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• When writing a game, should you make objects/enemies/etc. have unique ID numbers?

  - by SLC

  I have recently encountered some issues with merely passing references to objects/enemies in a game I am making, and am wondering if I am using the wrong approach. The main issue I have is disposing of enemies and objects, when other enemies or players may still have links to them. For example, if you have a Rabbit, and a Wolf, the Wolf may have selected the Rabbit to be its target. What I am doing, is the wolf has a GameObject Target = null; and when it decides it is hungry, the Target becomes the Rabbit. If the Rabbit then dies, such as another wolf killing it, it cannot be removed from the game properly because this wolf still has a reference to it. In addition, if you are using a decoupled approach, the rabbit could hit by lightning, reducing its health to below zero. When it next updates itself, it realises it has died, and is removed from the game... but there is no way to update everything that is interested in it. If you gave every enemy a unique ID, you could simply use references to that instead, and use a central lookup class that handled it. If the monster died, the lookup class could remove it from its own index, and subsequently anything trying to access it would be informed that it's dead, and then they could act accordingly. Any thoughts on this?

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• Proper way to set class variables

  - by ensnare

  I'm writing a class to insert users into a database, and before I get too far in, I just want to make sure that my OO approach is clean: class User(object): def setName(self,name): #Do sanity checks on name self._name = name def setPassword(self,password): #Check password length > 6 characters #Encrypt to md5 self._password = password def commit(self): #Commit to database >>u = User() >>u.setName('Jason Martinez') >>u.setPassword('linebreak') >>u.commit() Is this the right approach? Should I declare class variables up top? Should I use a _ in front of all the class variables to make them private? Thanks for helping out.

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• Limit the number of service calls in a RESTful application

  - by Slavo

  Imagine some kind of a banking application, with a screen to create accounts. Each Account has a Currency and a Bank as a property, Currency being a separate class, as well as Bank. The code might look something like this: public class Account { public Currency Currency { get; set; } public Bank Bank { get; set; } } public class Currency { public string Code { get; set; } public string Name { get; set; } } public class Bank { public string Name { get; set; } public string Country { get; set; } } According to the REST design principles, each resource in the application should have its own service, and each service should have methods that map nicely to the HTTP verbs. So in our case, we have an AccountService, CurrencyService and BankService. In the screen for creating an account, we have some UI to select the bank from a list of banks, and to select a currency from a list of currencies. Imagine it is a web application, and those lists are dropdowns. This means that one dropdown is populated from the CurrencyService and one from the BankService. What this means is that when we open the screen for creating an account, we need to make two service calls to two different services. If that screen is not by itself on a page, there might be more service calls from the same page, impacting the performance. Is this normal in such an application? If not, how can it be avoided? How can the design be modified without going away from REST?

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• Suggestions for Single-Page Web Application Design?

  - by DaveDev

  My view is that unless you need to change the basic structure of the user interface, you should not have to reload the page at all for any user interactions. I'd like to approach my next ASP.NET MVC project with this in mind. Can anyone suggest any principles, patterns or practices* I should consider? Excellent book, btw. Still trying to wrap my head around some of the concepts though. I thought a question like this would help link the theory to a practical design. Thanks

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• Generalization arrows

  - by atch

  Do generalization arrows in class diagram has to be strictly open or is there a margin of tolerance on style of this arrows?

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• Object database for website

  - by Damian

  I was planning to use db4o for a website. It's a microblog site with small posts and comments developed in java. The thing is I contacted db4o support asking if db4o would be suitable for a website, and they answered me that only for websites with low concurrency. That means with few requests? So, now I think db4o will not be a good choice. Do you know if there is any object database for java suitable for a website?

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• Invoking WCF service from Javascript

  - by KhanS

  I have a asp.net web application, and have some java script code in it. While calling the service I am getting the exception Service1 is undefined. Below is my code. Service: namespace WebApplication2 { // NOTE: You can use the "Rename" command on the "Refactor" menu to change the interface name "IService1" in both code and config file together. [ServiceContract(Namespace="WCFServices")] public interface IService1 { [OperationContract] string HelloWorld(); } } Implementation namespace WebApplication2 { // NOTE: You can use the "Rename" command on the "Refactor" menu to change the class name "Service1" in code, svc and config file together. [ServiceBehavior(IncludeExceptionDetailInFaults = true)] [AspNetCompatibilityRequirements(RequirementsMode = AspNetCompatibilityRequirementsMode.Allowed)] public class Service1 : IService1 { public string HelloWorld() { return "Hello world from service"; } } } ASPX page: <asp:Content ID="BodyContent" runat="server" ContentPlaceHolderID="MainContent"> <asp:ScriptManager ID="QNAScriptManager" runat="server"> <Services> <asp:ServiceReference Path="~/Service1.svc" /> </Services> <Scripts> <asp:ScriptReference Path="~/Scripts/Questions.js" /> </Scripts> </asp:ScriptManager> </asp:Content> Java Script var ServiceProxy; function pageLoad() { ServiceProxy = new Service1(); ServiceProxy.set_defaultSucceededCallback(SucceededCallback); } function GetString() { ServiceProxy.HelloWorld(); } function SucceededCallback(result, userContext, methodName) { var RsltElem = document.getElementById("Results"); RsltElem.innerHTML = result + " from " + methodName + "."; alert("Msg received from service"); }

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• Class model for a many-to-many relationship, where relationship has attributes

  - by Greg

  Hi, What would the basic C# code look like to model a many-to-many relationship, where the relationship itself has attributes? And also in this case the many-to-many was referential. So a possible database model for this might look like the following (just to give an example of what I'm talking about) Nodes ID Name Description Relationships Parent_ID Child_ID Relationships_Type

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• ASIHTTPRequest code design

  - by nico

  I'm using ASIHTTPRequest to communicate with the server asynchronously. It works great, but I'm doing requests in different controllers and now duplicated methods are in all those controllers. What is the best way to abstract that code (requests) in a single class, so I can easily re-use the code, so I can keep the controllers more simple. I can put it in a singleton (or in the app delegate), but I don't think that's a good approach. Or maybe make my own protocol for it with delegate callback. Any advice on a good design approach would be helpful. Thanks.

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• Implementation of a general-purpose object structure (property bag)

  - by Thomas Wanner

  We need to implement some general-purpose object structure, much like an object in dynamic languages, that would give us a possibility of creating the whole object graph on-the-fly. This class has to be serializable and somehow user friendly. So far we have made some experiments with class derived from Dictionary<string, object> using the dot notation path to store properties and collections in the object tree. We have also find an article that implements something similar, but it doesn't seem to fit completely into our picture either. Do you know about some good implementations / libraries that deal with a similar problem or do you have any (non-trivial) ideas that could help us with our own implementation ? Also, I probably have to say that we are using .NET 3.5, so we can't take advantage of the new features in .NET 4.0 like dynamic type etc. (as far as I know it's also not possible to use any subset of it in .NET 3.5 solution).

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• How to structure a Genetic Algorithm class hierarchy?

  - by MahlerFive

  I'm doing some work with Genetic Algorithms and want to write my own GA classes. Since a GA can have different ways of doing selection, mutation, cross-over, generating an initial population, calculating fitness, and terminating the algorithm, I need a way to plug in different combinations of these. My initial approach was to have an abstract class that had all of these methods defined as pure virtual, and any concrete class would have to implement them. If I want to try out two GAs that are the same but with different cross-over methods for example, I would have to make an abstract class that inherits from GeneticAlgorithm and implements all the methods except the cross-over method, then two concrete classes that inherit from this class and only implement the cross-over method. The downside to this is that every time I want to swap out a method or two to try out something new I have to make one or more new classes. Is there another approach that might apply better to this problem?

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• Adding functionality to any TextReader

  - by strager

  I have a Location class which represents a location somewhere in a stream. (The class isn't coupled to any specific stream.) The location information will be used to match tokens to location in the input in my parser, to allow for nicer error reporting to the user. I want to add location tracking to a TextReader instance. This way, while reading tokens, I can grab the location (which is updated by the TextReader as data is read) and give it to the token during the tokenization process. I am looking for a good approach on accomplishing this goal. I have come up with several designs. Manual location tracking Every time I need to read from the TextReader, I call AdvanceString on the Location object of the tokenizer with the data read. Advantages Very simple. No class bloat. No need to rewrite the TextReader methods. Disadvantages Couples location tracking logic to tokenization process. Easy to forget to track something (though unit testing helps with this). Bloats existing code. Plain TextReader wrapper Create a LocatedTextReaderWrapper class which surrounds each method call, tracking a Location property. Example: public class LocatedTextReaderWrapper : TextReader { private TextReader source; public Location Location { get; set; } public LocatedTextReaderWrapper(TextReader source) : this(source, new Location()) { } public LocatedTextReaderWrapper(TextReader source, Location location) { this.Location = location; this.source = source; } public override int Read(char[] buffer, int index, int count) { int ret = this.source.Read(buffer, index, count); if(ret >= 0) { this.location.AdvanceString(string.Concat(buffer.Skip(index).Take(count))); } return ret; } // etc. } Advantages Tokenization doesn't know about Location tracking. Disadvantages User needs to create and dispose a LocatedTextReaderWrapper instance, in addition to their TextReader instance. Doesn't allow different types of tracking or different location trackers to be added without layers of wrappers. Event-based TextReader wrapper Like LocatedTextReaderWrapper, but decouples it from the Location object raising an event whenever data is read. Advantages Can be reused for other types of tracking. Tokenization doesn't know about Location tracking or other tracking. Can have multiple, independent Location objects (or other methods of tracking) tracking at once. Disadvantages Requires boilerplate code to enable location tracking. User needs to create and dispose the wrapper instance, in addition to their TextReader instance. Aspect-orientated approach Use AOP to perform like the event-based wrapper approach. Advantages Can be reused for other types of tracking. Tokenization doesn't know about Location tracking or other tracking. No need to rewrite the TextReader methods. Disadvantages Requires external dependencies, which I want to avoid. I am looking for the best approach in my situation. I would like to: Not bloat the tokenizer methods with location tracking. Not require heavy initialization in user code. Not have any/much boilerplate/duplicated code. (Perhaps) not couple the TextReader with the Location class. Any insight into this problem and possible solutions or adjustments are welcome. Thanks! (For those who want a specific question: What is the best way to wrap the functionality of a TextReader?) I have implemented the "Plain TextReader wrapper" and "Event-based TextReader wrapper" approaches and am displeased with both, for reasons mentioned in their disadvantages.

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• Relay WCF Service

  - by Matt Ruwe

  This is more of an architectural and security question than anything else. I'm trying to determine if a suggested architecture is necessary. Let me explain my configuration. We have a standard DMZ established that essentially has two firewalls. One that's external facing and the other that connects to the internal LAN. The following describes where each application tier is currently running. Outside the firewall: Silverlight Application In the DMZ: WCF Service (Business Logic & Data Access Layer) Inside the LAN: Database I'm receiving input that the architecture is not correct. Specifically, it has been suggested that because "a web server is easily hacked" that we should place a relay server inside the DMZ that communicates with another WCF service inside the LAN which will then communicate with the database. The external firewall is currently configured to only allow port 443 (https) to the WCF service. The internal firewall is configured to allow SQL connections from the WCF service in the DMZ. Ignoring the obvious performance implications, I don't see the security benefit either. I'm going to reserve my judgement of this suggestion to avoid polluting the answers with my bias. Any input is appreciated. Thanks, Matt

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• Attribute References in Python

  - by Jeune

  I do Java programming and recently started learning Python via the official documentation. I see that we can dynamically add data attributes to an instance object unlike in Java: class House: pass my_house = House() my_house.number = 40 my_house.rooms = 8 my_house.garden = 1 My question is, in what situations is this feature used? What are the advantages and disadvantages compared to the way it is done in Java?

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• XAML Binding to complex value objects

  - by Gus

  I have a complex value object class that has 1) a number or read-only properties; 2) a private constructor; and 3) a number of static singleton instance properties [so the properties of a ComplexValueObject never change and an individual value is instantiated once in the application's lifecycle]. public class ComplexValueClass { /* A number of read only properties */ private readonly string _propertyOne; public string PropertyOne { get { return _propertyOne; } } private readonly string _propertyTwo; public string PropertyTwo { get { return _propertyTwo; } } /* a private constructor */ private ComplexValueClass(string propertyOne, string propertyTwo) { _propertyOne = propertyOne; _propertyTwo = PropertyTwo; } /* a number of singleton instances */ private static ComplexValueClass _complexValueObjectOne; public static ComplexValueClass ComplexValueObjectOne { get { if (_complexValueObjectOne == null) { _complexValueObjectOne = new ComplexValueClass("string one", "string two"); } return _complexValueObjectOne; } } private static ComplexValueClass _complexValueObjectTwo; public static ComplexValueClass ComplexValueObjectTwo { get { if (_complexValueObjectTwo == null) { _complexValueObjectTwo = new ComplexValueClass("string three", "string four"); } return _complexValueObjectTwo; } } } I have a data context class that looks something like this: public class DataContextClass : INotifyPropertyChanged { private ComplexValueClass _complexValueClass; public ComplexValueClass ComplexValueObject { get { return _complexValueClass; } set { _complexValueClass = value; PropertyChanged(this, new PropertyChangedEventArgs("ComplexValueObject")); } } } I would like to write a XAML binding statement to a property on my complex value object that updates the UI whenever the entire complex value object changes. What is the best and/or most concise way of doing this? I have something like: <Object Value="{Binding ComplexValueObject.PropertyOne}" /> but the UI does not update when ComplexValueObject as a whole changes.

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• Are ORM's counterproductive to OO design?

  - by Jeremiah

  In OOD, design of an object is said to be characterized by its identity and behavior. Having used OR/M's in the past, the primary purpose, in my opinion, revolves around the ability to store/retrieve data. That is to say, OR/M objects are not design by behavior, but rather data (i.e. database tables). Case and point: Many OR/M tools come with a point-to-a-database-table-and-click-object-generator. If objects are no longer characterized by behavior this will, in my opinion, muddy the identity and responsibility of the objects. Subsequently, if objects are not defined by a responsibility this could lend a hand to having tightly coupled classes and overall poor design. Furthermore, I would think that in an application setting, you would be heading towards scalability issues. So, my question is, do you think that ORM's are counterproductive to OO design? Perhaps the underlying question would be whether or not they are counterproductive to application development.

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• Is the design notion of layers contrived?

  - by Bruce

  Hi all I'm reading through Eric Evans' awesome work, Domain-Driven Design. However, I can't help feeling that the 'layers' model is contrived. To expand on that statement, it seems as if it tries to shoe-horn various concepts into a specific, neat model, that of layers talking to each other. It seems to me that the layers model is too simplified to actually capture the way that (good) software works. To expand further: Evans says: "Partition a complex program into layers. Develop a design within each layer that is cohesive and that depends only on the layers below. Follow standard architectural patterns to provide loose coupling to the layers above." Maybe I'm misunderstanding what 'depends' means, but as far as I can see, it can either mean a) Class X (in the UI for example) has a reference to a concrete class Y (in the main application) or b) Class X has a reference to a class Y-ish object providing class Y-ish services (ie a reference held as an interface). If it means (a), then this is clearly a bad thing, since it defeats re-using the UI as a front-end to some other application that provides Y-ish functionality. But if it means (b), then how is the UI any more dependent on the application, than the application is dependent on the UI? Both are decoupled from each other as much as they can be while still talking to each other. Evans' layer model of dependencies going one way seems too neat. First, isn't it more accurate to say that each area of the design provides a module that is pretty much an island to itself, and that ideally all communication is through interfaces, in a contract-driven/responsibility-driven paradigm? (ie, the 'dependency only on lower layers' is contrived). Likewise with the domain layer talking to the database - the domain layer is as decoupled (through DAO etc) from the database as the database is from the domain layer. Neither is dependent on the other, both can be swapped out. Second, the idea of a conceptual straight line (as in from one layer to the next) is artificial - isn't there more a network of intercommunicating but separate modules, including external services, utility services and so on, branching off at different angles? Thanks all - hoping that your responses can clarify my understanding on this..

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• looking for automated modeling tool for ASP.Net class diagramming

  - by alchemical

  I'm walking into a project with 500+ classes, and am wondering if anyone has had good experiences with automated modeling tools that can import from ASP.Net /C#? It would be a bonus if I could get an automated model based on all the objects called to completely load a single ASP.Net page, with relationships indicating which objects are calling out to which other ones, etc. Thanks for sharing your thoughts or recomendations.

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• Accessing the Private Constructor

  - by harigm

  I am java developer, went for an interview. I have been asked a question about the Private constructor 1) Can I access a Private Constructor of a Class and Instantiate the class. I was thinking and gave the answer directly--- "NO" But its wrong, can any one help Why NO? and How we can achieve this

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• Wrappers/law of demeter seems to be an anti-pattern...

  - by Robert Fraser

  I've been reading up on this "Law of Demeter" thing, and it (and pure "wrapper" classes in general) seem to generally be anti patterns. Consider an implementation class: class Foo { void doSomething() { /* whatever */ } } Now consider two different implementations of another class: class Bar1 { private static Foo _foo = new Foo(); public static Foo getFoo() { return _foo; } } class Bar2 { private static Foo _foo = new Foo(); public static void doSomething() { _foo.doSomething(); } } And the ways to call said methods: callingMethod() { Bar1.getFoo().doSomething(); // Version 1 Bar2.doSomething(); // Version 2 } At first blush, version 1 seems a bit simpler, and follows the "rule of Demeter", hide Foo's implementation, etc, etc. But this ties any changes in Foo to Bar. For example, if a parameter is added to doSomething, then we have: class Foo { void doSomething(int x) { /* whatever */ } } class Bar1 { private static Foo _foo = new Foo(); public static Foo getFoo() { return _foo; } } class Bar2 { private static Foo _foo = new Foo(); public static void doSomething(int x) { _foo.doSomething(x); } } callingMethod() { Bar1.getFoo().doSomething(5); // Version 1 Bar2.doSomething(5); // Version 2 } In both versions, Foo and callingMethod need to be changed, but in Version 2, Bar also needs to be changed. Can someone explain the advantage of having a wrapper/facade (with the exception of adapters or wrapping an external API or exposing an internal one).

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• USE case to Class Diagram - How do I?

  - by 01010011

  Hi, I would like your guidance on how to create classes and their relationships (generalization, association, aggregation and composition) accurately from my USE case diagram (please see below). I am trying to create this class diagram so I can use it to create a simple online PHP application that allows the user to register an account, login and logout, and store, search and retrieve data from a MySQL database. Are my classes correct? Or should I create more classes? And if so, what classes are missing? What relationships should I use when connecting the register, login, logout, search_database and add_to_database to the users? I'm new to design patterns and UML class diagrams but from my understanding, the association relationship relates one object with another object; the aggregation relationship is a special kind of association that allows "a part" to belong to more than one "whole" (e.g. a credit card and its PIN - the PIN class can also be used in a debit card class); and a composition relationship is a special form of aggregation that allows each part to belong to only one whole at a time. I feel like I have left out some classes or something because I just can't seem to find the relationships from my understanding of relationships. Any assistance will be really appreciated. Thanks in advance. USE CASE DIAGRAM CLASS DIAGRAM

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• Collaboration Diagrams: how to represent setting a variable's and attribute's value to a specified v

  - by devoured elysium

  Let's assume I have a class called MyClass with an attribute called MyAttribute and a method called MyMethod(). Inside that method I'd like to have a variable called MyVariable. I'd like to set the value of MyVariable to "MyVariable" and MyAttribute to "MyAttribute" inside the call to MyMethod(). How can I do this in a Collaboration Diagram? I can't find any info of this kind on the internet and the book I'm studying from (Applying UML and Patterns) is very vague in the details. Thanks

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• Example with Visitor Pattern

  - by devoured elysium

  public class Song { public string Genre { get; protected set; } public string Name { get; protected set; } public string Band { get; protected set; } public Song(string name, string band, string genre) { Name = name; Genre = genre; Band = band; } } public interface IMusicVisistor { void Visit(List<Song> items); } public class MusicLibrary { List<Song> _songs = new List<Song> { ...songs ... }; public void Accept(IMusicVisitor visitor) { visitor.Visit(_songs); } } and now here's one Visitor I made: public class RockMusicVisitor : IMusicVisitor { public List<Song> Songs { get; protected set; } public void Visit(List<Song> items) { Songs = items.Where(x => x.Genre == "Rock").ToList(); } } Why is this any better than just putting a public property Songs and then letting any kind of class do with it anything that it wants to? This example comes from this post.

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• Steps in creating a web service using Axis2 - The client code

  - by zengr

  I am trying to create a web service, my tools of trade are: ** Axis2, Eclipse, Tomcat, Ant ** I need to create a web service from Code, i.e. Write a basic java class which will have the methods to be declared in the WSDL. Then use java2WSDL.sh to create my WSDL. So, is this approach correct: Write my Java class with actual business logic package packageNamel; public class Hello{ public void World(String name) { SOP("Hello" + name); } } Now, when I pass this Hello.java to java2WSDL.sh, this will give me the WSDL. Finally, I will write the services.xml file, and create the Hello.aar with following dir structure: Hello.aar packageName Hello.class META-INF services.xml MANIFEST.MF Hello.WSDL Now, I assume, my service will be deployed when I put the aar in tomcat1/webapps/axis2/WEB-INF/services But, here comes my problem, HOW DO I ACCESS THE METHOD World(String name)???!!, i.e. I am clueless about the client code! Please enlighten me on making a very basic web service and calling the method. The above described 3 steps might be wrong. It's a community wiki, feel free to edit. Thanks

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• Abstract class in Java

  - by keyur

  What is an "abstract class" in Java?

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