添加另一个对象时java.util.ConcurrentModificationException [英] java.util.ConcurrentModificationException when adding another object

问题描述

我正在遭遇这个例外。我的代码有什么问题？
我只想在另一个 ArrayList中分离Person的重复名称

I'm suffering on this exception. What's the problem on my code? I just want to separate Person's duplicate name in another ArrayList

public class GlennTestMain
{

    static ArrayList<Person> ps;

    static ArrayList<Person> duplicates;
    public static void main(String[] args)
    {
        ps = new ArrayList<GlennTestMain.Person>();

        duplicates = new ArrayList<GlennTestMain.Person>();

        noDuplicate(new Person("Glenn", 123));
        noDuplicate(new Person("Glenn", 423));
        noDuplicate(new Person("Joe", 1423)); // error here


        System.out.println(ps.size());
        System.out.println(duplicates.size());
    }

    public static void noDuplicate(Person p1)
    {
        if(ps.size() != 0)
        {
            for(Person p : ps)
            {
                if(p.name.equals(p1.name))
                {
                    duplicates.add(p1);
                }
                else
                {
                    ps.add(p1);
                }
            }
        }
        else
        {
            ps.add(p1);
        }
    }

    static class Person
    {
        public Person(String n, int num)
        {
            this.name = n;
            this.age = num;
        }
        String name;
        int age;
    }



}

这是堆栈跟踪

Exception in thread "main" java.util.ConcurrentModificationException
at java.util.ArrayList$Itr.checkForComodification(Unknown Source)
at java.util.ArrayList$Itr.next(Unknown Source)
at hk.com.GlennTestMain.noDuplicate(GlennTestMain.java:41)
at hk.com.GlennTestMain.main(GlennTestMain.java:30)

推荐答案

您无法修改正在迭代的集合。这可能会抛出 ConcurrentModificationException 。虽然它有时会起作用，但并不能保证每次都能正常工作。

You cannot modify the collection you are iterating on. That might throw a ConcurrentModificationException. Though it might work sometimes, but it is not guaranteed to work everytime.

如果要添加或删除列表中的内容，则需要使用 Iterator 或 ListIterator 列表。并使用 ListIterator #add 方法在列表中添加任何内容。即使在你的迭代器中，如果你试图使用 List.add 或 List.remove ，您将获得该异常，因为这没有任何区别。您应该使用 iterator 的方法。

If you want to add, or remove something from your list, you need to use an Iterator, or ListIterator for your list. And use ListIterator#add method to add anything in your list. Even if in your iterator, if you try to use List.add or List.remove, you will get that exception, because that doesn't make any difference. You should use the methods of iterator.

请参阅这些帖子以了解如何使用它： -

See these posts to understand how to use it: -

• Java ：迭代列表时出现ConcurrentModificationException


• 迭代集合，在循环中删除时避免ConcurrentModificationException

• Java : ConcurrentModificationException while iterating over list
• Iterating through a Collection, avoiding ConcurrentModificationException when removing in loop

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