Java ConcurrentModificationException

exception, java

Solution

I'm seeing the same thing,

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class Launcher 
{
    public static void main(String[] args) 
    {
        doThis();
        doThat();
    }

    private static void doThis()
    {
        System.out.println("dothis");
        try
        {
            List<String> myList1 = new ArrayList<String>();
            Collections.addAll(myList1, "str1","str2","str3","str4","str5");
            for(String element : myList1){//no ConcurrentModificationException here
            if(element.equalsIgnoreCase("str4"))
                myList1.remove("str4");
            }
            System.out.println(myList1);
        }
        catch(Exception e)
        {
            e.printStackTrace();
        }
    }

    private static void doThat()
    {
        System.out.println("dothat");
        try
        {
            List<String> myList2 = new ArrayList<String>();
            Collections.addAll(myList2, "str1","str2","str3","str4","str5");
            for(String element : myList2){//ConcurrentModificationException here
            if(element.equalsIgnoreCase("str1"))
                myList2.remove("str1");
            }
            System.out.println(myList2);
        }
        catch(Exception e)
        {
            e.printStackTrace();
        }
    }
}

which outputs,

dothis
[str1, str2, str3, str5]
dothat
java.util.ConcurrentModificationException
    at java.util.AbstractList$Itr.checkForComodification(Unknown Source)
    at java.util.AbstractList$Itr.next(Unknown Source)
    at com.foo.Launcher.doThat(Launcher.java:41)
    at com.foo.Launcher.main(Launcher.java:12)

And I've found the reason.

Problem

when remove the second last element there is no ConcurrentModificationException ``` List<String> myList1 = new ArrayList<String>(); Collections.addAll(myList1, "str1","str2","str3","str4","str5"); for(String element : myList1){//no ConcurrentModificationException here if(element.equalsIgnoreCase("str4")) myList1.remove("str4"); } System.out.println(myList1); ``` But when remove other elements there is a ConcurrentModificationException ``` List<String> myList2 = new ArrayList<String>(); Collections.addAll(myList2, "str1","str2","str3","str4","str5"); for(String element : myList2){//ConcurrentModificationException here if(element.equalsIgnoreCase("str1")) myList2.remove("str1"); } System.out.println(myList2); ``` what is the reason?

Original source

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