如何在没有实例化异常的情况下将此超类更改为抽象类？

Question

我想使我的超类成为抽象类，但是尝试这样做时会遇到各种异常（InstantiationException，RuntimeException，InvocationTargetException）。当我没有超类作为抽象时，我的代码将起作用。我该如何解决？

我已经尝试将我的“ main”和“ start”函数包括在抽象类主体之外，因为我认为在抽象类内部调用这些函数可能是一个问题。我将这些方法移到扩展抽象类的子类中。然后，我覆盖了每个子类中的抽象方法“ start”。重新格式化并没有解决任何问题，因为我遇到了相同的错误。根据我对这个问题How do you call a subclass method from a superclass in Java?的研究，该用户使用的格式接近于我的抽象超类扩展“应用程序”所试图实现的格式。

package tutorial.application;

import javafx.application.Application;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.canvas.Canvas;
import javafx.scene.canvas.GraphicsContext;
import javafx.stage.Stage;
import javafx.scene.paint.Color;
import java.lang.Math;


public abstract class Test extends Application{

    private int width = 0;
    private int height = 0;

    public Test() {
        this.width = 0;
        this.height = 0;
    }

    public Test(int width, int height) {
        this.width = width;
        this.height = height;
    }

    public abstract void draw(GraphicsContext GC);


    public class MyLine extends Test{

        private int x1, x2, y1, y2;

        public MyLine(int x1, int y1, int x2, int y2) {
            super(0, 0);
            this.x1 = x1;
            this.x2 = x2;
            this.y1 = y1;
            this.y2 = y2;
        }

        @Override
        public void draw(GraphicsContext GC){
            GC.strokeLine(x1, y1, x2, y2);
        }
    }

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

    @Override
    public void start(Stage primaryStage) {

        int canvasx = 400, canvasy = 650;
        MyLine line = new MyLine(0, 0, canvasx, canvasy);
        MyLine line2 = new MyLine(0, canvasy, canvasx, 0);
        Group root = new Group();
        Canvas canvas = new Canvas(canvasx, canvasy);
        GraphicsContext GC = canvas.getGraphicsContext2D();
        line.draw(GC);
        line2.draw(GC);
        root.getChildren().add(canvas);
        primaryStage.setScene(new Scene(root));
        primaryStage.show();
    }

}
[当我没有超类作为抽象类并且draw不再是抽象方法时，我得到了它，这是我想要的输出：https://i.imgur.com/J4XB8bo.png

但是，否则我收到以下错误消息：

Exception in Application constructor
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:567)
    at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:464)
    at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:363)
    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:567)
    at java.base/sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:1051)
Caused by: java.lang.RuntimeException: Unable to construct Application instance: class tutorial.application.Test
    at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:890)
    at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication$2(LauncherImpl.java:195)
    at java.base/java.lang.Thread.run(Thread.java:835)
Caused by: java.lang.InstantiationException
    at java.base/jdk.internal.reflect.InstantiationExceptionConstructorAccessorImpl.newInstance(InstantiationExceptionConstructorAccessorImpl.java:48)
    at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:500)
    at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:481)
    at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$8(LauncherImpl.java:802)
    at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runAndWait$12(PlatformImpl.java:455)
    at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater$10(PlatformImpl.java:428)
    at java.base/java.security.AccessController.doPrivileged(AccessController.java:389)
    at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater$11(PlatformImpl.java:427)
    at javafx.graphics/com.sun.glass.ui.InvokeLaterDispatcher$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:174)
    ... 1 more
Exception running application tutorial.application.Test
编辑：到目前为止，我已经尝试了大约3种明显不同的选项，所有选项均导致错误。首先，我尝试从层次结构中将子类设为静态，如下所示：

static class MyLine extends Test{
.
.
.
}
我还再次尝试将内部类“ MyLine”从超类“ Test”中移除，如下所示：

public abstract class Test extends Application{

    private int width = 0;
    private int height = 0;

    public Test() {
        this.width = 0;
        this.height = 0;
    }

    public Test(int width, int height) {
        this.width = width;
        this.height = height;
    }

    public abstract void draw(GraphicsContext GC);

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

    @Override
    public void start(Stage primaryStage) {

        int canvasx = 400, canvasy = 650;
        MyLine line = new MyLine(0, 0, canvasx, canvasy);
        MyLine line2 = new MyLine(0, canvasy, canvasx, 0);
        Group root = new Group();
        Canvas canvas = new Canvas(canvasx, canvasy);
        GraphicsContext GC = canvas.getGraphicsContext2D();
        line.draw(GC);
        line2.draw(GC);
        root.getChildren().add(canvas);
        primaryStage.setScene(new Scene(root));
        primaryStage.show();
    }
}

class MyLine extends Test{

    private int x1, x2, y1, y2;

    public MyLine(int x1, int y1, int x2, int y2) {
        super(0, 0);
        this.x1 = x1;
        this.x2 = x2;
        this.y1 = y1;
        this.y2 = y2;
    }

    @Override
    public void draw(GraphicsContext GC){
        GC.strokeLine(x1, y1, x2, y2);
    }
}
Laslty我设计了一个新的类“ Main”来扩展“ Test”并从那里启动应用程序，如下所示：

package tutorial.application;

import javafx.application.Application;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.canvas.Canvas;
import javafx.scene.canvas.GraphicsContext;
import javafx.stage.Stage;
import javafx.scene.paint.Color;
import java.lang.Math;


public abstract class Test extends Application{

    private int width = 0;
    private int height = 0;

    public Test() {
        this.width = 0;
        this.height = 0;
    }

    public Test(int width, int height) {
        this.width = width;
        this.height = height;
    }

    public abstract void draw(GraphicsContext GC);


}

class MyLine extends Test{

    private int x1, x2, y1, y2;

    public MyLine(int x1, int y1, int x2, int y2) {
        super(0, 0);
        this.x1 = x1;
        this.x2 = x2;
        this.y1 = y1;
        this.y2 = y2;
    }

    @Override
    public void draw(GraphicsContext GC){
        GC.strokeLine(x1, y1, x2, y2);
    }

    @Override
    public void start(Stage arg0) throws Exception {

    }
}

class Main extends Test{
    private Main() {
        super(0,0);
    }
    public static void main(String []args){
        launch(args);
    }

    @Override
    public void start(Stage primaryStage) {

        int canvasx = 400, canvasy = 650;
        MyLine line = new MyLine(0, 0, canvasx, canvasy);
        MyLine line2 = new MyLine(0, canvasy, canvasx, 0);
        Group root = new Group();
        Canvas canvas = new Canvas(canvasx, canvasy);
        GraphicsContext GC = canvas.getGraphicsContext2D();
        line.draw(GC);
        line2.draw(GC);
        root.getChildren().add(canvas);
        primaryStage.setScene(new Scene(root));
        primaryStage.show();
    }

    @Override
    public void draw(GraphicsContext GC) {

    }
}
[前两个仍然会导致相同的错误，而我认为最后一个会加剧我的问题，因为它在线程“ main”中引发了新的异常：

Exception in thread "main" java.lang.reflect.InvocationTargetException

我想使我的超类成为抽象类，但是尝试这样做时会遇到各种异常（InstantiationException，RuntimeException，InvocationTargetException）。当我...

Answer 1

如果超类是抽象的，则无法实例化子类的原因是，子类是超类的inner

Answer 2

我通过将我的类文件重命名为“ Main”找到了可行的解决方案。这使我得以保留抽象类“ Test”及其所​​有子类，并通过扩展了“应用程序”的新公共类“ Main”启动了应用程序。