Re: Object creation overhead
From: nos (nos_at_nospam.com)
Date: 11/27/03
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Date: Thu, 27 Nov 2003 05:23:19 GMT
ya, very helpful, thanks for taking the time to explain
"Anthony Borla" <ajborla@bigpond.com> wrote in message
news:x0cxb.28557$aT.9305@news-server.bigpond.net.au...
>
> "nos" <nos@nospam.com> wrote in message
> news:shbxb.316149$Tr4.986273@attbi_s03...
> >
> > please, what is a "proxy" object? how to make one?
> >
>
> It's just a plain object that is used to represent or take the place of
> another object. While useful in many situations [i.e. there can be many
> reasons for using proxies including security reasons, and minimising
> resources loadtimes etc], one particular use is to reduce the memory
> footprint of a Collection-type of data structure.
>
> For example, you need to have an 'ArrayList' object manage 1000 objects of
> 'MyClass'; this class looks like:
>
> class MyClass
> {
> ...
> // Lots of fields ...
> private long id;
> private String name;
> private String address;
> ...
> }
>
> If 'MyClass' has twenty 'String' fields then that means that memory for
> 20,000 'String' objects is needed, both to manage them, and for the
'String'
> data. This is, of course, over and above the memory required for the
> 'MyClass' objects themselves.
>
> The 'proxy' class approach won't see a reduction in the number of
'MyClass'
> objects, merely a reduction in the amount of memory each may require for
its
> field data. So, the original class is now split into two; there is the
proxy
> class:
>
> class MyClassProxy
> {
> ...
> // Only a couple of fields needed...
> private long id;
> ...
> // Method to retrieve the actual object proxied by this one
> public MyClass getMyClassObject() { ... }
> ...
> }
>
> and a modified, probably pared-down, version of the original class:
>
> class MyClass
> {
> ...
> // Still lots of fields, but probably less methods ...
> private long id;
> private String name;
> private String address;
> ...
> }
>
> With the 'ArrayList' object loaded with 'MyClassProxy' objects, less
memory
> is being used. Only when a 'MyClassProxy' object is selected is a
'MyClass'
> object instantiated, using data stored somewhere else *outside memory*
[e.g.
> file, database, URL, etc].
>
> Note:
>
> * This approach has many variants - I have provided a very simple
> example, and ignored / glossed over the implementation issues.
> However the general approach is:
>
> - Use proxy object in place of real object
>
> - When proxy object is selected have it retrieve / create
> the real object
>
> * Proxy cannot [usually] be used where access / retrieval time is
> crucial
>
> More substantial examples, and relevant in-depth discussions may be found
by
> Google searching for 'Proxy Design Pattern'.
>
> I hope this helps.
>
> Anthony Borla
>
>
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