Why is it preferred to declare: List list = new ArrayList(); instead of ArrayList = new ArrayList();

It is preferred because:

1. If later on code needs to be changed from ArrayList to Vector then only at the declaration place we can do that.
2. The most important one – If a function is declared such that it takes list. E.g void showDetails(List list);
   When the parameter is declared as List to the function it can be called by passing any subclass of List like ArrayList,Vector,LinkedList making the function more flexible