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Difference between fail-fast and fail safe in Java
| 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)
Updated on: 18-Nov-2019
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