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From: Martin Gregorie <martin@address-in-sig.invalid>
Newsgroups: comp.lang.java.programmer
Subject: Re: refactoring problem
Date: Sun, 3 Feb 2013 16:23:03 +0000 (UTC)
Organization: UK Free Software Network
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On Sun, 03 Feb 2013 06:30:40 -0800, Roedy Green wrote:

> Consider the following refactoring problem.
> 
> There is a hunk of almost identical code that appears multiple times.
> It sets up 6 local variables.
> 
> I would like to encapsulate it.
> 
>
> I could create a separate class just to hold the values.  This is
> tedious, but it may be the only way.
>
...which you can return from a method. I keep wondering whether I should 
use this approach but so far haven't used it.
 
> I think, why can methods have multiple inputs, but only one output? I
> have been thinking that for about 50 years, and it ,seems unlikely to
> change soon.
> 
Formally true, but not necessarily so in practice. You can return a class 
instance containing as many variables as you need to return.

You can also pass the constructor a reference to a mutable object which 
contains the variables you want to change. I use this quite a lot: its 
particularly useful for letting logically separate sets of methods access 
and manipulate a collection: each set of methods forms a class that's 
handed a reference to the collection.

Example: I've just finished dealing with a way of handling a collection 
of geographical points: Each point forms a Waypoint that contains 
coordinates and descriptive attributes together with the methods needed 
to access its (immutable) attributes. The collection forms a WaypointList 
class that holds a set of Waypoints as an ArrayList plus two TreeMaps 
that give keyed access to Waypoints and methods needed to add, remove and 
retrieve individual Waypoints. There is a requirement to read a waypoint 
file into the WaypointList and to write it out to a file: there are 
currently five externally defined waypoint file formats I need to deal 
with so there is a set of classes, one per file format, that each 
implement a load() and a save() method. 

In addition there will be three programs that carry out more complex 
operations on one or more WaypointLists: only one of these has been 
written so far.



-- 
martin@   | Martin Gregorie
gregorie. | Essex, UK
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