how to create Synchronized arraylist

user_358471 0
Viewed 45425

i have created synchronized arrayList like this

import java.text.SimpleDateFormat;
import java.util.*;


class HelloThread  
{

 int i=1;
 List arrayList;
  public  void go()
  {
 arrayList=Collections.synchronizedList(new ArrayList());
 Thread thread1=new Thread(new Runnable() {

  public void run() {
  while(i<=10)
  {
   arrayList.add(i);
   i++;
  }
  }
 });
 thread1.start();
 Thread thred2=new Thread(new Runnable() {
  public void run() {
     while(true)
     {
   Iterator it=arrayList.iterator();
      while(it.hasNext())
      {
       System.out.println(it.next());
      }
     }
  }
 });
 thred2.start();
  }
 }

public class test
{
  public static void main(String[] args)
  {
   HelloThread hello=new HelloThread();
   hello.go();
  }
}

but getting exception like this

Exception in thread "Thread-1" java.util.ConcurrentModificationException

anything wrong in my approach ?

synchronization multithreading java
8 Answers

ArrayList is non-synchronized collection and should not be used in concurrent environment without explicit synchronization. To synchronize ArrayList, we can use two methods provided by JDK

  • Collections.synchronizedList() method – It returns synchronized list backed by the specified list. It is recommended that we should manually synchronize on the returned list when traversing it via Iterator, Spliterator or Stream. Else it may result in non-deterministic behavior. No explicit synchronization is needed to add, remove elements from synchronized arraylist
  • CopyOnWriteArrayList class – It is a thread-safe variant of ArrayList.

Since you are using iterator without explicit synchronization you are getting the error

user_39708950
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