当从ArrayLists中删除对象时如何避免并发ModificationException“

Question

请考虑以下代码。如您所料，它将引发ConcurrentModificationException。在这种情况下如何避免这种情况？................................................... ...................................................

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());
        }
    }

}


import java.util.ArrayList;

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 int getWeight() {
        return weight;
    }

    public String getName() {
        return name;
    }

    public String getType() {
        return type;
    }

    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

由此类的迭代器和listIterator方法返回的迭代器是快速失败的：如果在创建迭代器后的任何时候以任何方式对列表进行结构修改，除非通过迭代器自己的remove或add方法，否则迭代器都会抛出一个ConcurrentModificationException。因此，面对并发修改，迭代器会快速干净地失败，而不会在未来的不确定时间内冒任意，不确定的行为的风险。

更新：要在Fluit类中迭代集合，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());
        }
    }
}