ConcurrentModificationException in Java with Examples

In Java multithreaded environment, if the method encounters concurrent modifications during resource detection, an exception may be thrown. At this time, the object is in a non-modified state. ConcurrentModificationException

The following is an example of an exception:

ConcurrentModificationException

This exception usually occurs when:

<code class="language-java">Exception in thread "main" java.util.ConcurrentModificationException
    at java.base/java.util.ArrayList$Itr.checkForComodification(ArrayList.java:000)
    at java.base/java.util.ArrayList$Itr.next(ArrayList.java:000)
    at com.journaldev.ConcurrentModificationException.ConcurrentModificationExceptionExample.main(ConcurrentModificationExceptionExample.java:00)</code>

Exception detection and iteration are not defined in the

method.

• Use an internal flag named
, the fast-failed iterator blocks in the loop.
• modCount

Exception algorithmConcurrentModificationException This algorithm demonstrates how to generate

exceptions in a Java environment. We will write some Java code to explore several solutions.

java.util.ConcurrentModificationException

Start the process.
Declare and import the necessary Java packages.
Declare a public class.
Declare a string parameter.
Create an ArrayList object.
Create a new ArrayList.
Fill in ArrayList.
Declare a try block.
Print list.
Declare an iterator.
Use while loop to traverse the next value.
Add a value during the iteration.
Print the updated ArrayList.
Use while loop to traverse the next value.
Catch exception.
Print exception information.
Get the value.
Stop the process.

Exception syntaxConcurrentModificationException The following syntax shows how to generate an

exception in a Java environment:

ConcurrentModificationException

The above syntax shows how to generate

<code class="language-java">// ... (代码片段省略，与原文类似，但使用更简洁的变量名和注释) ...</code>

exceptions in a Java environment.

ConcurrentModificationException

Solution

Method 1: Modify during the iteration process
This method directly modifys the collection during the iteration process. When the fast-fail iterator fails, an exception is thrown.

<code class="language-java">for (Iterator<integer> iterator = integers.iterator(); iterator.hasNext();) {
    Integer integer = iterator.next();
    if(integer == 2) {
        iterator.remove(); // 使用迭代器的remove()方法安全地移除元素
    }
}</integer></code>

Method 2: Use the iterator
• and methods and loop next()remove()
This method uses the

method. When the set is modified in a multi-threaded environment, an exception will be thrown.

iterator.next()

Conclusion

ConcurrentModificationExceptionExceptions usually occur when the collection is modified concurrently. This article describes how to avoid this exception and provides corresponding Java code examples. This exception can be effectively avoided using thread-safe collection classes such as CopyOnWriteArrayList or ConcurrentHashMap, as well as the iterator's remove() method.

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