Yes object creation is expensive but so are a lot of things. Using instanceof and reflection is expensive too but that doesn't stop people from using it.
My theory on performance issues like this is that you should be aware when something is a little more expensive than average (like object creation, string concatenation, etc.) and try to cut down on that if possible. The thing about it is that most of the time your efforts to "optimize" your code will result in unecessary complexity without any real benefit. You shouldn't ignore performance issues but IMO too many programmers put too much emphasis on them. Ask yourself, are you writing the next Amazon.com or is this just a typical web application that has a few hundred users? Will the user really notice the difference between 110 ms and 108ms? Code that does exactly what you want and is easy to maintain. That should always be your goal. Don't ignore performance issues but don't let them stop you from doing what you want to do. sean On Fri, 11 Feb 2005 14:18:49 +0100, Matthias Wessendorf <[EMAIL PROTECTED]> wrote: > Sean, > > thanks for your replay > > Sean Schofield wrote: > > Matthias, > > > > Its true that object creation can be expensive but you also have to > > consider how often the underlying data (assuming it comes from a > > database) changes. In Struts you have ActionForms which are > > essentially request scope beans (similar to but not the same as > > backing beans). Its no big deal constantly creating these every > > sure not similar, since backing beans has more *features* > as only being a "form-bean". Btw. scope attribute's value > of <action/> is "session" as default. > > > request. > > > > You also want to consider that session beans take up server memory. > > If you have ten different backing beans for ten different pages you > > will have ten beans sitting around in memory for each user that goes > > through those ten pages (until the session expires.) > > ah, yes good point! thanks. > > > In my application we are going to have to use a lot of request scope > > beans beacause the data needs to be up to date. It can be changed by > > That is also the thing that I wanted to do! But my co-worker said: > "make them to session, sicne creation is VERY expensive" > > --> reason for my mail > > > other users at any time, so we want to show the latest on every > > request. In theory you could have a session bean to avoid recreating > > the object and use a scheme to repopulate it but I am not wild about > > that. > > Ok, thanks! > > I remember that Craig also allways mentioned request instead of session, > but couldn't find a thread on that... > > -Matthias > > > Anyways that is my .02, > > > > sean > > > > > > On Fri, 11 Feb 2005 11:35:16 +0100, Matthias Wessendorf > > <[EMAIL PROTECTED]> wrote: > > > >>Hi all, > >> > >>I am just on reading [1]. There is mentioned, that > >>object creation is very expensive and you should better > >>reuse objects instead of creating them often. > >> > >>Now I thought about scope of my backing beans. > >>What should be better request or session? > >> > >>If I have request scoped backing beans that > >>get often created by ONE user and I have MANY > >>users... will request scope slow down my web app? > >> > >>Ok... application is also there, but that is > >>an other stage :-) I would use such a backing > >>bean only for *knowing* about ALL users logged > >>into the application. > >> > >>[1] http://www.oreilly.com/catalog/javapt/chapter/ch04.html > >> > >> > >>-Matthias > >> > > > > > > -- > Matthias We�endorf > Aechterhoek 18 > DE-48282 Emsdetten > Germany > phone: +49-2572-9170275 > cell phone: +49-179-1118979 > email: matzew AT apache DOT org > url: http://www.wessendorf.net > callto://mwessendorf (Skype) > icq: 47016183 > > -- > Matthias We�endorf > Aechterhoek 18 > DE-48282 Emsdetten > Germany > phone: +49-2572-9170275 > cell phone: +49-179-1118979 > email: matzew AT apache DOT org > url: http://www.wessendorf.net > callto://mwessendorf (Skype) > icq: 47016183 >
