how to create Synchronized arraylist

Question

i have created synchronized arrayList like this

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


class HelloThread  
{

 int i=1;
 List arrayList;
           


        

Answer 1

Iterator of synchronizedList is not (and can't be) synchronized, you need to synchronize on the list manually while iterating (see javadoc):

synchronized(arrayList) {
    Iterator it=arrayList.iterator(); 
    while(it.hasNext()) { 
        System.out.println(it.next()); 
   } 
}

Another approach is to use a CopyOnWriteArrayList instead of Collections.synchronizedList(). It implements a copy-on-write semantic and therefore doesn't require synchronization.