对 java ConcurrentHashMap 中的值进行排序

发布于 2024-09-14 18:51:30 字数 570 浏览 3 评论 0原文

我有以下用于对 ConcurrentHashMap 进行排序的代码：

ConcurrentHashMap<String,String> text = new ConcurrentHashMap<String,String>();
.... 
List<String> list = new ArrayList<String>(text.values());
Collections.sort(list);

抛出 NoSuchElementException：

Caused by: java.util.NoSuchElementException
        at library.ArrayList$Itr.next(ArrayList.java:1232)
        at library.ArrayList$ListItr.next(ArrayList.java:1263)
        at java.util.Collections.sort(Collections.java:120)

我不知道为什么。有什么想法吗？

原文

I have the following code for sorting a ConcurrentHashMap:

ConcurrentHashMap<String,String> text = new ConcurrentHashMap<String,String>();
.... 
List<String> list = new ArrayList<String>(text.values());
Collections.sort(list);

Which throws a NoSuchElementException:

Caused by: java.util.NoSuchElementException
        at library.ArrayList$Itr.next(ArrayList.java:1232)
        at library.ArrayList$ListItr.next(ArrayList.java:1263)
        at java.util.Collections.sort(Collections.java:120)

And I can't work out why. Any ideas?

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人生百味 2024-09-21 18:51:30

根据 java api

NoSuchElementException
由 nextElement 方法抛出
枚举表明有
枚举中不再有元素。

我在本地测试了以下代码

ConcurrentHashMap<String, String> t = new ConcurrentHashMap<String, String>();

List<String> al = new ArrayList<String>(t.values());
Collections.sort(al);

System.out.println("no bugs");

（使用 Eclipse jdk 1.5），得到了预期的输出。在将一些键值对放入 ConcurrentHashMap 后，我还运行了本地测试，没有出现任何问题。根据我的成功，似乎以下一项（或两项）导致了我们的结果之间的差异。

A) 我们使用不同的类实现（我使用 jdk 1.5 中的 java.util.concurrent.ConcurrentHashMap、java.util.List、java.util.ArrayList）

B) 您正在修改 ArrayList 的内容或 ConcurrentHashMap ，而迭代器正在迭代所述对象的内容。运行排序时是否出现异常？我最好的猜测是，在您排序时，另一个线程正在干扰您的 ArrayList（因为 ConcurentHashMap 应该是线程安全的）。

According to the java api

NoSuchElementException
Thrown by the nextElement method of an
Enumeration to indicate that there are
no more elements in the enumeration.

I tested the following code locally

ConcurrentHashMap<String, String> t = new ConcurrentHashMap<String, String>();

List<String> al = new ArrayList<String>(t.values());
Collections.sort(al);

System.out.println("no bugs");

(with Eclipse jdk 1.5) I get the expected output. I also ran my local test after putting some key-value pairs into the ConcurrentHashMap and had no problems. Based on my successes, it would seem that one (or both) of the following is causing the discrepancy between our results.

A) We are using different class implementations (I use java.util.concurrent.ConcurrentHashMap, java.util.List, java.util.ArrayList from jdk 1.5)

B) You are modifying the contents of ArrayList or ConcurrentHashMap WHILE an iterator is iterating through the contents of said object. Does the exception occur while running the sort? My best guess is another thread is messing with your ArrayList (since ConcurentHashMap is supposed to be thread safe) while you are sorting.

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隱形的亼 2024-09-21 18:51:30

没有必要创建一个新的 ArrayList 来进行排序，因此，你可以这样做:

ConcurrentHashMap<String,String> text = new ConcurrentHashMap<String,String>();
List<String> textList=text.values(); //unmodifiable List here.
Collections.sort(textList);// it also can sort.

:EOF

It's unnessary to create a new ArrayList for sorting,thus,you can do like this :

ConcurrentHashMap<String,String> text = new ConcurrentHashMap<String,String>();
List<String> textList=text.values(); //unmodifiable List here.
Collections.sort(textList);// it also can sort.

:EOF

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