Java : Exception in thread "main" java.util.ConcurrentModificationException
When Exception in thread "main" java.util.ConcurrentModificationException occurs.
package com.ekiras.demo; import java.util.ArrayList; import java.util.List; public class Test { public static void main(String args[]){ // create a new list List<String> list = new ArrayList<String>(); // add 50 items to the list for(int itr=0;itr<50;itr++) list.add("user-"+(itr+1)); // try to remove item from list while iterating the list for(String str : list){ if(str.equals("user-15")){ list.remove(str); } } } }
The above code will give the following error.
Exception in thread "main" java.util.ConcurrentModificationException at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:859) at java.util.ArrayList$Itr.next(ArrayList.java:831) at testing.Test.main(Test.java:18)
How to avoid ConcurrentModificationException
- Create the list of type CopyOnWriteArrayList, this will create a new copy of list for every operation performed and then replace it with original.
List<String> list = new CopyOnWriteArrayList<String>();
- Create a new copy of the list for iterating the list
for(String str : new ArrayList<String>(list))
- Use the Iterator to iterate the list and modify its contents.
Iterator<String> iterator = list.iterator(); while(iterator.hasNext()){ String str = iterator.next(); if(str.equals("user-15")){ iterator.remove(); } }
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