Collections.emptyList() instead of null check?

Question

If I have a rarely used collection in some class which may be instantiated many times, I may sometimes resort to the following \"idiom\" in order to save unnecessary object crea

Answer 1

Here's a variation on using optional as @Stas suggested, but also using the isEmpty immutable collection as originally requested in the question:

public static List<String> addElement(List<String> list, String toAdd) {
   List<String> newList = Optional.ofNullable(list).orElse(Collections.emptyList());
   newList.add(toAdd);
   return newList;
}

This approach is also the closest thing I can find to the nice ability in Javascript to use an empty array if the collection is null.

For example:

// no need to indent everything inside a null check of myObjects
for (MyObj myObj : Optional.ofNullable(myObjects).orElse(Collections.emptyList())){
    // do stuff with myObj
}

Answer 2

If you only use the list for iterations, you could just use: for (Object object : list) which wouldn't do anything for empty lists, i.e. not a single iteration.

Otherwise just check list.isEmpty().

Answer 3

There is an emptyIfNull method in package org.apache.commons.collections4;. It returns an empty list if the one provided is null.

List<Object> list = CollectionUtils.emptyIfNull(list);