Java 从stage和ArrayList中删除元素时的ConcurrentModification异常

我正在试验JavaFX动画。我在屏幕上的任意位置生成矩形，它们随着我定义的球移动。每当屏幕左侧出现矩形时，我都会将其从场景和包含它的ArrayList中删除。这是我的密码：

package UI;

import javafx.animation.AnimationTimer;
import javafx.fxml.FXML;
import javafx.scene.control.Label;
import javafx.scene.layout.AnchorPane;
import javafx.scene.shape.Circle;
import javafx.scene.shape.Rectangle;

import java.util.ArrayList;
import java.util.ConcurrentModificationException;
import java.util.Random;

public class UIController extends AnimationTimer {

@FXML
private Label fpsLbl;

@FXML
private Circle moveMeCircle;

@FXML
private AnchorPane root;

private ArrayList<Rectangle> rectangles = new ArrayList<>();

int fps = 0;

int deltaX = 5;
int deltaY = 0;

long start = 0;

@FXML
public void initialize() {
    super.start();
}

@Override
public void handle(long l) {
    if (start == 0) {
        start = l;
    } else {
        if (l >= start + 1000000000) {
            fpsLbl.setText("FPS: " + ((l - start) / 1000000000) * fps);
            System.out.println(fps);
            renderShape();
            if (fps < 59) {
                System.out.println(rectangles.size());
            }
            fps = 0;
            start = l;
        }
    }
    updateElements();
    fps++;
}

private void renderShape() {
    try{
    for (Rectangle rectangle : rectangles) {
        if (rectangle.getX()+rectangle.getWidth() < 0) {//this is the part 
            rectangles.remove(rectangle);               //that causes the
            root.getChildren().remove(rectangle);       //exception

        }
    }}
    catch(ConcurrentModificationException e){
        e.printStackTrace();
        }
    Random rand = new Random();
    int posX = rand.nextInt(1280);
    int posY = rand.nextInt(720);
    rectangles.add(new Rectangle(posX, posY, 100, 50));


    for (Rectangle rect : rectangles) {
        if (!root.getChildren().contains(rect)) {
            rect.setWidth(rand.nextInt(300 + 650));
            root.getChildren().add(rect);
        }
    }
}

private void updateElements() {
    if ((moveMeCircle.getCenterX() >= 1280 && deltaX > 0) || (moveMeCircle.getCenterX() <= 0 && deltaX < 0)) {
        deltaX = deltaX * -1;
    }
    if ((moveMeCircle.getCenterY() <= 0 && deltaY < 0) || (moveMeCircle.getCenterY() >= 720 && deltaY > 0)) {
        deltaY = deltaY * -1;
    }
    for (Rectangle rect : rectangles) {
        rect.setX(rect.getX() + deltaX);
        rect.setY(rect.getY() + deltaY);
    }
    moveMeCircle.setCenterX(moveMeCircle.getCenterX() + deltaX);
    moveMeCircle.setCenterY(moveMeCircle.getCenterY() + deltaY);
}
}

还有FXML文件，虽然它基本上是不相关的，但我只定义了锚烷和正在移动的球：

<?import javafx.scene.layout.AnchorPane?>
<?import javafx.scene.shape.Circle?>
<?import javafx.scene.shape.Rectangle?>
<?import javafx.scene.control.Label?>
<AnchorPane fx:id="root" maxHeight="-Infinity" maxWidth="-Infinity" 
minHeight="-Infinity" minWidth="-Infinity" prefHeight="720.0"
        prefWidth="1280.0" scaleShape="false" style="-fx-background-color: 
        #a4a4bd;"stylesheets="@css/main.css" 
        xmlns="http://javafx.com/javafx/10" 
        xmlns:fx="http://javafx.com/fxml/1"fx:controller="UI.UIController">
    <children>
        <Label fx:id="fpsLbl" prefWidth="200" AnchorPane.leftAnchor="0" 
        style="-fx-text-fill: blueviolet; -fx-font:20px 'Agency FB'"/>
        <Circle radius="10" centerX="50" centerY="50" fx:id="moveMeCircle"/>
    </children>
</AnchorPane>

与其他有关此异常和从ArrayList中删除的问题相同。使用迭代器来解决这个问题。有关详细信息，请参见类似问题的答案。@HovercraftFullOfEels那么是arraylist导致了这种情况？我假设这是因为我同时从arraylist和root的子元素中删除。谢谢如果您在遍历列表时从列表中删除，迭代器会变得混乱（它无法轻松跟踪哪个元素应该是“当前”元素）。@James_D Ah我明白了，所以我应该实现一个迭代器，而不是for:each？参见链接问题。。。

<?import javafx.scene.layout.AnchorPane?>
<?import javafx.scene.shape.Circle?>
<?import javafx.scene.shape.Rectangle?>
<?import javafx.scene.control.Label?>
<AnchorPane fx:id="root" maxHeight="-Infinity" maxWidth="-Infinity" 
minHeight="-Infinity" minWidth="-Infinity" prefHeight="720.0"
        prefWidth="1280.0" scaleShape="false" style="-fx-background-color: 
        #a4a4bd;"stylesheets="@css/main.css" 
        xmlns="http://javafx.com/javafx/10" 
        xmlns:fx="http://javafx.com/fxml/1"fx:controller="UI.UIController">
    <children>
        <Label fx:id="fpsLbl" prefWidth="200" AnchorPane.leftAnchor="0" 
        style="-fx-text-fill: blueviolet; -fx-font:20px 'Agency FB'"/>
        <Circle radius="10" centerX="50" centerY="50" fx:id="moveMeCircle"/>
    </children>
</AnchorPane>