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• Returning and instance of a Class given its .class (MyClass.class)

  - by jax

  I have an enum that will hold my algorithms. I cannot instantiate these classes because I need the application context which is only available once the application has started. I want to load the class at runtime when I choose by calling getAlgorithm(Context cnx). How do I easily instantiate a class at runtime given its .class (and my constructor takes arguments)? All my classes are subclasses of Algorithm. public enum AlgorithmTypes { ALL_FROM_9_AND_LAST_FROM_10_ID(AlgorithmFactory.AlgorithmAllFrom9AndLastFrom10Impl.class), ALL_FROM_9_AND_LAST_FROM_10_CURRENCY_ID(AlgorithmFactory.AlgorithmAllFrom9AndLastFrom10Impl.class), DIVIDE_BY_9_LESS_THAN_100(AlgorithmFactory.AlgorithmAllFrom9AndLastFrom10Impl.class), TABLES_BEYOND_5_BY_5(AlgorithmFactory.AlgorithmAllFrom9AndLastFrom10Impl.class); private Class<? extends Algorithm> algorithm; AlgorithmTypes(Class<? extends Algorithm> c) { algorithm = c; } public Algorithm getAlgorithm(Context cnx) { return //needs to return the current algoriths constructor which takes the Context Algorithm(Context cnx); } }

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• Rails: Creating subfolders in model?

  - by keruilin

  I'm going to have a ton of subclasses, so want to organize them under a subfolder called stream. I added the following line to the environment.rb so that all classes in the subfolder would be loaded: Rails::Initializer.run do |config| ... config.load_paths += Dir["#{RAILS_ROOT}/app/models/*"].find_all { |f| File.stat(f).directory? } ... end I thought this would solve the issue in which by convention the model class is namespaced into an according module. However, when I try to call one of the classes called stream in the stream folder, I get the following error: NoMethodError: undefined method `new' for Stream:Module from (irb):28 from /usr/local/bin/irb:12:in `<main>' Here's the model for the parent and one child: class Stream end class EventStream < Stream end Any idea what the issue is?

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• So where is this calling super?

  - by dontWatchMyProfile

  From the Core Data docs: Inheritance If you have two subclasses of NSManagedObject where the parent class implements a dynamic property and its subclass (the grandchild of NSManagedObject) overrides the methods for the property, those overrides cannot call super. @interface Parent : NSManagedObject @property(nonatomic, retain) NSString* parentString; @end @implementation Parent @dynamic parentString; @end @interface Child : Parent @end @implementation Child - (NSString *)parentString { // this throws a "selector not found" exception return parentString.foo; } @end very, very funny, because: I see nobody calling super. Or are they? Wait... parentString.foo results in ... a crash ??? it's a string. How can that thing have a .foo suffixed to it? Just another documentation bug?

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• Objectify - Retrieve subclass instances with superclass query

  - by Deviling Master

  for a project i'm making, i'm using Objectify and Google AppEngine I'm quoting and old message from Google Groups, but the problem i have is the same: Here's the problem I'm trying to solve: I'd like to persist instances of several subclasses of one superclass to the datastore, and then retrieve them by querying for that superclass. (For example, a query for Game would return instances of Chess and Backgammon). Is there any way to accomplish this using Objectify? Because the thing i want is the same, but the topic does not provides yet an answer (it's 3 years old), I moved here with the same question. From 2010 to now, this question has been solved? Thanks Bye

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• Java: Is it possible to have a generic class that only takes types that can be compared?

  - by mr popo

  I wanted to do something along the lines of: public class MyClass<T implements Comparable> { .... } But I can't, since, apparently, generics only accept restrictions with subclasses, and not interfaces. It's important that I'm able to compare the types inside the class, so how should I go about doing this? Ideally I'd be able to keep the type safety of Generics and not have to convert the T's to Object as well, or just not write a lot of code overall. In other words, the simplest the better.

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• Add Method to Built In Class

  - by Evorlor

  I am pretty sure this is not doable, but I will go ahead and cross my fingers and ask. I am trying to add a method to a built in class. I want this method to be callable by all of the built in class's subclasses. Specifically: I have a JButton, a JTextPane, and other JComponents. I want to be able to pass in a JDom Element instead of a Rectangle to setBounds(). My current solution is to extend each JComponent subclass with the desired methods, but that is a LOT of duplicate code. Is there a way I can write the following method just one time, and have it callable on all JComponent objects? Or is it required that I extend each subclass individually, and copy and paste the method below? public void setBounds(Element element) { this.setBounds(Integer.parseInt(element.getAttribute( "x").toString()), Integer.parseInt(element .getAttribute("y").toString()), Integer .parseInt(element.getAttribute("width").toString()), Integer.parseInt(element.getAttribute("height") .toString())); }

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• "modal" in apple documentation

  - by Crystal

  Apple uses "modal" often in their documentation. Like dismissModalViewController in their titles of methods, or documentation like: "The UIViewController class provides the fundamental view-management model for iPhone applications. The basic view controller class supports the presentation of an associated view in addition to basic support for managing modal views and rotating views in response to device orientation changes. Subclasses such as UINavigationController and UITabBarController provide additional behavior for managing complex hierarchies of view controllers and views." I'm not sure as to what context I should think of when I see modal in the names and documentation. Any thoughts? Thanks.

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• Compiler error when using abstract types

  - by Dylan

  I'm trying to implement a "protocol helper" trait that is responsible for matching up Prompts and Responses. The eventual goal is to have an object that defines the various Prompt and Response classes as subclasses of a sealed trait, then have a class that mixes in the ProtocolSupport trait for that Protocol object. The problem is that my current approach won't compile, even though I'm fairly sure it should. Here's a distilled version of what I've got: trait Protocol { type Response type Prompt <: BasePrompt trait BasePrompt { type Data def validate(response: Response): Validated[Data] } } trait ProtocolSupport[P <: Protocol] { def foo(prompt: P#Prompt, response: P#Response) = { // compiler error prompt.validate(response) } } The compiler doesn't like the response as an argument to prompt.validate: [error] found : response.type (with underlying type P#Response) [error] required: _4.Response where val _4: P [error] prompt.validate(response) [error] ^ This isn't very helpful.. it seems to say that it wants a P.Response but that's exactly what I'm giving it, so what's the problem?

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• Ruby forwarding method calls

  - by JP

  I have an instance of a master class which generates instances of a subclass, these subclasses need to forward some method calls back to the master instance. At the moment I have code looking something like this, but it feels like I should be able to do the same thing more efficiently (maybe with method_missing?) class Master def initalize(mynum) @mynum = mynum end def one_thing(subinstance) "One thing with #{subinstance.var} from #{@mynum}" end def four_things(subinstance) "Four things with #{subinstance.var} from #{@mynum}" end def many_things(times,subinstance) "#{times} things with #{subinstance.var} from #{@mynum}" end def make_a_sub(uniqueness) Subthing.new(uniqueness,self) end class Subthing def initialize(uniqueness,master) @u = uniqueness @master = master end # Here I'm forwarding method calls def one_thing master.one_thing(self) end def four_things master.four_things(self) end def many_things(times) master.many_things(times,self) end end end m = Master.new(42) s = m.make_a_sub("very") s.one_thing === m.one_thing(s) s.many_things(8) === m.many_things(8,s) I hope you can see what's going on here. I would use method_missing, but I'm not sure how to cope with the possibility of some calls having arguments and some not (I can't really rearrange the order of the arguments to the Master methods either) Thanks for reading!

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• Google App Engine: Difficulty with Users API (or maybe just a Python syntax problem)

  - by Rosarch

  I have a simple GAE app that includes a login/logout link. This app is running on the dev server at the moment. The base page handler gets the current user, and creates a login/logout url appropriately. It then puts this information into a _template_data dictionary, for convenience of subclasses. class BasePage(webapp.RequestHandler): _user = users.get_current_user() _login_logout_link = None if _user: _login_logout_link = users.create_logout_url('/') else: _login_logout_link = users.create_login_url('/') _template_data = {} _template_data['login_logout_link'] = _login_logout_link _template_data['user'] = _user def render(self, templateName, templateData): path = os.path.join(os.path.dirname(__file__), 'Static/Templates/%s.html' % templateName) self.response.out.write(template.render(path, templateData)) Here is one such subclass: class MainPage(BasePage): def get(self): self.render('start', self._template_data) The login/logout link is displayed fine, and going to the correct devserver login/logout page. However, it seems to have no effect - the server still seems to think the user is logged out. What am I doing wrong here?

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• Which class will be instanciated

  - by Michael

  Say I have 2 subclasses from UIViewController, class A and class B. In Main nib file an object is representing class A and it is set to load file from Secondary nib file. The owner of Secondary nib is of class B. The question is - from which class an object in Main nib file will be instanciated once the nib files unarchived in the memory? The reason this question arised is that I have to take care myself if such reference to external NIB file present, to ensure that the first nib's object and second nib's owner is same. Please correct me if my statement is wrong.

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• I want to make a wrapped acces type for certain internals of one of classes and I have some performa

  - by Alex

  I am writing an abstract matrix class (and some concrete subclasses) for use on very differing hardwares/architectures, etc. and I want to write a row and column type that provides a transparent reference to the rows and columns of the matrix. However, I want to tune for performance, so I'd like this class to be essentially a compiler construct. In other words, I'm willing to sacrifice some dev time to making the overhead of these classes as small as possible. I assume all (small) methods would want to be virtual? Keep the structure small? Any other suggestions?

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• port an iOS (iPhone) app to mac?

  - by William Jockusch

  Is there a preferred way to go about this? The app in question is not too large . . . single-player game that I wrote over the course of a couple of months. EDIT: I should add that I have no experience with mac development . . . outside of what comes naturally with being an iOS developer. EDIT: Classes heavily used in the game: subclasses of NSObject, UIView, and UIViewController. I don't know much about NSView, but I'm pretty sure all the UIView stuff will work in that class. Also some use of UITableViewController. I do also have Game Center, but I can leave that part out for now. There is no multi-touch.

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• Ruby - overriding/enabling multiple assignment (e.g. `a, b, c = d, e, f`)

  - by nicholaides

  In ruby, you can do this: d = [1, 2, 3] a, b, c = d a, b, and c, will receive the values 1, 2, and 3, respectively. d, in this case in an Array and ruby knows to assign it's contents to a, b, and c. But, if d were a Fixnum, for example, only a would be assigned to the value of d while b and c would be assigned nil. What properties of d allow it to be used for multiple assignment? In my exploring so far, I've only been able to make instances of subclasses of Array behave in this way.

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• Similar Sub-Classes

  - by praks5432

  Lets say I have a class A that is fairly simple like this - public class A{ private int randomField = 0; protected int key; protected double dmg; } Now I want to write a number of sub-classes that inherit the protected fields and only differ based on the initial values that are assigned to those fields - for example, if I wrote two subclasses B and C, the only difference between those two sub-classes would be that the values key and dmg would have different values. They would share a method, set, which would be exactly the same, in that it would affect the same variable. I find when I'm writing these sub-classes I'm repeating myself, as I just change the constructor to set different initial values to key and dmg, and simply copy and paste the set method. Is there a 'good' way to do this?

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• The Template Method Design Pattern using C# .Net

  - by nijhawan.saurabh

  First of all I'll just put this pattern in context and describe its intent as in the GOF book:   Template Method: Define the skeleton of an algorithm in an operation, deferring some steps to Subclasses. Template Method lets subclasses redefine certain steps of an algorithm without changing the Algorithm's Structure.    Usage: When you are certain about the High Level steps involved in an Algorithm/Work flow you can use the Template Pattern which allows the Base Class to define the Sequence of the Steps but permits the Sub classes to alter the implementation of any/all steps.   Example in the .Net framework: The most common example is the Asp.Net Page Life Cycle. The Page Life Cycle has a few methods which are called in a sequence but we have the liberty to modify the functionality of any of the methods by overriding them.   Sample implementation of Template Method Pattern:   Let's see the class diagram first:            Normal 0 false false false EN-US X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin-top:0in; mso-para-margin-right:0in; mso-para-margin-bottom:8.0pt; mso-para-margin-left:0in; line-height:107%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi; mso-font-kerning:1.0pt; mso-ligatures:standard;}   And here goes the code:EmailBase.cs     1 using System;     2 using System.Collections.Generic;     3 using System.Linq;     4 using System.Text;     5 using System.Threading.Tasks;     6      7 namespace TemplateMethod     8 {     9     public abstract class EmailBase    10     {    11     12         public bool SendEmail()    13         {    14             if (CheckEmailAddress() == true) // Method1 in the sequence    15             {    16                 if (ValidateMessage() == true) // Method2 in the sequence    17                 {    18                     if (SendMail() == true) // Method3 in the sequence    19                     {    20                         return true;    21                     }    22                     else    23                     {    24                         return false;    25                     }    26     27                 }    28                 else    29                 {    30                     return false;    31                 }    32     33             }    34             else    35             {    36                 return false;    37     38             }    39     40     41         }    42     43         protected abstract bool CheckEmailAddress();    44         protected abstract bool ValidateMessage();    45         protected abstract bool SendMail();    46     47     48     }    49 }    50    EmailYahoo.cs      1 using System;     2 using System.Collections.Generic;     3 using System.Linq;     4 using System.Text;     5 using System.Threading.Tasks;     6      7 namespace TemplateMethod     8 {     9     public class EmailYahoo:EmailBase    10     {    11     12         protected override bool CheckEmailAddress()    13         {    14             Console.WriteLine("Checking Email Address : YahooEmail");    15             return true;    16         }    17         protected override bool ValidateMessage()    18         {    19             Console.WriteLine("Validating Email Message : YahooEmail");    20             return true;    21         }    22     23     24         protected override bool SendMail()    25         {    26             Console.WriteLine("Semding Email : YahooEmail");    27             return true;    28         }    29     30     31     }    32 }    33   EmailGoogle.cs      1 using System;     2 using System.Collections.Generic;     3 using System.Linq;     4 using System.Text;     5 using System.Threading.Tasks;     6      7 namespace TemplateMethod     8 {     9     public class EmailGoogle:EmailBase    10     {    11     12         protected override bool CheckEmailAddress()    13         {    14             Console.WriteLine("Checking Email Address : GoogleEmail");    15             return true;    16         }    17         protected override bool ValidateMessage()    18         {    19             Console.WriteLine("Validating Email Message : GoogleEmail");    20             return true;    21         }    22     23     24         protected override bool SendMail()    25         {    26             Console.WriteLine("Semding Email : GoogleEmail");    27             return true;    28         }    29     30     31     }    32 }    33   Program.cs      1 using System;     2 using System.Collections.Generic;     3 using System.Linq;     4 using System.Text;     5 using System.Threading.Tasks;     6      7 namespace TemplateMethod     8 {     9     class Program    10     {    11         static void Main(string[] args)    12         {    13             Console.WriteLine("Please choose an Email Account to send an Email:");    14             Console.WriteLine("Choose 1 for Google");    15             Console.WriteLine("Choose 2 for Yahoo");    16             string choice = Console.ReadLine();    17     18             if (choice == "1")    19             {    20                 EmailBase email = new EmailGoogle(); // Rather than newing it up here, you may use a factory to do so.    21                 email.SendEmail();    22     23             }    24             if (choice == "2")    25             {    26                 EmailBase email = new EmailYahoo(); // Rather than newing it up here, you may use a factory to do so.    27                 email.SendEmail();    28             }    29         }    30     }    31 }    32    Final Words: It's very obvious that why the Template Method Pattern is a popular pattern, everything at last revolves around Algorithms and if you are clear with the steps involved it makes real sense to delegate the duty of implementing the step's functionality to the sub classes. Normal 0 false false false EN-US X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin-top:0in; mso-para-margin-right:0in; mso-para-margin-bottom:8.0pt; mso-para-margin-left:0in; line-height:107%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi; mso-font-kerning:1.0pt; mso-ligatures:standard;}

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• Oracle Developer Day, Poland, 2012

  - by Geertjan

  Oracle Developer Day took place in Poland today. Oracle's Gregor Rayman did the keynote, where NetBeans was positioned, yet again, as Oracle's IDE for the Java Platform, via the JavaFX Roadmap: Well, it's not so clear from my pic above, but NetBeans is closely tied to the JavaFX Roadmap, as well as the JDK Roadmap too. Then the tracks started, one of which was the Java Track (the other two tracks were on ADF/WebLogic and SOA/BPM/BAM), where among other things I demonstrated the Java EE 6 Platform via tools in NetBeans IDE at some length. The room could hardly have been fuller, chairs had to be brought in and people were standing along the walls. The above pic shows the session being set up, with the room full of developers ready to hear about Java EE 6. I also did a session on pluggable Java desktop development (i.e., NetBeans Platform) and on "What's New in NetBeans IDE 7.1?", while Martin Grebac had a session on Java EE Web Services. Some of the many questions asked during the day that I thought were interesting: Is there localization support for the @Pattern annotation? I.e., what if I want to display the error message in Polish, what do I do? Is there filtering/sorting support for the DataTable component in JSF? Why is there no visual editor for ejb-jar.xml, in the same way that there is for web.xml? "Would be handy if there were to be a JSR for IDE Keyboard Shortcuts." (Two different people asked this question, separately, without knowing about each other. The second didn't know about the Eclipse and IntelliJ keyboard shortcut support in NetBeans IDE and was happy when I told them about it.) Wouldn't it be cool if, on start up, or during installation, there'd be a question: "Are you migrating from Eclipse/IntelliJ?" Then, if "yes", reset the keyboard shortcuts to match the IDE they're coming from.Is there a way in NetBeans to find subclasses of a class? "Would be cool if HTML or JSF files could be visualized in the same way as JavaFX and Swing classes." I.e., Visual Debugger for web developers. I had a great day and am looking at the Oracle Developer Day that will be held in Cluj, Romania, on Friday.

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• How do you handle objects that need custom behavior, and need to exist as an entity in the database?

  - by Scott Whitlock

  For a simple example, assume your application sends out notifications to users when various events happen. So in the database I might have the following tables: TABLE Event EventId uniqueidentifier EventName varchar TABLE User UserId uniqueidentifier Name varchar TABLE EventSubscription EventUserId EventId UserId The events themselves are generated by the program. So there are hard-coded points in the application where an event instance is generated, and it needs to notify all the subscribed users. So, the application itself doesn't edit the Event table, except during initial installation, and during an update where a new Event might be created. At some point, when an event is generated, the application needs to lookup the Event and get a list of Users. What's the best way to link the event in the source code to the event in the database? Option 1: Store the EventName in the program as a fixed constant, and look it up by name. Option 2: Store the EventId in the program as a static Guid, and look it up by ID. Extra Credit In other similar circumstances I may want to include custom behavior with the event type. That is, I'll want subclasses of my Event entity class with different behaviors, and when I lookup an event, I want it to return an instance of my subclass. For instance: class Event { public Guid Id { get; } public Guid EventName { get; } public ReadOnlyCollection<EventSubscription> EventSubscriptions { get; } public void NotifySubscribers() { foreach(var eventSubscription in EventSubscriptions) { eventSubscription.Notify(); } this.OnSubscribersNotified(); } public virtual void OnSubscribersNotified() {} } class WakingEvent : Event { private readonly IWaker waker; public WakingEvent(IWaker waker) { if(waker == null) throw new ArgumentNullException("waker"); this.waker = waker; } public override void OnSubscribersNotified() { this.waker.Wake(); base.OnSubscribersNotified(); } } So, that means I need to map WakingEvent to whatever key I'm using to look it up in the database. Let's say that's the EventId. Where do I store this relationship? Does it go in the event repository class? Should the WakingEvent know declare its own ID in a static member or method? ...and then, is this all backwards? If all events have a subclass, then instead of retrieving events by ID, should I be asking my repository for the WakingEvent like this: public T GetEvent<T>() where T : Event { ... // what goes here? ... } I can't be the first one to tackle this. What's the best practice?

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• What are the differences between abstract classes, interfaces, and when to use them

  - by user66662

  Recently I have started to wrap my head around OOP, and I am now to the point where the more I read about the differences between Abstract classes and Interfaces the more confused I become. So far, neither can be instantiated. Interfaces are more or less structural blueprints that determine the skeleton and abstracts are different by being able to partially develop code. I would like to learn more about these through my specific situation. Here is a link to my first question if you would like a little more background information: What is a good design model for my new class? Here are two classes I created: class Ad { $title; $description $price; function get_data($website){ } function validate_price(){ } } class calendar_event { $title; $description $start_date; function get_data($website){ //guts } function validate_dates(){ //guts } } So, as you can see these classes are almost identical. Not shown here, but there are other functions, like get_zip(), save_to_database() that are common across my classes. I have also added other classes Cars and Pets which have all the common methods and of course properties specific to those objects (mileage, weight, for example). Now I have violated the DRY principle and I am managing and changing the same code across multiple files. I intend on having more classes like boats, horses, or whatever. So is this where I would use an interface or abstract class? From what I understand about abstract classes I would use a super class as a template with all of the common elements built into the abstract class, and then add only the items specifically needed in future classes. For example: abstract class content { $title; $description function get_data($website){ } function common_function2() { } function common_function3() { } } class calendar_event extends content { $start_date; function validate_dates(){ } } Or would I use an interface and, because these are so similar, create a structure that each of the subclasses are forced to use for integrity reasons, and leave it up to the end developer who fleshes out that class to be responsible for each of the details of even the common functions. my thinking there is that some 'common' functions may need to be tweaked in the future for the needs of their specific class. Despite all that above, if you believe I am misunderstanding the what and why of abstracts and interfaces altogether, by all means let a valid answer to be stop thinking in this direction and suggest the proper way to move forward! Thanks!

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• How to refactor my design, if it seems to require multiple inheritance?

  - by Omega

  Recently I made a question about Java classes implementing methods from two sources (kinda like multiple inheritance). However, it was pointed out that this sort of need may be a sign of a design flaw. Hence, it is probably better to address my current design rather than trying to simulate multiple inheritance. Before tackling the actual problem, some background info about a particular mechanic in this framework: It is a simple game development framework. Several components allocate some memory (like pixel data), and it is necessary to get rid of it as soon as you don't need it. Sprites are an example of this. Anyway, I decided to implement something ala Manual-Reference-Counting from Objective-C. Certain classes, like Sprites, contain an internal counter, which is increased when you call retain(), and decreased on release(). Thus the Resource abstract class was created. Any subclass of this will obtain the retain() and release() implementations for free. When its count hits 0 (nobody is using this class), it will call the destroy() method. The subclass needs only to implement destroy(). This is because I don't want to rely on the Garbage Collector to get rid of unused pixel data. Game objects are all subclasses of the Node class - which is the main construction block, as it provides info such as position, size, rotation, etc. See, two classes are used often in my game. Sprites and Labels. Ah... but wait. Sprites contain pixel data, remember? And as such, they need to extend Resource. But this, of course, can't be done. Sprites ARE nodes, hence they must subclass Node. But heck, they are resources too. Why not making Resource an interface? Because I'd have to re-implement retain() and release(). I am avoiding this in virtue of not writing the same code over and over (remember that there are multiple classes that need this memory-management system). Why not composition? Because I'd still have to implement methods in Sprite (and similar classes) that essentially call the methods of Resource. I'd still be writing the same code over and over! What is your advice in this situation, then?

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• Hidden exceptions

  - by user12617285

  Occasionally you may find yourself in a Java application environment where exceptions in your code are being caught by the application framework and either silently swallowed or converted into a generic exception. Either way, the potentially useful details of your original exception are inaccessible. Wouldn't it be nice if there was a VM option that showed the stack trace for every exception thrown, whether or not it's caught? In fact, HotSpot includes such an option: -XX:+TraceExceptions. However, this option is only available in a debug build of HotSpot (search globals.hpp for TraceExceptions). And based on a quick skim of the HotSpot source code, this option only prints the exception class and message. A more useful capability would be to have the complete stack trace printed as well as the code location catching the exception. This is what the various TraceException* options in in Maxine do (and more). That said, there is a way to achieve a limited version of the same thing with a stock standard JVM. It involves the use of the -Xbootclasspath/p non-standard option. The trick is to modify the source of java.lang.Exception by inserting the following: private static final boolean logging = System.getProperty("TraceExceptions") != null; private void log() { if (logging && sun.misc.VM.isBooted()) { printStackTrace(); } } Then every constructor simply needs to be modified to call log() just before returning: public Exception(String message) { super(message); log(); } public Exception(String message, Throwable cause) { super(message, cause); log(); } // etc... You now need to compile the modified Exception.java source and prepend the resulting class to the boot class path as well as add -DTraceExceptions to your java command line. Here's a console session showing these steps: % mkdir boot % javac -d boot Exception.java % java -DTraceExceptions -Xbootclasspath/p:boot -cp com.oracle.max.vm/bin test.output.HelloWorld java.util.zip.ZipException: error in opening zip file at java.util.zip.ZipFile.open(Native Method) at java.util.zip.ZipFile.(ZipFile.java:127) at java.util.jar.JarFile.(JarFile.java:135) at java.util.jar.JarFile.(JarFile.java:72) at sun.misc.URLClassPath$JarLoader.getJarFile(URLClassPath.java:646) at sun.misc.URLClassPath$JarLoader.access$600(URLClassPath.java:540) at sun.misc.URLClassPath$JarLoader$1.run(URLClassPath.java:607) at java.security.AccessController.doPrivileged(Native Method) at sun.misc.URLClassPath$JarLoader.ensureOpen(URLClassPath.java:599) at sun.misc.URLClassPath$JarLoader.(URLClassPath.java:583) at sun.misc.URLClassPath$3.run(URLClassPath.java:333) at java.security.AccessController.doPrivileged(Native Method) at sun.misc.URLClassPath.getLoader(URLClassPath.java:322) at sun.misc.URLClassPath.getLoader(URLClassPath.java:299) at sun.misc.URLClassPath.getResource(URLClassPath.java:168) at java.net.URLClassLoader$1.run(URLClassLoader.java:194) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:190) at sun.misc.Launcher$ExtClassLoader.findClass(Launcher.java:229) at java.lang.ClassLoader.loadClass(ClassLoader.java:306) at java.lang.ClassLoader.loadClass(ClassLoader.java:295) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301) at java.lang.ClassLoader.loadClass(ClassLoader.java:247) java.security.PrivilegedActionException at java.security.AccessController.doPrivileged(Native Method) at sun.misc.URLClassPath$JarLoader.ensureOpen(URLClassPath.java:599) at sun.misc.URLClassPath$JarLoader.(URLClassPath.java:583) at sun.misc.URLClassPath$3.run(URLClassPath.java:333) at java.security.AccessController.doPrivileged(Native Method) at sun.misc.URLClassPath.getLoader(URLClassPath.java:322) ... It's worth pointing out that this is not as useful as direct VM support for tracing exceptions. It has (at least) the following limitations: The trace is shown for every exception, whether it is thrown or not. It only applies to subclasses of java.lang.Exception as there appears to be bootstrap issues when the modification is applied to Throwable.java. It does not show you where the exception was caught. It involves overriding a class in rt.jar, something should never be done in a non-development environment.

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• maintaining a growing, diverse codebase with continuous integration

  - by Nate

  I am in need of some help with philosophy and design of a continuous integration setup. Our current CI setup uses buildbot. When I started out designing it, I inherited (well, not strictly, as I was involved in its design a year earlier) a bespoke CI builder that was tailored to run the entire build at once, overnight. After a while, we decided that this was insufficient, and started exploring different CI frameworks, eventually choosing buildbot. One of my goals in transitioning to buildbot (besides getting to enjoy all the whiz-bang extras) was to overcome some of the inadequacies of our bespoke nightly builder. Humor me for a moment, and let me explain what I have inherited. The codebase for my company is almost 150 unique c++ Windows applications, each of which has dependencies on one or more of a dozen internal libraries (and many on 3rd party libraries as well). Some of these libraries are interdependent, and have depending applications that (while they have nothing to do with each other) have to be built with the same build of that library. Half of these applications and libraries are considered "legacy" and unportable, and must be built with several distinct configurations of the IBM compiler (for which I have written unique subclasses of Compile), and the other half are built with visual studio. The code for each compiler is stored in two separate Visual SourceSafe repositories (which I am simply handling using a bunch of ShellCommands, as there is no support for VSS). Our original nightly builder simply took down the source for everything, and built stuff in a certain order. There was no way to build only a single application, or pick a revision, or to group things. It would launched virtual machines to build a number of the applications. It wasn't very robust, it wasn't distributable. It wasn't terribly extensible. I wanted to be able to overcame all of these limitations in buildbot. The way I did this originally was to create entries for each of the applications we wanted to build (all 150ish of them), then create triggered schedulers that could build various applications as groups, and then subsume those groups under an overall nightly build scheduler. These could run on dedicated slaves (no more virtual machine chicanery), and if I wanted I could simply add new slaves. Now, if we want to do a full build out of schedule, it's one click, but we can also build just one application should we so desire. There are four weaknesses of this approach, however. One is our source tree's complex web of dependencies. In order to simplify config maintenace, all builders are generated from a large dictionary. The dependencies are retrieved and built in a not-terribly robust fashion (namely, keying off of certain things in my build-target dictionary). The second is that each build has between 15 and 21 build steps, which is hard to browse and look at in the web interface, and since there are around 150 columns, takes forever to load (think from 30 seconds to multiple minutes). Thirdly, we no longer have autodiscovery of build targets (although, as much as one of my coworkers harps on me about this, I don't see what it got us in the first place). Finally, aformentioned coworker likes to constantly bring up the fact that we can no longer perform a full build on our local machine (though I never saw what that got us, either, considering that it took three times as long as the distributed build; I think he is just paranoically phobic of ever breaking the build). Now, moving to new development, we are starting to use g++ and subversion (not porting the old repository, mind you - just for the new stuff). Also, we are starting to do more unit testing ("more" might give the wrong picture... it's more like any), and integration testing (using python). I'm having a hard time figuring out how to fit these into my existing configuration. So, where have I gone wrong philosophically here? How can I best proceed forward (with buildbot - it's the only piece of the puzzle I have license to work on) so that my configuration is actually maintainable? How do I address some of my design's weaknesses? What really works in terms of CI strategies for large, (possibly over-)complex codebases?

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• Need to override drawrect if your UIView is merely a container?

  - by Greg Maletic

  According to Apple's docs, "Subclasses need not override -[UIView drawRect:] if the subclass is a container for other views." I have a custom UIView subclass that is indeed merely a container for other views. Yet the contained views aren't getting drawn. Here's the pertinent code that sets up the custom UIView subclass: - (id)initWithFrame:(CGRect)frame { if ((self = [super initWithFrame:frame])) { // Consists of both an "on" light and an "off" light. We flick between the two depending upon our state. self.onLight = [[[LoyaltyCardNumberView alloc] initWithFrame:frame] autorelease]; self.onLight.backgroundColor = [UIColor clearColor]; self.onLight.on = YES; [self addSubview:self.onLight]; self.offLight = [[[LoyaltyCardNumberView alloc] initWithFrame:frame] autorelease]; self.offLight.backgroundColor = [UIColor clearColor]; self.offLight.on = NO; [self addSubview:self.offLight]; self.on = NO; } return self; } When I run the code that displays this custom UIView, nothing shows up. But when I add a drawRect method... - (void)drawRect:(CGRect)rect { [self.onLight drawRect:rect]; [self.offLight drawRect:rect]; } ...the subviews display. (Clearly, this isn't the right way to be doing this, not only because it's contrary to what the docs say, but because it -always- displays both subviews, completely ignoring some other code in my UIView that sets the hidden property of one of the views, it ignores the z-ordering, etc.) Anyway, the main question: why don't my subviews display when I'm not overriding drawRect:? Thanks!

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• Guice and JSF 2

  - by digitaljoel

  I'm trying to use Guice to inject properties of a JSF managed bean. This is all running on Google App Engine (which may or may not be important) I've followed the instructions here: http://code.google.com/docreader/#p=google-guice&s=google-guice&t=GoogleAppEngine One problem is in the first step. I can't subclass the Servlet module and setup my servlet mappings there because Faces is handled by the javax.faces.webapp.FacesServlet which subclasses Servlet, not HttpServlet. So, I tried leaving my servlet configuration in the web.xml file and simply instantiating a new ServletModel() along with my business module when creating the injector in the context listener described in the second step. Having done all that, along with the web.xml configuration, my managed bean isn't getting any properties injected. The method is as follows @ManagedBean @ViewScoped public class ViewTables implements Serializable { private DataService<Table> service; @Inject public void setService( DataService<Table> service ) { this.service = service; } public List<Table> getTables() { return service.getAll(); } } So, I'm wondering if there is a trick to get Guice injecting into a JSF managed bean? I obviously can't use the constructor injection because JSF needs a no-arg constructor to create the bean.

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• Rails: Single Table Inheritance and models subdirectories

  - by Chris

  I have a card-game application which makes use of Single Table Inheritance. I have a class Card, and a database table cards with column type, and a number of subclasses of Card (including class Foo < Card and class Bar < Card, for the sake of argument). As it happens, Foo is a card from the original printing of the game, which Bar is a card from an expansion. In an attempt to rationalise my models, I have created a directory structure like so: app/ + models/ + card.rb + base_game/ + foo.rb + expansion/ + bar.rb And modified environment.rb to contain: Rails::Initializer.run do |config| config.load_paths += Dir["#{RAILS_ROOT}/app/models/**"] end However, when my reads a card from the database, Rails throws the following exception: ActiveRecord::SubclassNotFound (The single-table inheritance mechanism failed to locate the subclass: 'Foo'. This error is raised because the column 'type' is reserved for storing the class in case of inheritance. Please rename this column if you didn't intend it to be used for storing the inheritance class or overwrite Card.inheritance_column to use another column for that information.) Is it possible to make this work, or am I doomed to a flat directory structure?

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