blocks|key|114626|text|请注意，如果您使用迭代器，Collections.synchronizedMap永远不会保护您免受并发修改。此外，除非您从多个线程访问Map，否则创建同步映射是无用的。没有传递给其他线程的局部作用域集合和变量不需要是+synchronized**.**|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|BOLD|entityRanges|data|114627|我的猜测是，在您省略的代码中，您正在迭代Map.entrySet、Map.keySet或Map.values之一，并在此迭代期间调用put+(在for循环中)。使用您所展示的代码，这是唯一可能实现的方法。|114628|entityMap^0|D|R|1V|3|31|C|2M|E|31|E|0|K|C|X|A|18|A|1U|3|20|3|0^^$0|@$1|2|3|4|5|6|7|K|8|@$9|L|A|M|B|C]|$9|N|A|O|B|C]|$9|P|A|Q|B|C]|$9|R|A|S|B|D]|$9|T|A|U|B|D]]|E|@]|F|$]]|$1|G|3|H|5|6|7|V|8|@$9|W|A|X|B|C]|$9|Y|A|Z|B|C]|$9|10|A|11|B|C]|$9|12|A|13|B|C]|$9|14|A|15|B|C]]|E|@]|F|$]]|$1|I|3|-4|5|6|7|16|8|@]|E|@]|F|$]]]|J|$]]

Note that <code>Collections.synchronizedMap</code> will never protect you from concurrent modification if you're using an iterator. In addition, unless you're accessing your <code>Map</code> from more than one thread, creating the synchronized map is useless. Locally-scoped collections and variables that are not being handed to other threads do not need to be <code>synchronized</code>.

My guess is that in the code you left out, you're iterating over one of <code>Map.entrySet</code>, <code>Map.keySet</code>, or <code>Map.values</code>, and calling <code>put</code> during that iteration (within the <code>for</code> loop). With the code you've shown, this is the only way this could happen.

blocks|key|700910|text|您似乎正在获取已同步映射的同步映射。如果我将对function1()的调用替换为it's+contents+(simplified)，我们得到：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|700911|Map<String,+String>+key_values+=Collections.synchronizedMap(Collections.synchronizedMap(+new+TreeMap<String,+String>()));|code-block|syntax|javascript|700912|我认为你的呼叫线应该改为：|700913|Map<String,+String>+key_values+=+Classname.function1();|700914|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

You appear to be getting a synchronized map of a synchronized map. If I replace the call to function1() with a it's contents (simplified) we have:

<pre><code>Map&lt;String, String&gt; key_values =Collections.synchronizedMap(Collections.synchronizedMap( new TreeMap&lt;String, String&gt;()));
</code></pre>

I think your calling line should be changed to:

<pre><code>Map&lt;String, String&gt; key_values = Classname.function1();
</code></pre>

blocks|key|4532774|text|您正在寻找一个同步的地图，所以我假设您正在处理一个多线程应用程序。在这种情况下，如果您想要使用迭代器，则必须为MAP设置同步块。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4532775|/*This+reference+will+give+error+if+you+update+the+map+after+synchronizing+values.*/
++++Map<String,+String>+values+=Collections.synchronizedMap(function1());

/*This+reference+will+not+give+error+if+you+update+the+map+after+synchronizing+values++*/
++++++++Map<String,+String>+values+=+Collections.synchronizedMap(new+TreeMap<String,+String>());


+++++synchronized+(values)+
++++++++++++++++{+++++++++++
++++++++++++++++++++Iterator+it+=+values.entrySet().iterator();
++++++++++++++++++++while(it.hasNext())
++++++++++++++++++++{
++++++++++++++++++++++++it.next()+;+
++++//+You+can+update+the+map+here.+++++
++++++++++++++++++++}
++++++++++++++++}|code-block|syntax|javascript|4532776|更新：|4532777|实际上，在您的例子中，考虑到您两次包装映射的错误，即使使用synchronized块在while循环中修改它，也会给出CM异常，因为您将无法在正在更新的原始映射对象上进行同步。|4532778|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

You are looking for a synchronized MAP, so I assume you are dealing with a multithreaded app. In that case if you want to use iterator, you must synchronized block for the MAP.

<pre><code>/*This reference will give error if you update the map after synchronizing values.*/
 Map&lt;String, String&gt; values =Collections.synchronizedMap(function1());

/*This reference will not give error if you update the map after synchronizing values */
 Map&lt;String, String&gt; values = Collections.synchronizedMap(new TreeMap&lt;String, String&gt;());


 synchronized (values) 
 { 
 Iterator it = values.entrySet().iterator();
 while(it.hasNext())
 {
 it.next() ; 
 // You can update the map here. 
 }
 }
</code></pre>

Update :

Actually in your case, considering the err that you are twice wrapping the MAP, modifying it in the while loop even with a synchronized block will give a CM Exception as you would not be able to synchronize on the original MAP object that is getting udpated.

blocks|key|4532827|text|如果你使用ConcurrentSkipListMap，速度会更快，不会有这个问题。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|4532828|public+NavigableMap<String,+String>+function1()+{
++++NavigableMap<String,+String>+key_values+=+new+ConcurrentSkipListMap<String,+String>();
++++//+all+key_values.put()+goes+here

++++return+key_values;
}|code-block|syntax|javascript|4532829|如果不需要对键进行排序，可以使用ConcurrentHashMap。|4532830|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/ConcurrentSkipListMap.html|1|http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/ConcurrentHashMap.html^0|5|L|0|0|0|G|H|1|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@$A|V|B|W|1|X]]|C|$]]|$1|D|3|E|5|F|7|Y|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|Z|8|@]|9|@$A|10|B|11|1|12]]|C|$]]|$1|K|3|-4|5|6|7|13|8|@]|9|@]|C|$]]]|L|$M|$5|N|O|P|C|$Q|R]]|S|$5|N|O|P|C|$Q|T]]]]

If you use a <a href="http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/ConcurrentSkipListMap.html" rel="noreferrer">ConcurrentSkipListMap</a> is can be faster and doesn't have this issue.

<pre><code>public NavigableMap&lt;String, String&gt; function1() {
 NavigableMap&lt;String, String&gt; key_values = new ConcurrentSkipListMap&lt;String, String&gt;();
 // all key_values.put() goes here

 return key_values;
}
</code></pre>

If you don't need the keys to be sorted you can use a <a href="http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/ConcurrentHashMap.html" rel="noreferrer">ConcurrentHashMap</a>.

blocks|key|701053|text|我就是这么做的，引发了ConcurrentModificationException|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|701054|TreeMap<Integer,+Integer>+map+=+new+TreeMap<>();

for+(Integer+i+:+map.keySet())+{
++++map.remove(i)
}|code-block|syntax|javascript|701055|这是我对相同的功能所做的，以修复异常：|701056|TreeMap<Integer,+Integer>+map+=+new+TreeMap<>();

//+I+would+not+recommend+this+in+production+as+it+will+create+multiple
//+copies+of+map
for+(Integer+i+:+new+HashMap<>(integers).keySet())+{
++++map.remove(i)
}|701057|entityMap^0|B|V|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|T|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|U|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|V|8|@]|D|@]|E|$I|J]]|$1|O|3|-4|5|6|7|W|8|@]|D|@]|E|$]]]|P|$]]

This is what I was doing that raised <code>ConcurrentModificationException</code>:

<pre><code>TreeMap&lt;Integer, Integer&gt; map = new TreeMap&lt;&gt;();

for (Integer i : map.keySet()) {
 map.remove(i)
}
</code></pre>

This is what I did for the same functionality to fix the exception:

<pre><code>TreeMap&lt;Integer, Integer&gt; map = new TreeMap&lt;&gt;();

// I would not recommend this in production as it will create multiple
// copies of map
for (Integer i : new HashMap&lt;&gt;(integers).keySet()) {
 map.remove(i)
}
</code></pre>

I am calling function that returns <code>TreeMap</code> instance, and in the calling code I wanted to modify the <code>TreeMap</code>. However, I am getting a <code>ConcurrentModificationException</code>.

Here is my code:

<pre><code>public Map&lt;String, String&gt; function1() {
 Map&lt;String, String&gt; key_values = Collections.synchronizedMap(new TreeMap&lt;String, String&gt;());
 // all key_values.put() goes here

 return key_values;
}
</code></pre>

And my calling code is:

<pre><code>Map&lt;String, String&gt; key_values =Collections.synchronizedMap(Classname.function1());
//here key_values.put() giving ConcurrentModificationException
</code></pre>

Avoiding TreeMap ConcurrentModificationException?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我正在调用返回TreeMap实例的函数，并且在调用代码中我想修改TreeMap。然而，我得到了一个ConcurrentModificationException。下面是我的代码：public Map<String, String> function1() { Map<String, String> key_val...

问避免TreeMap ConcurrentModificationException？
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问避免TreeMap ConcurrentModificationException？EN