If you don't clone in Java then what do you do and what do you call it?

Question

Does anyone have any suggested or established best practices and naming conventions for copy constructors / factory methods etc in Java? In particular, say I have a class Thing and I want a method somewhere that returns a new Thing with the same value as a Thing passed in (or as the instance if it's an instance method). Would you have this as constructor or a static factory method or instance method? What would you call it?

As per the title, I want to avoid clone() and Cloneable.

Answer 1

Effective Java recommends either of the following:

1. A copy constructor (as noted by others):

   public Item(Item item)

2. A copy factory method:

   public static Item newInstance(Item item)

(Also, no copying for immutables)

The primary difference is that with #1 you choose the actual class of the result, and with #2 the implementer can return a subclass. The semantics of the class may guide you into which one is best.

Answer 2

I would call it a copy method or a copy constructor (as the case may be). If it was a static method, then I would call it a factory.

In terms of what to do, the most flexible and long living option is a copy constructor. This gives subclasses the ability to copy themselves just like the parent.