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• Ruby 1.9 GarbageCollector, GC.disable/enable

  - by seb

  I'm developing a Rails 2.3, Ruby 1.9.1 webapplication that does quite a bunch of calculation before each request. For every request it has to calculate a graph with 300 nodes and ~1000 edges. The graph and all its nodes, edges and other objects are initialized for every request (~2000 objects) - actually they are cloned from an uncalculated cached graph using Marshal.load(Marshal.dump()). Performance is quite an issue here. Right now the whole request takes in average 150ms. I then saw that during a request, parts of the calculation randomly take longer. Assuming, that this might be the GarbageCollector kicking in, I wrapped the request in GC.disable and GC.enable, so that the request waits with garbagecollecting until calculating and rendering have finished. def query GC.disable calculate respond_to do |format| format.html {render} end GC.enable end The average request now takes about 100ms (50 ms less). But I'm unsure if this is a good/stable solution, I assume there must be drawbacks doing that. Does anybody has experience with a similar problem or sees problems with the above code?

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• retrieving object information with Doctrine

  - by ajsie

  i want to fetch information from the database using objects. i really like this approach cause this is more OOP: $user = Doctrine_Core::getTable('User')->find(1); echo $user->Email['address']; echo $user->Phonenumbers[0]->phonenumber; rather than: $q = Doctrine_Query::create() ->from('User u') ->leftJoin('u.Email e') ->leftJoin('u.Phonenumbers p') ->where('u.id = ?', 1); $user = $q->fetchOne(); echo $user->Email['address']; echo $user->Phonenumbers[0]['phonenumber']; the problem is that the first one uses 3 queries (3 different tables), while the second one uses only 1 (and is therefore recommended technique). but i feel that it destroys the object oriented design. cause ORM is meant to give us an OOP approach so that we could focus on objects and not the relational database. but now they want us to go back to use SQL like pattern. there isn't a way to get information form multiple tables not using DQL? the above examples are taken from the documentation: doctrine

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• Opaque tenant identification with SQL Server & NHibernate

  - by Anton Gogolev

  Howdy! We're developing a nowadays-fashionable multi-tenanted SaaS app (shared database, shared schema), and there's one thing I don't like about it: public class Domain : BusinessObject { public virtual long TenantID { get; set; } public virtual string Name { get; set; } } The TenantID is driving me nuts, as it has to be accounted for almost everywhere, and it's a hassle from security standpoint: what happens if a malicious API user changes TenantID to some other value and will mix things up. What I want to do is to get rid of this TenantID in our domain objects altogether, and to have either NHibernate or SQL Server deal with it. From what I've already read on the Internets, this can be done with CONTEXT_INFO (here's a NHibernatebased implementation), NHibernate filters, SQL Views and with combination thereof. Now, my requirements are as follows: Remove any mentions of TenantID from domain objects ...but have SQL Server insert it where appropriate (I guess this is achieved with default constraints) ...and obviously provide support for filtering based on this criteria, so that customers will never see each other's data If possible, avoid SQL Server views. Have a solution which plays nicely with NHibernate, SQL Servers' MARS and general nature of SaaS apps being highly concurrent What are your thoughts on that?

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• NSTask executed only once

  - by Eimantas

  I'm having trouble executing different NSTask's. Same launchPath, different arguments. I have a class who's instances administer own NSTask objects and depending on arguments those instances were initialized with - dependent NSTask object is being created. I have two initializers: // Method for finished task - (void)taskFinished:(NSNotification *)aNotification { [myTask release]; myTask = nil; [self createTask]; } // Designated initializer - (id) init { self = [super init]; if (self != nil) { [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(taskFinished:) name:NSTaskDidTerminateNotification object:nil]; [self createTask]; } return self; } // Convenience initializer - (id)initWithCommand:(NSString *)subCommand { self = [self init]; if (self) { [self setCommand:subCommand]; } return self; } And here 's the createTask method: - (void)createTask { // myTask is a property defined as NSTask* myTask = [[NSTask alloc] init]; [myTask setLaunchPath:@"/usr/bin/executable"]; } Say I have 3 buttons. Each one creates different class instance with different NSTask objects. But problem is that only first one gets executed. The second ones does not even triger "click" event (via target-action). I think it could be cause of launchPath I'm trying to use, 'cause simple /bin/ls works fine. The same command in terminal has 0 return value (i.e. all is fine). Any guides or gotchas are much appreciated.

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• How do I show TextView's in LinearLayout that layed on other Layout?

  - by gelassen

  Good day. I have three layouts: first is the root, second and third lie in first. I try add TextView object in third layout and objects had been added in third layout (I saw it in debage mode) but this objects didn't showed on screen. May be someone know where is the problem? <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="fill_parent" android:orientation="vertical"> <LinearLayout android:layout_width="fill_parent" android:layout_height="wrap_content" android:orientation="horizontal"> <Button android:id="@+id/addJokeButton" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="@string/app_name" /> <EditText android:id="@+id/newJokeEditText" android:layout_width="fill_parent" android:layout_height="wrap_content" /> </LinearLayout> <LinearLayout android:layout_width="fill_parent" android:layout_height="fill_parent" android:orientation="vertical"> </LinearLayout> </LinearLayout> protected void initLayout() { setContentView(R.layout.advanced); LinearLayout linearLayout = (LinearLayout) getLayoutInflater().inflate( R.layout.advanced, null); m_vwJokeEditText = (EditText) findViewById(R.id.newJokeEditText); m_vwJokeButton = (Button) findViewById(R.id.addJokeButton); m_vwJokeLayout = (LinearLayout) linearLayout.getChildAt(1); } protected void addJoke(Joke joke) { m_arrJokeList.add(joke); LayoutParams lparams = new LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT); TextView textView = new TextView(this); setColor(textView); textView.setLayoutParams(lparams); textView.setText(joke.getJoke()); m_vwJokeLayout.addView(textView); }

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• Change classes instantiated with loadNibNamed

  - by Nick H247

  I am trying to change the class of objects created with a nib with the iPhone SDK. The reason for this is; i dont know until runtime what the class is that i want the nib object to be (though they will have the same UIView based super class), and i dont want to create a different nib for every eventuality - as the .nib will be the same for each, apart from the class of one object. I have been successful, with a couple of methods, but either have some knock on effects or am unsure of how safe the methods I have used are: Method 1: Override alloc, on the super class and set a c variable to the class I require: + (id) alloc { if (theClassIWant) { id object = [theClassIWant allocWithZone:NSDefaultMallocZone()]; theClassIWant = nil; return object; } return [BaseClass allocWithZone:NSDefaultMallocZone()]; } this works well, and i assume is 'reasonably' safe, though if I alloc a subclass myself (without setting 'theClassIWant') - an object of the base class is created. I also dont really like the idea of overriding alloc... Method 2: use object_setClass(self,theClassIWant) in initWithCoder (before calling initWithCoder on the super class): - (id) initWithCoder:(NSCoder *)aDecoder { if (theClassIWant) { // the framework doesn't like this: //[self release]; //self = [theClassIWant alloc]; // whoa now! object_setClass(self,theClassIWant); theClassIWant = nil; return [self initWithCoder:aDecoder]; } if (self = [super initWithCoder:aDecoder]) { ... this also works well, but not all the subclasses are necessarily going to be the same size as the super class, so this could be very unsafe! To combat this i tried releasing and re-allocing to the correct type within initWithCoder, but i got the following error from the framework: "This coder requires that replaced objects be returned from initWithCoder:" dont quite get what this means! i am replacing an object in initWithCoder... Any comments on the validity of these methods, or suggestions of improvements or alternatives welcome!

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• Accessing running task scheduled with java.util.Timer

  - by jbatista

  I'm working on a Java project where I have created a class that looks like this (abridged version): public class Daemon { private static Timer[] timerarray=null; private static Daemon instance=null; protected Daemon() { ArrayList<Timer> timers = new ArrayList<Timer>(); Timer t = new Timer("My application"); t.schedule(new Worker(), 10000,30000); timers.add(t); //... timerarray = timers.toArray(new Timer[]{}); } public static Daemon getInstance() { if(instance==null) instance=new Daemon(); return instance; } public SomeClass getSomeValueFromWorker() { return theValue; } ///////////////////////////////////////////// private class Worker extends TimerTask { public Worker() {} public void run() { // do some work } public SomeReturnClass someMethod(SomeType someParameter) { // return something; } } ///////////////////////////////////////////// } I start this class, e.g. by invoking daemon.getInstance();. However, I'd like to have some way to access the running task objects' methods (for example, for monitoring the objects' state). The Java class java.util.Timer does not seem to provide the means to access the running object, it just schedules the object instance extending TimerTask. Are there ways to access the "running" object instanciated within a Timer? Do I have to subclass the Timer class with the appropriate methods to somehow access the instance (this "feels" strange, somehow)? I suppose someone might have done this before ... where can I find examples of this "procedure"? Thank you in advance for your feedback.

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• Advantages/Disadvantages of AIR vs Flex/Web

  - by Lizzan

  Hi all, I'm tasked with writing an application for placing and connecting objects (sort of like a room planner where you can place furniture). I've made a demo using Flash Builder 4 and built it for AIR as a desktop app. Now the client wants the full app, but they and I am unsure whether to continue building it as an AIR app or transform it to a web application using Flex. I tried making a simple conversion of the AIR app to a web app, and most things worked but not all. The things that don't work seem to be simple bugs, though, not complete lack of capability. The capabilities that I'm going to need (except for the modelling) are: Printing of the finished image + a list of the furniture that has been placed A way to save and retrieve finished plans A way to export the list of furniture to Excel format Handling a whole slew of data about the different objects Only the printing has been implemented so far, and seems to work in the web app as well. What advantages/disadvantages are there with the two approaches? Are any of the capabilities I need much worse (or even impossible) to implement in either approach?

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• Cant' cast a class with multiple inheritance

  - by Jay S.

  I am trying to refactor some code while leaving existing functionality in tact. I'm having trouble casting a pointer to an object into a base interface and then getting the derived class out later. The program uses a factory object to create instances of these objects in certain cases. Here are some examples of the classes I'm working with. // This is the one I'm working with now that is causing all the trouble. // Some, but not all methods in NewAbstract and OldAbstract overlap, so I // used virtual inheritance. class MyObject : virtual public NewAbstract, virtual public OldAbstract { ... } // This is what it looked like before class MyObject : public OldAbstract { ... } // This is an example of most other classes that use the base interface class NormalObject : public ISerializable // The two abstract classes. They inherit from the same object. class NewAbstract : public ISerializable { ... } class OldAbstract : public ISerializable { ... } // A factory object used to create instances of ISerializable objects. template<class T> class Factory { public: ... virtual ISerializable* createObject() const { return static_cast<ISerializable*>(new T()); // current factory code } ... } This question has good information on what the different types of casting do, but it's not helping me figure out this situation. Using static_cast and regular casting give me error C2594: 'static_cast': ambiguous conversions from 'MyObject *' to 'ISerializable *'. Using dynamic_cast causes createObject() to return NULL. The NormalObject style classes and the old version of MyObject work with the existing static_cast in the factory. Is there a way to make this cast work? It seems like it should be possible.

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• Unboxing to unknown type

  - by Robert

  I'm trying to figure out syntax that supports unboxing an integral type (short/int/long) to its intrinsic type, when the type itself is unknown. Here is a completely contrived example that demonstrates the concept: // Just a simple container that returns values as objects struct DataStruct { public short ShortVale; public int IntValue; public long LongValue; public object GetBoxedShortValue() { return LongValue; } public object GetBoxedIntValue() { return LongValue; } public object GetBoxedLongValue() { return LongValue; } } static void Main( string[] args ) { DataStruct data; // Initialize data - any value will do data.LongValue = data.IntValue = data.ShortVale = 42; DataStruct newData; // This works if you know the type you are expecting! newData.ShortVale = (short)data.GetBoxedShortValue(); newData.IntValue = (int)data.GetBoxedIntValue(); newData.LongValue = (long)data.GetBoxedLongValue(); // But what about when you don't know? newData.ShortVale = data.GetBoxedShortValue(); // error newData.IntValue = data.GetBoxedIntValue(); // error newData.LongValue = data.GetBoxedLongValue(); // error } In each case, the integral types are consistent, so there should be some form of syntax that says "the object contains a simple type of X, return that as X (even though I don't know what X is)". Because the objects ultimately come from the same source, there really can't be a mismatch (short != long). I apologize for the contrived example, it seemed like the best way to demonstrate the syntax. Thanks.

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• OO vs Simplicity when it comes to user interaction

  - by Oetzi

  Firstly, sorry if this question is rather vague but it's something I'd really like an answer to. As a project over summer while I have some downtime from Uni I am going to build a monopoly game. This question is more about the general idea of the problem however, rather than the specific task I'm trying to carry out. I decided to build this with a bottom up approach, creating just movement around a forty space board and then moving on to interaction with spaces. I realised that I was quite unsure of the best way of proceeding with this and I am torn between two design ideas: Giving every space its own object, all sub-classes of a Space object so the interaction can be defined by the space object itself. I could do this by implementing different land() methods for each type of space. Only giving the Properties and Utilities (as each property has unique features) objects and creating methods for dealing with the buying/renting etc in the main class of the program (or Board as I'm calling it). Spaces like go and super tax could be implemented by a small set of conditionals checking to see if player is on a special space. Option 1 is obviously the OO (and I feel the correct) way of doing things but I'd like to only have to handle user interaction from the programs main class. In other words, I don't want the space objects to be interacting with the player. Why? Errr. A lot of the coding I've done thus far has had this simplicity but I'm not sure if this is a pipe dream or not for larger projects. Should I really be handling user interaction in an entirely separate class? As you can see I am quite confused about this situation. Is there some way round this? And, does anyone have any advice on practical OO design that could help in general?

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• Serializing QGraphicsScene contents

  - by Rob

  I am using the Qt QGraphicsScene class, adding pre-defined items such as QGraphicsRectItem, QGraphicsLineItem, etc. and I want to serialize the scene contents to disk. However, the base QGraphicsItem class (that the other items I use derive from) doesn't support serialization so I need to roll my own code. The problem is that all access to these objects is via a base QGraphicsItem pointer, so the serialization code I have is horrible: QGraphicsScene* scene = new QGraphicsScene; scene->addRect(QRectF(0, 0, 100, 100)); scene->addLine(QLineF(0, 0, 100, 100)); ... QList<QGraphicsItem*> list = scene->items(); foreach (QGraphicsItem* item, items) { if (item->type() == QGraphicsRectItem::Type) { QGraphicsRectItem* rect = qgraphicsitem_cast<QGraphicsRectItem*>(item); // Access QGraphicsRectItem members here } else if (item->type() == QGraphicsLineItem::Type) { QGraphicsLineItem* line = qgraphicsitem_cast<QGraphicsLineItem*>(item); // Access QGraphicsLineItem members here } ... } This is not good code IMHO. So, instead I could create an ABC class like this: class Item { public: virtual void serialize(QDataStream& strm, int version) = 0; }; class Rect : public QGraphicsRectItem, public Item { public: void serialize(QDataStream& strm, int version) { // Serialize this object } ... }; I can then add Rect objects using QGraphicsScene::addItem(new Rect(,,,)); But this doesn't really help me as the following will crash: QList<QGraphicsItem*> list = scene->items(); foreach (QGraphicsItem* item, items) { Item* myitem = reinterpret_class<Item*>(item); myitem->serialize(...) // FAIL } Any way I can make this work?

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• How do I programmatically insert rows into a Silverlight DataGrid without binding?

  - by j0rd4n

  I am using a common Silverlight DataGrid to display results from a search. The "schema" of the search can vary from query to query. To accommodate this, I am trying to dynamically populate the DataGrid. I can set explicitly set the columns, but I am having trouble setting the ItemSource. All of the MSDN examples set the ItemSource to a collection with a strong type (e.g. a Custom type with public properties matching the schema). The DataGrid then uses reflection to scour the strong type for public properties that will match the columns. Since my search results are dynamic, I cannot create a strong type to represent what comes back. Can I not just give the DataGrid an arbitrary list of objects so long as the number of objects in each list matches the number of columns? Anyone know if this is possible? I would like to do something similar to this: List<List<object>> myResults = <voodoo that populates the result list> myDataGrid.ItemsSource = myResults;

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• Google Maps in Drupal: reference to gmap object from JavaScript

  - by user280817

  Is there a way to obtain JavaScript references to the Google maps that are embedded into Drupal pages by the GMap module? I want to be able to manipulate the maps in these pages. I want to pan and zoom them. But I cannot find a reference to an embedded map object. I've dissected the relevant JavaScript objects Drupal.gmap and Drupal.settings.gmap with no success--unless I've overlooked something. The Drupal GMap module doesn't seem to explicitly provide references (within its API) to the GMap objects that it embeds into pages. It just generates themed text which is interpolated into the page. The technique of passing the HTML ID of the map container to either the GMap2 object constructor or the similar Drupal.gmap.getMap() function in order to obtain a map reference doesn't appear to work: Both simply return an instance to a new map, one having the same dimensions and basic characteristics of the original map, but apparently sans all of its overlays (which could contain markers). And I have to call setCenter() on it before I can use it, which initializes the structure, so I know it has no overlays.

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• iPhone: Leak with UIWebView loading Office documents. Any ideas how to avoid it?

  - by Thomas Tempelmann

  While there are already quite a few posts about leaks around UIWebView, mine is a bit more special, I believe, and thus deserves its own post here. I see a reproducible large leak every time I load a Office document such as a Word or Excel file. For instance, every time I display a 180KB .doc file, I get a 100KB leak. And that happens with both the simulator and an actual device, running OS 3.1.3. The leak is not visible with the Leaks instrument but only by looking at the malloc instances via the ObjectAlloc instrument. Here's a picture from the instruments trace: I've also made a demo project, UIWebView-Leak.zip, so you can verify this yourself. To see the leak, use the ObjectAlloc instrument, switch to the view where you see individual allocation objects, and sort by size so that you see the large ones in a group, just like in my picture above. Then view a Office document a few times and find the Malloc objects that keep staying "Live" even after the actual UIWebView has been freed. Is this a known bug? Or is there any way I can avoid these leaks? I.e, have you successfully shown Office documents on an iPhone withing getting such leaks? Note: I've reported this as a bug to Apple now, too (ID 7950594) I am still waiting for someone (including Apple) to confirm this as a true leak or show why it isn't (i.e. that I do something wrong or make wrong assumptions)

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• Is it important to dispose SolidBrush and Pen?

  - by Joe

  I recently came across this VerticalLabel control on CodeProject. I notice that the OnPaint method creates but doesn't dispose Pen and SolidBrush objects. Does this matter, and if so how can I demonstrate whatever problems it can cause? EDIT This isn't a question about the IDisposable pattern in general. I understand that callers should normally call Dispose on any class that implements IDisposable. What I want to know is what problems (if any) can be expected when GDI+ object are not disposed as in the above example. It's clear that, in the linked example, OnPaint may be called many times before the garbage collector kicks in, so there's the potential to run out of handles. However I suspect that GDI+ internally reuses handles in some circumstances (for example if you use a pen of a specific color from the Pens class, it is cached and reused). What I'm trying to understand is whether code like that in the linked example will be able to get away with neglecting to call Dispose. And if not, to see a sample that demonstrated what problems it can cause. I should add that I have very often (including the OnPaint documentation on MSDN) seen WinForms code samples that fail to dispose GDI+ objects.

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• Visual Studio + Database Edition + CDC = Deploy Fail

  - by Ben

  Hi All, I've got a database using change data capture (CDC) that is created from a Visual Studio database project (GDR2). My problem is that I have a stored procedure that is analyzing the CDC information and then returning data. How is that a problem you ask? Well, the order of operation is as follows. Pre-deployment Script Tables Indexes, keys, etc. Procedures Post-deployment Script Inside the post-deployment script is where I enable CDC. Here-in lies the problem. The procedure that is acting on the CDC tables is bombing because they don't exist yet! I've tried to put the call to sys.sp_cdc_enable_table in the script that creates the table, but it doesn't like that. Error 102 TSD03070: This statement is not recognized in this context. C:...\Schema Objects\Schemas\dbo\Tables\Foo.table.sql 20 1 Foo Is there a better/built-in way to enable CDC such that it's references are available when the stored procedures are created? Is there a way to run a script after tables are created but before other objects are created? How about a way to create the procedure dependencies be damned? Or maybe I'm just doing things that shouldn't be done?!?! Now, I have a work around. Comment out the sproc body Deploy (CDC is created) Uncomment sproc Deploy Everything is great until the next time I update a CDC tracked table. Then I need to comment out the 'offending' procedure. Thanks for reading my question and thanks for your help!

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• Is my objective possible using WCF (and is it the right way to do things?)

  - by David

  I'm writing some software that modifies a Windows Server's configuration (things like MS-DNS, IIS, parts of the filesystem). My design has a server process that builds an in-memory object graph of the server configuration state and a client which requests this object graph. The server would then serialize the graph, send it to the client (presumably using WCF), the server then makes changes to this graph and sends it back to the server. The server receives the graph and proceeds to make modifications to the server. However I've learned that object-graph serialisation in WCF isn't as simple as I first thought. My objects have a hierarchy and many have parametrised-constructors and immutable properties/fields. There are also numerous collections, arrays, and dictionaries. My understanding of WCF serialisation is that it requires use of either the XmlSerializer or DataContractSerializer, but DCS places restrictions on the design of my object-graph (immutable data seems right-out, it also requires parameter-less constructors). I understand XmlSerializer lets me use my own classes provided they implement ISerializable and have the de-serializer constructor. That is fine by me. I spoke to a friend of mine about this, and he advocates going for a Data Transport Object-only route, where I'd have to maintain a separate DataContract object-graph for the transport of data and re-implement my server objects on the client. Another friend of mine said that because my service only has two operations ("GetServerConfiguration" and "PutServerConfiguration") it might be worthwhile just skipping WCF entirely and implementing my own server that uses Sockets. So my questions are: Has anyone faced a similar problem before and if so, are there better approaches? Is it wise to send an entire object graph to the client for processing? Should I instead break it down so that the client requests a part of the object graph as it needs it and sends only bits that have changed (thus reducing concurrency-related risks?)? If sending the object-graph down is the right way, is WCF the right tool? And if WCF is right, what's the best way to get WCF to serialise my object graph?

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• django: How to make one form from multiple models containing foreignkeys

  - by Tim

  I am trying to make a form on one page that uses multiple models. The models reference each other. I am having trouble getting the form to validate because I cant figure out how to get the id of two of the models used in the form into the form to validate it. I used a hidden key in the template but I cant figure out how to make it work in the views My code is below: views: def the_view(request, a_id,): if request.method == 'POST': b_form= BForm(request.POST) c_form =CForm(request.POST) print "post" if b_form.is_valid() and c_form.is_valid(): print "valid" b_form.save() c_form.save() return HttpResponseRedirect(reverse('myproj.pro.views.this_page')) else: b_form= BForm() c_form = CForm() b_ide = B.objects.get(pk=request.b_id) id_of_a = A.objects.get(pk=a_id) return render_to_response('myproj/a/c.html', {'b_form':b_form, 'c_form':c_form, 'id_of_a':id_of_a, 'b_id':b_ide }) models class A(models.Model): name = models.CharField(max_length=256, null=True, blank=True) classe = models.CharField(max_length=256, null=True, blank=True) def __str__(self): return self.name class B(models.Model): aid = models.ForeignKey(A, null=True, blank=True) number = models.IntegerField(max_length=1000) other_number = models.IntegerField(max_length=1000) class C(models.Model): bid = models.ForeignKey(B, null=False, blank=False) field_name = models.CharField(max_length=15) field_value = models.CharField(max_length=256, null=True, blank=True) forms from mappamundi.mappa.models import A, B, C class BForm(forms.ModelForm): class Meta: model = B exclude = ('aid',) class CForm(forms.ModelForm): class Meta: model = C exclude = ('bid',) B has a foreign key reference to A, C has a foreign key reference to B. Since the models are related, I want to have the forms for them on one page, 1 submit button. Since I need to fill out fields for the forms for B and C & I dont want to select the id of B from a drop down list, I need to somehow get the id of the B form into the form so it will validate. I have a hidden field in the template, I just need to figure how to do it in the views

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• Partially constructed object / Multi threading

  - by reto

  Heya! I'm using joda due to it's good reputation regarding multi threading. It goes great distances to make multi threaded date handling efficient, for example by making all Date/Time/DateTime objects immutable. But here's a situation where I'm not sure if Joda is really doing the right thing. It probably is correct, but I'd be very interested to see the explanation for it. When a toString() of a DateTime is being called Joda does the following: /* org.joda.time.base.AbstractInstant */ public String toString() { return ISODateTimeFormat.dateTime().print(this); } All formatters are thread safe, as they are as well ready-only. But what's about the formatter-factory: private static DateTimeFormatter dt; /* org.joda.time.format.ISODateTimeFormat */ public static DateTimeFormatter dateTime() { if (dt == null) { dt = new DateTimeFormatterBuilder() .append(date()) .append(tTime()) .toFormatter(); } return dt; } This is a common pattern in single threaded applications. I see the following dangers: Race condition during null check -- worst case: two objects get created. No Problem, as this is solely a helper object (unlike a normal singleton pattern situation), one gets saved in dt, the other is lost and will be garbage collected sooner or later. the static variable might point to a partially constructed object before the objec has been finished initialization (before calling me crazy, read about a similar situation in this Wikipedia article. So how does Joda ensure that not partially created formatter gets published in this static variable? Thanks for your explanations! Reto

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• Write a program which works out which is the lowest priced computer in an ArrayList of computer obje

  - by Eoin

  Hello everybody! I am trying to study some java and cannot get my head around this question! Any help would be really appreciated and would help me in further studies! Thank you so much in advance! Eoin from Dublin, Ireland. ArrayList of Objects Write a program which works out which is the lowest priced computer in an ArrayList of computer objects. You should have two classes, one called ComputerTest, and the other called Computer. In the ComputerTest class you should: Have a main method which declares an ArrayList of type Computer called computerList, each element of which represents a computer. Initialise the first three entries of the ArrayList Call a static method which prints out the lowest price computer, called lowestPrice The parameter of this method is (i) an ArrayList of type Computer i.e. ArrayList data Sample output: The lowest priced computer is the Cheapo400 at 399 euro. The Computer class should have: Private instance variables: manufacturer, model, price and quality. Quality is a rating from 1 to 10. public get and set methods to retrieve and set/change the value of the four instance variables a default constructor a constructor that takes four parameters

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• Using fields from an association (has_many) model with formtastic in rails

  - by pduersteler

  I searched and tried a lot, but I can't accomplish it as I want.. so here's my problem. class Moving < ActiveRecord::Base has_many :movingresources, :dependent => :destroy has_many :resources, :through => :movingresources end class Movingresource < ActiveRecord::Base belongs_to :moving belongs_to :resource end class Resource < ActiveRecord::Base has_many :movingresources has_many :movings, :through => :movingresources end Movingresources contains additional fields, like "quantity". We're working on the views for 'bill'. Thanks to formtastic to simplify the whole relationship thing by just writing <%= form.input :workers, :as => :check_boxes %> and i get a real nice checkbox list. But what I haven't found out so far is: How can i use the additional fields from 'movingresource', next or under each checkbox my desired fields from that model? I saw different approaches, mainly with manually looping through an array of objects and creating the appropriate forms, using :for in a form.inputs part, or not. But none of those solutions were clean (e.g. worked for the edit view but not for new because the required objects were not built or generated and generating them caused a mess). I want to know your solutions for this! :-)

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• Are there pitfalls to using static class/event as an application message bus

  - by Doug Clutter

  I have a static generic class that helps me move events around with very little overhead: public static class MessageBus<T> where T : EventArgs { public static event EventHandler<T> MessageReceived; public static void SendMessage(object sender, T message) { if (MessageReceived != null) MessageReceived(sender, message); } } To create a system-wide message bus, I simply need to define an EventArgs class to pass around any arbitrary bits of information: class MyEventArgs : EventArgs { public string Message { get; set; } } Anywhere I'm interested in this event, I just wire up a handler: MessageBus<MyEventArgs>.MessageReceived += (s,e) => DoSomething(); Likewise, triggering the event is just as easy: MessageBus<MyEventArgs>.SendMessage(this, new MyEventArgs() {Message="hi mom"}); Using MessageBus and a custom EventArgs class lets me have an application wide message sink for a specific type of message. This comes in handy when you have several forms that, for example, display customer information and maybe a couple forms that update that information. None of the forms know about each other and none of them need to be wired to a static "super class". I have a couple questions: fxCop complains about using static methods with generics, but this is exactly what I'm after here. I want there to be exactly one MessageBus for each type of message handled. Using a static with a generic saves me from writing all the code that would maintain the list of MessageBus objects. Are the listening objects being kept "alive" via the MessageReceived event? For instance, perhaps I have this code in a Form.Load event: MessageBus<CustomerChangedEventArgs>.MessageReceived += (s,e) => DoReload(); When the Form is Closed, is the Form being retained in memory because MessageReceived has a reference to its DoReload method? Should I be removing the reference when the form closes: MessageBus<CustomerChangedEventArgs>.MessageReceived -= (s,e) => DoReload();

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• Poor performance using RMI-proxies with Swing components

  - by Patrick

  I'm having huge performance issues when I add RMI proxy references to a Java Swing JList-component. I'm retrieving a list of user Profiles with RMI from a server. The retrieval itself takes just a second or so, so that's acceptable under the circumstances. However, when I try to add these proxies to a JList, with the help of a custom ListModel and a CellRenderer, it takes between 30-60 seconds to add about 180 objects. Since it is a list of users' names, it's preferrable to present them alphabetically. The biggest performance hit is when I sort the elements as they get added to the ListModel. Since the list will always be sorted, I opted to use the built-in Collections.binarySearch() to find the correct position for the next element to be added, and the comparator uses two methods that are defined by the Profile interface, namely getFirstName() and getLastName(). Is there any way to speed this process up, or am I simply implementing it the wrong way? Or is this a "feature" of RMI? I'd really love to be able to cache some of the data of the remote objects locally, to minimize the remote method calls.

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• Which source control paradigm and solution to embed in a custom editor application?

  - by Greg Harman

  I am building an application that manages a number of custom objects, which may be edited concurrently by multiple users (using different instances of the application). These objects have an underlying serialized representation, and my plan is to persist them (through my application UI) in an external source control system. Of course this implies that my application can check the current version of an object for updates, a merging interface for each object, etc. My question is what source control paradigm(s) and specific solution(s) to support and why. The way I (perhaps naively) see the source control world is three general paradigms: Single-repository, locked access (MS SourceSafe) Single-repository, concurrent access (CVS/SVN) Distributed (Mercurial, Git) I haven't heard of anyone using #1 for quite a number of years, so I am planning to disregard this case altogether (unless I get a compelling argument otherwise). However, I'm at a loss as to whether to support #2 or #3, and which specific implementations. I'm concerned that the use paradigms are subtly different enough that I can't adequately capture basic operations in a single UI. The last bit of information I should convey is that this application is intended to be deployed in a commercial setting, where a source control system may already be in use. I would prefer not to support more than one solution unless it's really a deal-breaker, so wide adoption in a corporate setting is a plus.

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