Getting the next CustomerID during instancing object
hi,
for a customer class i use an internal id(whcih gets generated by sql) and a customer is, which is a mixture of numbers and chars.
When i instanciate a new customer i want to automaticly lookup the last CustomerID and add 1. The question is where i would do this?
I tried it in the constructor like this:
public Customer(String _name, String _surname, String _address1, String _address2, String _postalCode, String _city, String _country, String _email, String _phone, Date _registered){
NextIds nextIds=null;
this._customerId = nextIds.getNextCustomerId();
this._name = _name;
this._surname = _surname;
this._address1 = _address1;
this._address2 = _address2;
this._postalCode = _postalCode;
this._city = _city;
this._country = _country;
this._email = _email;
this._phone = _phone;
this._registered = _registered;
}
wherby NextIds is:
publicabstractclass NextIds{
@InjectObject("service:com.nuromobile.accounting.hibernate.CustomerService")
publicabstract CustomerService getCustomerService();
publiclong getNextCustomerId(){
//loading id from the database, here it is 2000 as a test value
return 2000;
}
}
My error is:
java.lang.NullPointerException
How can i call functionality in the constructor to get the next CustomerID? Is it the right way to do it in the constructor?
Any advice is welcome.
[2046 byte] By [
Fabb81a] at [2007-10-3 9:12:41]
No wonder you get a null pointer exception. you set the variable nextIds to null and then you try to call a method from that null reference. What did you expect to get?
Masijade - did you read the title of this forum? Try helping people instead of making sarcy comments - it makes you look less like you are scared of someone else taking your job (assuming you have one)
Fabb, what Masijade would have said if he was a serious programmer is - you need to instantiate nextIDs before you can call the method getNextCustomerID() on it. It probably took him 2 hours to work that out, so forgive him for trying to sound superior.
However, if he had actually had any real knowledge, he would have suggested that you use a static variable on your Customer class, which would be ideal for what you are trying to do... like this
public class Customer {
private static int nextID = 1;
private int customerID;
public Customer() {
customerID = nextID++;
System.out.println("my id:" + customerID);
}
}
> Masijade - did you read the title of this forum? Try
> helping people instead of making sarcy comments - it
> makes you look less like you are scared of someone
> else taking your job (assuming you have one)
Where did you ride in from? I have no problems with anyone attempting to take my job. You are more than welcome to try. Also, I have no problems with newbies, but a little common sense is at least sometimes called for. when doing var = null and then var.whatever, it does not take a rocket scientist to then figure out why a NullPointerException was thrown.
> Fabb, what Masijade would have said if he was a
> serious programmer is - you need to instantiate
> nextIDs before you can call the method
> getNextCustomerID() on it. It probably took him 2
> hours to work that out, so forgive him for trying to
> sound superior.
And yes, he should instantiate it. And if you think is takes two hours you have a problem.
> However, if he had actually had any real knowledge,
> he would have suggested that you use a static
> variable on your Customer class, which would be ideal
> for what you are trying to do... like this
A static int would work here, but you would be much better off accessing (and changing) it through a synchronized method. Your way of using it makes it no longer Thread Safe. Whether, or not, he ever intends to make it Threadable is irrelevant. You never know what the future may bring.
>
> public class Customer {
>
> private static int nextID = 1;
>private int customerID;
>
>
> public Customer() {
>
> customerID = nextID++;
> System.out.println("my id:" + customerID);
>
>}
>
> }
Hi,
i think you both are right: My question was not that smart. ;-)
Thanks for help though.
The thing is thati want to get the customerID from a database, for that i created this NextIds class which is in my first post.
This class has to be abstract, because i am using this InjectProperty Thing to get access to an hivemind service which opens a hibernate session to access the database.
I just found out that th error has nothing to do with the customer class.
I get the error when calling this nextid.getnextcustomerid() function which tries to access the database, and for some reason there i get a nullpointer exeption, i dont know why. I think its another topic.
This is my error:
Stack Trace:
* com.nuromobile.accounting.DomainObjects.Customer.<init>(Customer.java:42)
* com.nuromobile.accounting.misc.Insert.pageBeginRender(Insert.java:65)
* org.apache.tapestry.AbstractPage.firePageBeginRender(AbstractPage.java:478)
* org.apache.tapestry.AbstractPage.renderPage(AbstractPage.java:268)
* org.apache.tapestry.engine.RequestCycle.renderPage(RequestCycle.java:366)
* org.apache.tapestry.services.impl.ResponseRendererImpl.renderResponse(ResponseRendererImpl.java:71)
* $ResponseRenderer_10ec1e26caa.renderResponse($ResponseRenderer_10ec1e26caa.java)
* $ResponseRenderer_10ec1e26ca9.renderResponse($ResponseRenderer_10ec1e26ca9.java)
* org.apache.tapestry.engine.PageService.service(PageService.java:68)
* $IEngineService_10ec1e26e9c.service($IEngineService_10ec1e26e9c.java)
* org.apache.tapestry.services.impl.EngineServiceInnerProxy.service(EngineServiceInnerProxy.java:77)
* org.apache.tapestry.services.impl.EngineServiceOuterProxy.service(EngineServiceOuterProxy.java:66)
* org.apache.tapestry.engine.AbstractEngine.service(AbstractEngine.java:248)
* org.apache.tapestry.services.impl.InvokeEngineTerminator.service(InvokeEngineTerminator.java:60)
* $WebRequestServicer_10ec1e26e76.service($WebRequestServicer_10ec1e26e76.java)
* $WebRequestServicer_10ec1e26e75.service($WebRequestServicer_10ec1e26e75.java)
* org.apache.tapestry.services.impl.DisableCachingFilter.service(DisableCachingFilter.java:48)
* $WebRequestServicerFilter_10ec1e26e78.service($WebRequestServicerFilter_10ec1e26e78.java)
* $WebRequestServicerFilter_10ec1e26e77.service($WebRequestServicerFilter_10ec1e26e77.java)
* $WebRequestServicer_10ec1e26e79.service($WebRequestServicer_10ec1e26e79.java)
* $WebRequestServicer_10ec1e26e72.service($WebRequestServicer_10ec1e26e72.java)
* $WebRequestServicer_10ec1e26e71.service($WebRequestServicer_10ec1e26e71.java)
* org.apache.tapestry.services.impl.WebRequestServicerPipelineBridge.service(WebRequestServicerPipelineBridge.java:56)
* $ServletRequestServicer_10ec1e26e58.service($ServletRequestServicer_10ec1e26e58.java)
* $ServletRequestServicer_10ec1e26e57.service($ServletRequestServicer_10ec1e26e57.java)
* org.apache.tapestry.request.DecodedRequestInjector.service(DecodedRequestInjector.java:55)
* $ServletRequestServicerFilter_10ec1e26e54.service($ServletRequestServicerFilter_10ec1e26e54.java)
* $ServletRequestServicerFilter_10ec1e26e53.service($ServletRequestServicerFilter_10ec1e26e53.java)
* $ServletRequestServicer_10ec1e26e59.service($ServletRequestServicer_10ec1e26e59.java)
* org.apache.tapestry.multipart.MultipartDecoderFilter.service(MultipartDecoderFilter.java:52)
* $ServletRequestServicerFilter_10ec1e26e52.service($ServletRequestServicerFilter_10ec1e26e52.java)
* $ServletRequestServicerFilter_10ec1e26e51.service($ServletRequestServicerFilter_10ec1e26e51.java)
* $ServletRequestServicer_10ec1e26e59.service($ServletRequestServicer_10ec1e26e59.java)
* org.apache.tapestry.services.impl.SetupRequestEncoding.service(SetupRequestEncoding.java:53)
* $ServletRequestServicerFilter_10ec1e26e56.service($ServletRequestServicerFilter_10ec1e26e56.java)
* $ServletRequestServicerFilter_10ec1e26e55.service($ServletRequestServicerFilter_10ec1e26e55.java)
* $ServletRequestServicer_10ec1e26e59.service($ServletRequestServicer_10ec1e26e59.java)
* $ServletRequestServicer_10ec1e26cca.service($ServletRequestServicer_10ec1e26cca.java)
* $ServletRequestServicer_10ec1e26cc9.service($ServletRequestServicer_10ec1e26cc9.java)
* org.apache.tapestry.ApplicationServlet.doService(ApplicationServlet.java:123)
* org.apache.tapestry.ApplicationServlet.doGet(ApplicationServlet.java:79)
* javax.servlet.http.HttpServlet.service(HttpServlet.java:689)
* javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
* org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:252)
* org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
* org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
* org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:178)
* org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:126)
* org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:105)
* org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:107)
* org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:148)
* org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:869)
* org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:664)
* org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:527)
* org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:80)
* org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:684)
* java.lang.Thread.run(Thread.java:595)
Well done masijade. Now you actually got round to letting a bit of your knowledge scrape off. That's what forums are for. Shame it took someone like me to 'ride in' and remind you what forums are for.
As for your pretentious guff about making things Thread safe - now you just sound desperate. Do you really make every method you ever write thread safe? I doubt it. You sound like one of those code monkeys who has to justify to their boss why they take so long over the simpest task. Which is probably what you are. Why else would you hang around in the newbie forums trying to put down people who are starting out? Maybe you should learn to help and guide others - that way you might end up being the organ grinder instead of the monkey. Good luck with that. :)
In the meantime, why don't you try demonstrating your superior knowledge by helping Fabb to solve his error? I'm sure it will be easy for you right?
Message was edited by:
T_1969
> Well done masijade. Now you actually got round to
> letting a bit of your knowledge scrape off. That's
> what forums are for. Shame it took someone like me to
> 'ride in' and remind you what forums are for.
>
> As for your pretentious guff about making things
> Thread safe - now you just sound desperate. Do you
> really make every method you ever write thread safe?
> I doubt it. You sound like one of those code monkeys
> who has to justify to their boss why they take so
> long over the simpest task. Which is probably what
> you are. Why else would you hang around in the newbie
> forums trying to put down people who are starting
> out? Maybe you should learn to help and guide others
> - that way you might end up being the organ grinder
> instead of the monkey. Good luck with that. :)
>
> In the meantime, why don't you try demonstrating your
> superior knowledge by helping Fabb to solve his
> error? I'm sure it will be easy for you right?
>
> Message was edited by:
> T_1969
Because his problem has to do with Hibernate, which I do not use. If you want to enter those waters go ahead.
As far as your ranting at me, go ahead and act the troll. I could care less.
Haha. im actually laughing at your predictable response. As I suspected, you don't really know much. I'll let you get back to crowing over the easy mistakes you understand.
Ther are too many unhelpful twats like you around this forum. Nice to see one getting their bluff called..and yes..you clearly could care less.
I don't know how having no experience with Hibernate has to do with not knowing anything, but I don't see you saying much, so who's bluff is being called?
I am at least willing to say I don't use Hibernate so I am not going to take the time to try and investigate all that much further. You are not.
I don't see any Hibernate here.
Actually, masijade's point is correct - what DID the OP expect? Not only is the reference null, but NextIds is an abstract class. Where's the concrete implementation?
The answer depends on how IDs are generated for objects. If you're using Oracle or PostgreSQL, you're likely to generate them from a sequence. You have to do a SQL query to SELECT sequence_name.NEXTVAL FROM DUAL in Oracle to get the next sequence value.
If you're doing it on your own you have to write a method that will return a value that you generate. You can generate that using java.util.UUID.
%
> However, if he had actually had any real knowledge,
> he would have suggested that you use a static
> variable on your Customer class, which would be ideal
> for what you are trying to do... like this
Ideal - until the app stops and starts again. Then your IDs go back to the beginning, and you'll violate referential integrity constraints.
I would not recommend that you follow this advice.
%
>but I don't see you saying much, so who's bluff is being called?
When exactly did I claim to know it all? I'm in the newbie forum because I'm new to Java. But I'm not the one putting people down for making simple mistakes. If your code is as **** as your logic, no wonder you have so much time to spend in forums. Be honest, have you ever actually programmed for money?
Whatever you say, calling you out on this has made a difference, because I've just seen you give an exemplary answer to someone whose problem was a missing = sign, which is a much more basic mistake. So it worked. Now just try to keep up with being helpful, because in the end, it makes you look much more knowledgeable than just making crass comments to newbies.
> I don't see any Hibernate here.
>
Well, he mentioned Hibernate, and the stacktrace didn't tell me anything other than it seems to be running under Tomcat, so I just simply said hands off. A little short-sighted and/or premature I will admit, but it's what I did.
Edit:
Removed unnecessary quote.
> >but I don't see you saying much, so who's bluff is
> being called?
>
> When exactly did I claim to know it all? I'm in the
> newbie forum because I'm new to Java. But I'm not the
> one putting people down for making simple mistakes.
> If your code is as **** as your logic, no wonder you
> have so much time to spend in forums. Be honest, have
> you ever actually programmed for money?
>
> Whatever you say, calling you out on this has made a
> difference, because I've just seen you give an
> exemplary answer to someone whose problem was a
> missing = sign, which is a much more basic mistake.
> So it worked. Now just try to keep up with being
> helpful, because in the end, it makes you look much
> more knowledgeable than just making crass comments to
> newbies.
And if you would take the time to look through histories, you would see that that response is my normal response, but no, you just simply want to pull the trigger and let it go.
And by the way, you were the one saying no experience with a product equated to no knowledge, so I don't see what complaining about with being a "newbie".
>Ideal - until the app stops and starts again. Then your IDs go back to the beginning, and you'll violate referential integrity constraints.
who said this would be a problem? He is getting the actual customer ID from a sql database - I presumed he just needs an internal reference to give them a position in the list or something. It's funny how masijade starts out being so unhelpful, but when someone like me calls him out on it, you guys are now trying to solve problems this guy hasn't even encountered yet. Maybe you need showing up more often - it seems to have made you sit up and discuss these things at least, which is what you could have done in the first place without having to have your pride pricked. Lol.
> >Ideal - until the app stops and starts again. Then
> your IDs go back to the beginning, and you'll violate
> referential integrity constraints.
>
> who said this would be a problem? He is getting the
> actual customer ID from a sql database - I presumed
> he just needs an internal reference to give them a
> position in the list or something. It's funny how
> masijade starts out being so unhelpful, but when
> someone like me calls him out on it, you guys are now
> trying to solve problems this guy hasn't even
> encountered yet. Maybe you need showing up more often
> - it seems to have made you sit up and discuss these
> things at least, which is what you could have done in
> the first place without having to have your pride
> pricked. Lol.
You haven't shown up anyone yet. And my pride, at least, is not pricked. You simply need to look at my history.
So have you actually ever programmed for money? :P
No - right now you are wasting your employer's money trying to lord it over newbies in an internet forum. Which is why you still have to work for a living...
Let's look over some of your recent 'helpful' posts...since you asked me to.
>>But, seriously, do your own homework, or at least make an effort.
Try to code something, if you have a problem, post the problem code here and ask a specific question, otherwise, just go away.
>>You are also free to wear your underwear as a hat, but it is not effective, it is ackward, and it serves no real purpose.
>>When are you finally going to look at the link sabre150 keeps posting to you and download the FTPClient there. Once you download it, read its Guide, API, and Tutorial Documentation and you will have all the information you need. Is that now clear enough for you? Do you need someone to hold your hand and click your mouse?
>>It looks to be a simple loop with a couple of arithmetic operations. Try programming something based on that and, if you have problems, post your code ans ask a real question.
Yeah masijade - you are a really helpful guy. Lol.
I can only speak for myself:T_1969, your trolling is less than entertaining.masijade, thanks for all the help you have provided on this forum.
zadoka at 2007-7-21 12:43:02 >
> who said this would be a problem? He is getting the
> actual customer ID from a sql database
It looks to me like he's creating a new Customer in the constructor and wants to set the primary key value when he does it.
> I presumed
> he just needs an internal reference to give them a
> position in the list or something.
I don't think you're correct. What list? I don't see a list in anyone's code.
> It's funny how
> masijade starts out being so unhelpful,
masijade WAS helpful. The guy asked why he got an NPE, and masijade told him. What's wrong with that?
> but when
> someone like me calls him out on it,
It's not about calling him out, it's about providing correct advice. I think there's an argument to be made that masijade did just that.
> you guys are now
> trying to solve problems this guy hasn't even
> encountered yet.
But you don't have to read between the lines very deeply to see that he's trying to initialize the primary key of a persistent object.
> Maybe you need showing up more often
I've shown up here more than a few times.
> - it seems to have made you sit up and discuss these
> things at least, which is what you could have done in
> the first place without having to have your pride
> pricked. Lol.
"pride pricked"?
I think we are discussing the problem. You're the one who's going off.
And not providing anything that's useful, I might add.
%
Not sure what trolling is, and not trying to entertain. This is a serious point. Which of masijanes above posts do you consider to have been helpful?
It's clear that there are a number of regular posters who use this forum to massage each other's egos and make 'clever' put-downs to newbies. I'm certain that's not what Sun intended this forum to be for, and I'm just speaking up for all the people masijane and others think it is clever to put down. Sorry you don't find that entertaining.
Message was edited by:
T_1969
> Not sure what trolling is, and not trying to
> entertain. This is a serious point. Which of
> masijanes above posts do you consider to have been
> helpful?
The first post he made.
The OP asked:
My error is:
java.lang.NullPointerException
How can i call functionality in the constructor to get the next CustomerID? Is it the right way to do it in the constructor?
The first post that he made pointed out that the object on which he invoked the method was null. I subsequently pointed out that it was abstract, so it could never be instantiated. Both points are germane to the discussion.
> It's clear that there are a number of regular posters
> who use this forum to massage each other's egos
Nope. Speaking only for myself, I'm here to answer questions when I can, learn from those I can't, and have a sense of community with the people that I come to know well. It has nothing to do with ego.
> and make 'clever' put-downs to newbies.
I don't think masijane's response is a "put down". It's a statement of fact laced with a little sarcasm.
Most newbies, like you, tend to be very thin-skinned about criticism of anything they do. They tend to react with moral outrage when their mistakes are pointed out OR when people here refuse to spoon feed them.
> I'm certain
> that's not what Sun intended this forum to be for,
> and I'm just speaking up for all the people masijane
> and others think it is clever to put down. Sorry you
> don't find that entertaining.
Neither entertaining nor helpful.
It's funny, but the OP doesn't seem nearly as upset as you do. Why are you taking all this so personally? Is your ego the one that needs massaging?
%
This is like squeezing a spot.
Thanks for your concern about my ego, but it's big enough to compete with those around here.
I notice none of you have made any attempt to answer the question once it was clear it wasn't straightforward though.
As for why Fabb isn't bothered - I suspect he has gone to find a forum where he can find people with more knowledge who are less worried about sharing it.
As to why I am so 'sensitive' - whatever you might have concluded, I am certainly not new to programming, even though I have only just started getting into Java. Maybe I'm a product of a hippy generation, but I would expect anyone to show common courtesy to someone who has paid them the compliment of asking them for their advice. But as you say youself, masijane's response was laced with unncessary sarcasm. It wasn't always so, and it is becoming more common all the time. It also seems particularly prevalent in Java forums - more so than any other language I have been involved in. Having seen your various responses, I now have a pretty shrewd idea why.
> I am certainly not new to programming, even though > I have only just started getting into Java.> It also seems particularly prevalent in Java forums - more so than> any other language I have been involved in. Maybe Java is just not for you then.
zadoka at 2007-7-21 12:43:02 >
> This is like squeezing a spot.
I'm not familiar with that phrase.
> Thanks for your concern about my ego, but it's big
> enough to compete with those around here.
I'm not concerned, and it's obvious that it's big enough.
> I notice none of you have made any attempt to answer
> the question once it was clear it wasn't
> straightforward though.
Actually, I did. I think that the primary key issue IS addressed by my Oracle and UUID recommendations. Those are possible implementations of his nextIds method, neither of which depends on your static class member solution.
> As for why Fabb isn't bothered - I suspect he has
> gone to find a forum where he can find people with
> more knowledge who are less worried about sharing
> it.
So you're admitting that you aren't knowledgable enough to keep him here?
> As to why I am so 'sensitive' - whatever you might
> have concluded, I am certainly not new to
> programming,
I can't draw that conclusion from what I've seen.
> even though I have only just started
> getting into Java. Maybe I'm a product of a hippy
> generation,
Hippies weren't always so nice.
I'd say there are a lot of people who are far too thin-skinned.
> but I would expect anyone to show common
> courtesy to someone who has paid them the compliment
> of asking them for their advice.
It's not always a compliment here. Lots of people seem to treat free help as an entitlement that does not require responsibility on their part.
> But as you say
> youself, masijane's response was laced with
> unncessary sarcasm.
I said there was sarcasm, but I didn't say it was unnecessary.
> It wasn't always so, and it is
> becoming more common all the time. It also seems
> particularly prevalent in Java forums - more so than
> any other language I have been involved in. Having
> seen your various responses, I now have a pretty
> shrewd idea why.
Shrewd - that's you.
%
> Yeah masijade - you are a really helpful guy. Lol.
You know, this is like statistics. You can make them say whatever you want when you isolate quotes. Read those threads. Most of them were shameless postings of an assignment with a "Do it for me" question/demand. I see no reason to be polite on those.
The underwear comment was in response to dizzy (read her history) and was meant to make a statement and be mildly amusing, and a little mean (once again read her history).
And the FTP quote was to someone who keep posting the same question in new posts simply because he didn't like that he would have to read something for himself, rather than getting a complete solution to something that was not even a problem.
So like I said, read my history. Those that deserve it, get polite help. Those that don't, don't. I also have an occassional peevish moment (like my first post here), that's human nature, but even those are quite mild as compared to many of the others who post here.
zodak and duffymo: Thanks for the support.
Now T_1969 don't go away mad, just go away. And bring your politeness crusade to some other site.
Edit:
To Fabb81, I hope aou get your problem solved, but it doesn't look as though it is going to happen in this thread.
