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[英]How to avoid a ConcurrentModificationException when removing objects from an ArrayList
[英]how to avoid concurrentModificationException when removing an object from to ArrayLists"
考虑以下代码。
如您所料,当在 for-each 循环中移除水果时,deleteFruitByName 方法会抛出 ConcurrentModificationException。
在这种情况下,我如何避免这种情况?
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);
}
}
}
}
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 文档
此类的 iterator 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间对列表进行结构修改,除了通过迭代器自己的 remove 或 add 方法,迭代器将抛出 ConcurrentModificationException。 因此,面对并发修改,迭代器快速而干净地失败,而不是在未来不确定的时间冒着任意、非确定性行为的风险。
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());
}
}
}
以下应该工作(只是在这里写,所以可能是一个编译错误):
public static void deleteFruitByName(StringfruitName) {fruit.removeIf(fruit =>fruit.getName().equals(fruitName)); }
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