From Effective Java 2/e by Joshua Bloch
There is no reason ever to return null from an array- or collection-valued method instead of returning an empty array or collection
// The right way to return an array from a collection
private final List<Cheese> cheesesInStock = ...;
private static final Cheese[] EMPTY_CHEESE_ARRAY = new Cheese[0];
/**
* @return an array containing all of the cheeses in the shop.
*/
public Cheese[] getCheeses() {
return cheesesInStock.toArray(EMPTY_CHEESE_ARRAY);
}
// The right way to return a copy of a collection
public List<Cheese> getCheeseList() {
if (cheesesInStock.isEmpty())
return Collections.emptyList(); // Always returns same list
else
return new ArrayList<Cheese>(cheesesInStock);
}
Returing null
- Doing so requires extra code in the client to handle the null return value
- It is error-prone, because the programmer writing the client might forget to write the special- case code to handle a null return
- Returning null in place of an empty array also complicates the method that returns the array or collection