java - 从 ArrayList 中删除对象时如何避免并发修改异常”

Question

考虑以下代码。

正如您所料，当在 for-each 循环内删除水果时，deleteFruitByName 方法会引发 ConcurrentModificationException。

在这种情况下我该如何避免这种情况？

import java.util.ArrayList;

public class Stringplay {
    public static void main(String[] args) {
        ArrayList<Fruit> fruites = new ArrayList<Fruit>();
        new Fruit(32, "apple", "red");
        new Fruit(64, "orange", "orange");
        new Fruit(12, "banana", "red");
        new Fruit(42, "grape", "purple");
        fruites.addAll(Fruit.fruits);
        Fruit.deleteFruitByName("apple");
        for (Fruit fruit : fruites) {
            System.out.println(fruit.getName());
        }
    }

}

public class Fruit {
    public int weight;
    public String name;
    public String type;
    public static ArrayList<Fruit> fruits = new ArrayList<Fruit>();

    public Fruit(int weight, String name, String type) {
        this.weight = weight;
        this.name = name;
        this.type = type;
        fruits.add(this);
    }

    public String getName() {
        return name;
    }

    public static void deleteFruitByName(String fruitName) {
        for (Fruit fruit : fruits) {
            if (fruit.getName().equals(fruitName)) {
                fruits.remove(fruit);
            }
        }

    }
}

Answer 1

为了避免 ConcurrentModificationException，您需要在此处使用 Iterator。

    public static void deleteFruitByName(String fruitName) {
        Iterator<Fruit> it = fruits.iterator();
        while (it.hasNext()) {
            Fruit fruit = it.next();
            if (fruit.getName().equals(fruitName)) {
                it.remove();
            }
        }
    }

来自java doc

The iterators returned by this class's iterator and listIterator methods are fail-fast: if the list is structurally modified at any time after the iterator is created, in any way except through the iterator's own remove or add methods, the iterator will throw a ConcurrentModificationException. Thus, in the face of concurrent modification, the iterator fails quickly and cleanly, rather than risking arbitrary, non-deterministic behavior at an undetermined time in the future.

更新:要迭代 Fluit 类中的集合，请使用此代码

public class Main {

    public static void main(String[] args) {
        new Fruit(32, "apple", "red");
        new Fruit(64, "orange", "orange");
        new Fruit(12, "banana", "red");
        new Fruit(42, "grape", "purple");
        Fruit.deleteFruitByName("apple");
        for (Fruit fruit : Fruit.fruits) {
            System.out.println(fruit.getName());
        }
    }
}