| Sr. No. | Key | Fail-Fast | Fail-Safe |
|---|
1
| Exception
| Any changes in the collection, such as adding, removing and updating collection during a thread are iterating collection then Fail fast throw concurrent modification exception.
| The fail-safe collection doesn't throw exception.
|
2.
| Type of collection
| ArrayList and hashmap collection are the examples of fail-fast iterator
| CopyOnWrite and concurrent modification are the examples of a fail-safe iterator
|
3.
| Performance and Memory
| It's work on actual collection instead. So, this iterator doesn't require extra memory and time
| It's working on a clone of the collection instead of actual collection. It is overhead in terms of time and memory
|
4.
| Modifications
| Iterators don't allow modifications of a collection while iterating over it.
| Fail-Safe iterators allow modifications of a collection while iterating over it.
|
Example of FailSafe
public class FailSafeExample{
public static void main(String[] args){
ConcurrentHashMap<String, Integer> map = new ConcurrentHashMap<String, Integer>();
//Adding elements to map
map.put("Dell", 1);
map.put("IBM", 2);
//Getting an Iterator from map
Iterator<String> it = map.keySet().iterator();
while (it.hasNext()){
String key = (String) it.next();
System.out.println(key+" : "+map.get(key));
map.put("Google", 3);
}
}
}Output
IBM :2
Dell:1
Example of FailSafe
public class FailFastExample{
public static void main(String[] args){
List<Integer> list = new ArrayList<Integer>();
list.add(1);
list.add(2);
list.add(3);
//Getting an Iterator from list
Iterator<Integer> it = list.iterator();
while (it.hasNext()){
Integer integer = (Integer) it.next();
list.add(4);
}
}
}Output
Exception in thread "main" java.util.ConcurrentModificationException
at java.util.ArrayList$Itr.checkForComodification(Unknown Source)
