX="812.0" layoutY="15.0" prefHeight="50.0" prefWidth="66.0" text="1/3" />
      <Label layoutX="14.0" layoutY="11.0" prefHeight="59.0" prefWidth="77.0" text="1/5" />
      <ProgressBar fx:id="enemyhpnow" layoutX="283.0" layoutY="391.0" prefHeight="31.0" prefWidth="353.0" progress="0.75" />
      <Label layoutX="431.0" layoutY="374.0" text="250 HP" />
      <ImageView fitHeight="160.0" fitWidth="120.0" layoutX="758.0" layoutY="422.0" pickOnBounds="true" preserveRatio="true">
         <image>
            <Image url="@carddeck.png" />
         </image>
      </ImageView>
   </children>
</Pane>


我的主:

package sample;

import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.image.Image;
import javafx.scene.image.ImageView;
import javafx.scene.layout.Pane;
import javafx.stage.Stage;

public class Main extends Application {

    public static void main(String[] args) {
        launch(args);
    }

    @Override
    public void start(Stage primaryStage) throws Exception{
        Parent root = FXMLLoader.load(getClass().getResource("Menu.fxml"));
        Scene menuscene = new Scene(root, 900, 600);

        primaryStage.setTitle("Project: Spark!");
        primaryStage.setScene(menuscene);
        primaryStage.show();
    }

}


那就是我对敌人hpnow.setProgress(output()。activate())的错误;从我的控制器:

Exception in thread "JavaFX Application Thread" java.lang.NullPointerException
    at sample.Controller.lambda$Startgamebaction$0(Controller.java:100)
    at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
    at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
    at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
    at javafx.event.Event.fireEvent(Event.java:198)
    at javafx.scene.Scene$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$MouseEventNotification.run(GlassViewEventHandler.java:380)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:294)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$354(GlassViewEventHandler.java:416)
    at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:415)
    at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
    at com.sun.glass.ui.View.notifyMouse(View.java:937)
    at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at com.sun.glass.ui.win.WinApplication.lambda$null$148(WinApplication.java:191)
    at java.lang.Thread.run(Thread.java:745)

Process finished with exit code 0


那就是我使用敌人hpnow.setProgress(1)时的错误代码;也在我的控制器中:

Exception in thread "JavaFX Application Thread" java.lang.NullPointerException
    at sample.Controller.lambda$Startgamebaction$0(Controller.java:100)
    at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
    at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
    at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
    at javafx.event.Event.fireEvent(Event.java:198)
    at javafx.scene.Scene$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$MouseEventNotification.run(GlassViewEventHandler.java:380)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:294)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$354(GlassViewEventHandler.java:416)
    at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:415)
    at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
    at com.sun.glass.ui.View.notifyMouse(View.java:937)
    at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at com.sun.glass.ui.win.WinApplication.lambda$null$148(WinApplication.java:191)
    at java.lang.Thread.run(Thread.java:745)

Process finished with exit code 0

最佳答案

您忘记定义Controller了,我在代码fxml的任何地方都看不到它:

fx:controller="yourController"

09-10 09:48
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