J.U.C——CopyOnWriteArrayList

ArrayList 遍历无法修改值

public class CopyOnWriteArrayListTest {
    public static void main(String[] args) {
        ArrayList<String>list = new ArrayList<>();
        list.add("1");
        list.add("2");
        list.add("3");
        list.add("4");
        list.add("5");
        Iterator<String> iterator = list.iterator();
        while (iterator.hasNext()) {
            System.out.println("list is" + list);
            String next = iterator.next();
            System.out.println(next);
            if (next.equals("2")) {
                list.remove("5");
            }
            if (next.equals("3")) {
                list.add("3 found");
            }
        }
    }
}

执行结果异常

list is[1, 2, 3, 4, 5]
1
list is[1, 2, 3, 4, 5]
2
list is[1, 2, 3, 4]
Exception in thread "main" java.util.ConcurrentModificationException
    at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:911)
    at java.util.ArrayList$Itr.next(ArrayList.java:861)
    at com.example.concurrent.collections.CopyOnWriteArrayListTest.main(CopyOnWriteArrayListTest.java:25)

替换成CopyOnWriteArrayList

public class CopyOnWriteArrayListTest {
    public static void main(String[] args) {
        //ArrayList<String>list = new ArrayList<>();
        CopyOnWriteArrayList<String> list = new CopyOnWriteArrayList();
        list.add("1");
        list.add("2");
        list.add("3");
        list.add("4");
        list.add("5");
        Iterator<String> iterator = list.iterator();
        while (iterator.hasNext()) {
            System.out.println("list is" + list);
            String next = iterator.next();
            System.out.println(next);
            if (next.equals("2")) {
                list.remove("5");
            }
            if (next.equals("3")) {
                list.add("3 found");
            }
        }
    }
}