java - 尝试使用 AnchorPane 的扩展版本时出现实例化和加载异常

Question

对于一个项目，我得到了代码并且必须将其重构为 FXML，我正在尝试使用我得到的一段代码，它是 AnchorPane 的扩展，但是当我在 FXML 中将其从 AnchorPane 切换到 World 时，我在场景生成器和运行它时出现错误。我已经尝试了很多东西，但有点困惑，现在不知道该尝试什么。我注释掉了 World 的原始构造函数，但如果可能相关，可以将其发布

世界:

package game;


import javafx.animation.AnimationTimer;
import javafx.scene.Node;
import javafx.scene.layout.AnchorPane;

import java.util.ArrayList;
import java.util.List;


public abstract class World extends AnchorPane {
    private AnimationTimer timer;

public void createTimer() {
        timer = new AnimationTimer() {
            @Override
            public void handle(long now) {
                act(now);
                List<Actor> actors = getObjects(Actor.class);

                for (Actor anActor: actors) {
                    anActor.act(now);
                }

            }
        };
    }

    public void start() {
        createTimer();
        timer.start();
    }

    public void stop() {
        timer.stop();
    }

    public void add(Actor actor) {
        getChildren().add(actor);
    }

    public void remove(Actor actor) {
        getChildren().remove(actor);
    }

    public <A extends Actor> List<A> getObjects(Class<A> cls) {
        ArrayList<A> someArray = new ArrayList<A>();
        for (Node n: getChildren()) {
            if (cls.isInstance(n)) {
                someArray.add((A)n);
            }
        }
        return someArray;
    }

    public abstract void act(long now);
}

FXML

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


<?import javafx.scene.image.*?>
<?import javafx.scene.layout.*?>


<?import game.End?>
<?import game.Log?>
<?import game.WetTurtle?>
<?import game.Turtle?>
<?import game.Obstacle?>
<?import game.World?>

<World maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity"
       prefHeight="800.0" prefWidth="600.0" xmlns="http://javafx.com/javafx/10.0.2-internal"
       xmlns:fx="http://javafx.com/fxml/1" fx:controller="game.Level1Controller">

   <ImageView>
      <image>
         <Image url="@../backgrounds/frogbg.png" />
      </image>
   </ImageView>
   <End layoutX="13.0" layoutY="138.8">
      <image>
         <Image url="@../end/End.png" />
      </image></End>
   <End layoutX="141.0" layoutY="138.0">
      <image>
         <Image url="@../end/End.png" />
      </image>
   </End>
   <End layoutX="269.0" layoutY="138.0">
      <image>
         <Image url="@../end/End.png" />
      </image>
   </End>
   <End layoutX="398.0" layoutY="138.0">
      <image>
         <Image url="@../end/End.png" />
      </image>
   </End>
   <End layoutX="528.0" layoutY="138.0">
      <image>
         <Image url="@../end/End.png" />
      </image>
   </End>
   <Log fitHeight="30.0" layoutY="209.0" pickOnBounds="true" preserveRatio="true">
      <image>
         <Image url="@../log/log3.png" />
      </image>
   </Log>
   <Log fitHeight="30.0" layoutX="220.0" layoutY="209.0" pickOnBounds="true" preserveRatio="true">
      <image>
         <Image url="@../log/log3.png" />
      </image>
   </Log>
   <Log fitHeight="30.0" layoutX="440.0" layoutY="209.0" pickOnBounds="true" preserveRatio="true">
      <image>
         <Image url="@../log/log3.png" />
      </image>
   </Log>
   <WetTurtle fitHeight="45.0" layoutX="600.0" layoutY="252.0" preserveRatio="true">
      <image>
         <Image url="@../turtle/TurtleAnimation1.png" />
      </image>
   </WetTurtle>
   <WetTurtle fitHeight="45.0" layoutX="400.0" layoutY="252.0" preserveRatio="true">
      <image>
         <Image url="@../turtle/TurtleAnimation1.png" />
      </image>
   </WetTurtle>
   <WetTurtle fitHeight="45.0" layoutX="200.0" layoutY="252.0" preserveRatio="true">
      <image>
         <Image url="@../turtle/TurtleAnimation1.png" />
      </image>
   </WetTurtle>
   <Log fitHeight="35.0" layoutY="308.0" pickOnBounds="true" preserveRatio="true">
      <image>
         <Image url="@../log/logs.png" />
      </image>
   </Log>
   <Log fitHeight="35.0" layoutX="440.0" layoutY="308.0" pickOnBounds="true" preserveRatio="true">
      <image>
         <Image url="@../log/logs.png" />
      </image>
   </Log>
   <Log fitHeight="35.0" layoutX="50.0" layoutY="358.0" pickOnBounds="true" preserveRatio="true">
      <image>
         <Image url="@../log/log3.png" />
      </image>
   </Log>
    <Log fitHeight="35.0" layoutX="270.0" layoutY="358.0" pickOnBounds="true" preserveRatio="true">
        <image>
            <Image url="@../log/log3.png" />
        </image>
    </Log>
   <Log fitHeight="35.0" layoutX="490.0" layoutY="358.0" pickOnBounds="true" preserveRatio="true">
      <image>
         <Image url="@../log/log3.png" />
      </image>
   </Log>
   <Turtle fitHeight="45.0" layoutX="500.0" layoutY="402.0" preserveRatio="true">
      <image>
         <Image url="@../turtle/TurtleAnimation1.png" />
      </image></Turtle>
   <Turtle fitHeight="45.0" layoutX="300.0" layoutY="402.0" preserveRatio="true">
      <image>
         <Image url="@../turtle/TurtleAnimation1.png" />
      </image>
   </Turtle>

   <WetTurtle fitHeight="45.0" layoutX="700.0" layoutY="402.0" preserveRatio="true">
      <image>
         <Image url="@../turtle/TurtleAnimation1.png" />
      </image>
   </WetTurtle>
   <Obstacle fitHeight="28.0" layoutX="500.0" layoutY="511.0" preserveRatio="true">
      <image>
         <Image url="@../car/car1Left.png" />
      </image>
   </Obstacle>
   <Obstacle fitHeight="35.0" layoutX="500.0" layoutY="557.0" preserveRatio="true">
      <image>
         <Image url="@../truck/truck2Right.png" />
      </image>
   </Obstacle>
   <Obstacle fitHeight="35.0" layoutY="557.0" preserveRatio="true">
      <image>
         <Image url="@../truck/truck2Right.png" />
      </image>
   </Obstacle>
   <Obstacle fitHeight="28.0" layoutX="550.0" layoutY="611.0" preserveRatio="true">
      <image>
         <Image url="@../car/car1Left.png" />
      </image>
   </Obstacle>
   <Obstacle fitHeight="28.0" layoutX="400.0" layoutY="611.0" preserveRatio="true">
      <image>
         <Image url="@../car/car1Left.png" />
      </image>
   </Obstacle>
   <Obstacle fitHeight="28.0" layoutX="250.0" layoutY="611.0" preserveRatio="true">
      <image>
         <Image url="@../car/car1Left.png" />
      </image>
   </Obstacle>
   <Obstacle fitHeight="28.0" layoutX="100.0" layoutY="611.0" preserveRatio="true">
      <image>
         <Image url="@../car/car1Left.png" />
      </image>
   </Obstacle>
   <Obstacle fitHeight="35.0" layoutX="600.0" layoutY="657.0" preserveRatio="true">
      <image>
         <Image url="@../truck/truck1Right.png" />
      </image>
   </Obstacle>
   <Obstacle fitHeight="35.0" layoutX="300.0" layoutY="657.0" preserveRatio="true">
      <image>
         <Image url="@../truck/truck1Right.png" />
      </image>
   </Obstacle>
   <Obstacle fitHeight="35.0" layoutY="657.0" preserveRatio="true">
      <image>
         <Image url="@../truck/truck1Right.png" />
      </image>
   </Obstacle>
</World>

错误

Exception in Application start method
java.lang.reflect.InvocationTargetException
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:564)
    at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:473)
    at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:372)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:564)
    at java.base/sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:941)
Caused by: java.lang.RuntimeException: Exception in Application start method
    at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:973)
    at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication$2(LauncherImpl.java:198)
    at java.base/java.lang.Thread.run(Thread.java:844)
Caused by: javafx.fxml.LoadException: 
/C:/Users/harry/IdeaProjects/Frogger%20Game/out/production/Frogger%20Game/game/fxml/level1.fxml:16

    at javafx.fxml/javafx.fxml.FXMLLoader.constructLoadException(FXMLLoader.java:2625)
    at javafx.fxml/javafx.fxml.FXMLLoader.access$700(FXMLLoader.java:105)
    at javafx.fxml/javafx.fxml.FXMLLoader$InstanceDeclarationElement.constructValue(FXMLLoader.java:1021)
    at javafx.fxml/javafx.fxml.FXMLLoader$ValueElement.processStartElement(FXMLLoader.java:754)
    at javafx.fxml/javafx.fxml.FXMLLoader.processStartElement(FXMLLoader.java:2722)
    at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2552)
    at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2466)
    at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3253)
    at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3210)
    at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3179)
    at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3152)
    at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3129)
    at javafx.fxml/javafx.fxml.FXMLLoader.load(FXMLLoader.java:3122)
    at Frogger.Game/game.Main.start(Main.java:25)
    at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$9(LauncherImpl.java:919)
    at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runAndWait$11(PlatformImpl.java:449)
    at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater$9(PlatformImpl.java:418)
    at java.base/java.security.AccessController.doPrivileged(Native Method)
    at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater$10(PlatformImpl.java:417)
    at javafx.graphics/com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:96)
    at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:175)
    ... 1 more
Caused by: java.lang.InstantiationException
    at java.base/jdk.internal.reflect.InstantiationExceptionConstructorAccessorImpl.newInstance(InstantiationExceptionConstructorAccessorImpl.java:48)
    at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:488)
    at java.base/java.lang.Class.newInstance(Class.java:560)
    at javafx.fxml/javafx.fxml.FXMLLoader$InstanceDeclarationElement.constructValue(FXMLLoader.java:1019)
    ... 20 more
Exception running application game.Main

Process finished with exit code 1

Answer 1

World 是抽象的，您无法构造抽象类的实例。

当你声明一个元素时:

<World ...>

在 FXML 中，当您加载 FXML 文档时，FXMLLoader 将尝试创建 World 类的实例。当它这样做时，它会失败，因为 World 是抽象的并且无法实例化。

您的代码或设计中可能还存在其他问题，但至少存在此处指出的问题。

if i want to make an instance of it but it extend AnchorPane how do i go about that?

你不能，你的类层次结构已经由你的 extends 子句定义了，除非你改变层次结构设计(例如重新编码 World 所以它不是抽象的)，你必须实例化 World 的具体子类。

I have another class that extends world that isn't abstract so i should use that instead i guess?

是的。