显示3个随机卡JavaFX

Question

所以基本上挑战在于标题。这是非常基本的，但我想我已经掌握了大部分内容。我遇到的一个问题是卡片的图片来自哪里。我知道通常你会把它们从你的计算机中拿出来，但是我正在这样做，其中的图片来自网址。这是我到目前为止，但我得到了一系列错误（InvocationTargetException，Runtime和IndexOutOfBounds）任何帮助表示赞赏。

import java.util.ArrayList;
import javafx.application.Application;
import javafx.stage.Stage;
import javafx.scene.Scene;
import javafx.scene.image.ImageView;
import javafx.scene.image.Image;
import javafx.scene.layout.HBox;
public class Exercise14_03 extends Application{
    @Override
    public void start(Stage primaryStage){
        ArrayList<String> cards = new ArrayList<>();

        for(int i = 0; i < 52; i++){
            cards.add(String.valueOf(i + 1));

        java.util.Collections.shuffle(cards);

        ImageView view1 = new ImageView(new Image("https://liveexample.pearsoncmg.com/book/image/card/" + cards.get(0) + ".png"));
        ImageView view2 = new ImageView(new Image("https://liveexample.pearsoncmg.com/book/image/card/" + cards.get(1) + ".png"));
        ImageView view3 = new ImageView(new Image("https://liveexample.pearsoncmg.com/book/image/card/" + cards.get(2) + ".png"));

        HBox root = new HBox();

        root.getChildren().add(view1);
        root.getChildren().add(view2);
        root.getChildren().add(view3);

        Scene scene = new Scene(root);

        primaryStage.setTitle("Exercise14_03");
        primaryStage.setScene(scene);
        primaryStage.show();
        }
    }

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

（例外）

Exception in Application start method
java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:389)
    at com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:328)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:767)
Caused by: java.lang.RuntimeException: Exception in Application start method
    at com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:917)
    at com.sun.javafx.application.LauncherImpl.lambda$launchApplication$155(LauncherImpl.java:182)
    at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.IndexOutOfBoundsException: Index: 1, Size: 1
    at java.util.ArrayList.rangeCheck(ArrayList.java:653)
    at java.util.ArrayList.get(ArrayList.java:429)
    at Exercise14_03.start(Exercise14_03.java:29)
    at com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$162(LauncherImpl.java:863)
    at com.sun.javafx.application.PlatformImpl.lambda$runAndWait$175(PlatformImpl.java:326)
    at com.sun.javafx.application.PlatformImpl.lambda$null$173(PlatformImpl.java:295)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.application.PlatformImpl.lambda$runLater$174(PlatformImpl.java:294)
    at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
    at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at com.sun.glass.ui.win.WinApplication.lambda$null$148(WinApplication.java:191)

Answer 1

人们使用样式指南进行缩进等原因是它减少了出错的可能性。如果你拿走你的代码：

import java.util.ArrayList;
import javafx.application.Application;
import javafx.stage.Stage;
import javafx.scene.Scene;
import javafx.scene.image.ImageView;
import javafx.scene.image.Image;
import javafx.scene.layout.HBox;
public class Exercise14_03 extends Application{
    @Override
    public void start(Stage primaryStage){
        ArrayList<String> cards = new ArrayList<>();

        for(int i = 0; i < 52; i++){
            cards.add(String.valueOf(i + 1));

        java.util.Collections.shuffle(cards);

        ImageView view1 = new ImageView(new Image("https://liveexample.pearsoncmg.com/book/image/card/" + cards.get(0) + ".png"));
        ImageView view2 = new ImageView(new Image("https://liveexample.pearsoncmg.com/book/image/card/" + cards.get(1) + ".png"));
        ImageView view3 = new ImageView(new Image("https://liveexample.pearsoncmg.com/book/image/card/" + cards.get(2) + ".png"));

        HBox root = new HBox();

        root.getChildren().add(view1);
        root.getChildren().add(view2);
        root.getChildren().add(view3);

        Scene scene = new Scene(root);

        primaryStage.setTitle("Exercise14_03");
        primaryStage.setScene(scene);
        primaryStage.show();
        }
    }

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

并正确缩进（大多数IDE都会为您执行此操作，例如在Eclipse中您可以使用CTRL-A选择所有内容，然后使用CTRL-SHIFT-F对其进行格式化），您将获得

import java.util.ArrayList;
import javafx.application.Application;
import javafx.stage.Stage;
import javafx.scene.Scene;
import javafx.scene.image.ImageView;
import javafx.scene.image.Image;
import javafx.scene.layout.HBox;

public class Exercise14_03 extends Application {
    @Override
    public void start(Stage primaryStage) {
        ArrayList<String> cards = new ArrayList<>();

        for (int i = 0; i < 52; i++) {
            cards.add(String.valueOf(i + 1));

            java.util.Collections.shuffle(cards);

            ImageView view1 = new ImageView(
                    new Image("https://liveexample.pearsoncmg.com/book/image/card/" + cards.get(0) + ".png"));
            ImageView view2 = new ImageView(
                    new Image("https://liveexample.pearsoncmg.com/book/image/card/" + cards.get(1) + ".png"));
            ImageView view3 = new ImageView(
                    new Image("https://liveexample.pearsoncmg.com/book/image/card/" + cards.get(2) + ".png"));

            HBox root = new HBox();

            root.getChildren().add(view1);
            root.getChildren().add(view2);
            root.getChildren().add(view3);

            Scene scene = new Scene(root);

            primaryStage.setTitle("Exercise14_03");
            primaryStage.setScene(scene);
            primaryStage.show();
        }
    }

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

现在问题很明显：几乎整个start(...)方法都在for循环中。在循环的第一次迭代中，添加第一个元素，然后尝试访问元素0,1和2，从而导致IndexOutOfBoundsException。

只需将代码移出for循环：

import java.util.ArrayList;
import javafx.application.Application;
import javafx.stage.Stage;
import javafx.scene.Scene;
import javafx.scene.image.ImageView;
import javafx.scene.image.Image;
import javafx.scene.layout.HBox;

public class Exercise14_03 extends Application {
    @Override
    public void start(Stage primaryStage) {
        ArrayList<String> cards = new ArrayList<>();

        for (int i = 0; i < 52; i++) {
            cards.add(String.valueOf(i + 1));
        }

        java.util.Collections.shuffle(cards);

        ImageView view1 = new ImageView(
                new Image("https://liveexample.pearsoncmg.com/book/image/card/" + cards.get(0) + ".png"));
        ImageView view2 = new ImageView(
                new Image("https://liveexample.pearsoncmg.com/book/image/card/" + cards.get(1) + ".png"));
        ImageView view3 = new ImageView(
                new Image("https://liveexample.pearsoncmg.com/book/image/card/" + cards.get(2) + ".png"));

        HBox root = new HBox();

        root.getChildren().add(view1);
        root.getChildren().add(view2);
        root.getChildren().add(view3);

        Scene scene = new Scene(root);

        primaryStage.setTitle("Exercise14_03");
        primaryStage.setScene(scene);
        primaryStage.show();
    }

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

学习how to read the stack trace也很有用。