Question

I know this question has be asked before generic comes out. Array does win out a bit given Array enforces the return type, it’s more type-safe.

But now, with latest JDK 7, every time when I design this type of APIs:

public String[] getElements(String type)
vs
public List<String> getElements(String type)

I am always struggling to think of some good reasons to return A Collection over An Array or another way around. What’s the best practice when it comes to the case of choosing String[] or List as the API’s return type? Or it’s courses for horses.

I don’t have a special case in my mind, I am more looking for a generic pros/cons comparison.

Answer 1

Here is a partial list

Advantages of array:

• Fast
• Mutable by nature
• You know exactly “what you get” (what is the type) – so you know exactly how the returned object will behave.

Advantages of list:

• Behavior varies depending on actual type returned (for example – can be mutable or immutable depending on the actual type)
• Better hirerchy design
• (Depending on actual type) might be dynamic size
• More intuitive hashCode(), equals() – which might be critical if feeding to a hash based collection as a key.

• Type safety:

  String[] arr1 = new String[5]; 
  Object[] arr2 = arr1;
  arr2[0] = new Object(); //run time error :(
  List<String> list1 = new LinkedList<String>();
  List<Object> list2 = list1; //compilation error :)