Question

considering i have a method which gets a List passed as an param. Within this method i want to use for instance an ArrayList specific function on that list (lets say trimToSize()). What would be the general approach to deal with a problem like this ?
Here two example:

First approach (i don’t think this is good)

private void doSomething(final List<T> list) {
  // ... do something
  ((ArrayList<T>) list).trimToSize();
  // ... do something
}

Second approach (i think this one is better)

private void doSomething2(final List<T> list) {
final List<T> myList = new ArrayList<T>();
// Collections.copy(myList, list); or
myList.addAll(list);
((ArrayList<T>) myList).trimToSize();
//..do something
}

I’m curious whats the best solution for a problem like this.

Answer 1

Well, the preferred option is to just write the method to take an ArrayList in the first place. If you need ArrayList specific functionality, the method has no business taking a List. Transfer the responsibility of ensuring that the parameter is of the right type to the caller and don’t fiddle around with it inside the method.