Fail Safe and Fail Fast

Fail Fast: When we try to attempt concurrent modification or structural modification, It will not allow that to happen rather it will leave to exception. 

Eg: In case of for loop when we are adding the data while we are accessing then it will result in never ending loop. 

for (int i=0; i<al.size();i++)

{

System.out.println(al.get(i));

al.add(99)//

}

To overcome this we will use Iterator. If we use Iterator instead of for loop It will result in Fail Fast by giving exception.

Iterator itr=al.iterator();

while(itr.hasNext()){

system.out.println(itr.hasNext());

}

Fail Safe: It is a mechanism which will stop concurrent modification or structural modification without giving any exception.

U need to use CopyOnWriteArrayList class to achieve this

So, we will import the concurrent packages when we want to achieve Fail Safe