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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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  • Web Safe Area (optimal resolution) for web app design

    - by M.A.X
    I'm in the process of designing a new web app and I'm wondering for what 'web safe area' should I optimize the app layout and design. I did some investigation and thinking on my own but wanted to share this to see what the general opinion is. Here is what I found: Optimal Display Resolution: w3schools web stats seems to be the most referenced source (however they state that these are results from their site and is biased towards tech savvy users) http://www.w3counter.com/globalstats.php (aggregate data from something like 15,000 different sites that use their tracking services) StatCounter Global Stats Display Resolution (Stats are based on aggregate data collected by StatCounter on a sample exceeding 15 billion pageviews per month collected from across the StatCounter network of more than 3 million websites) NetMarketShare Screen Resolutions (marketshare.hitslink.com) (a web analytics consulting firm, they get data from browsers of site visitors to their on-demand network of live stats customers. The data is compiled from approximately 160 million visitors per month) Display Resolution Summary: There is a bit of variation between the above sources but in general as of Jan 2011 looks like 1024x768 is about 20%, while ~85% have a higher resolution of at least 1280x768 (1280x800 is the most common of these with 15-20% of total web, depending on the source; 1280x1024 and 1366x768 follow behind with 9-14% of the share). My guess would be that the higher resolution values will be even more common if we filter on North America, and even higher if we filter on N.American corporate users (unfortunately I couldn't find any free geographically filtered statistics). Another point to note is that the 1024x768 desktop user population is likely lower than the aforementioned 20%, seeing as the iPad (1024x768 native display) is likely propping up those number. My recommendation would be to optimize around the 1280x768 constraint (*note: 1280x768 is actually a relatively rare resolution, but I think it's a valid constraint range considering that 1366x768 is relatively common and 1280 is the most common horizontal resolution). Browser + OS Constraints: To further add to the constraints we have to subtract the space taken up by the browser (assuming IE, which is the most space consuming) and the OS (assuming WinXP-Win7): Win7 has the biggest taskbar footprint at a height of 40px (XP's and Vista's is 30px) The default IE8 view uses up 25px at the bottom of the screen with the status bar and a further 120px at the top of the screen with the windows title bar and the browser UI (assuming the default 'favorites' toolbar is present, it would instead be 91px without the favorites toolbar). Assuming no scrollbar, we also loose a total of 4px horizontally for the window outline. This means that we are left with 583px of vertical space and 1276px of horizontal. In other words, a Web Safe Area of 1276 x 583 Is this a correct line of thinking? I tried to Google some design best practices but most still talk about designing around 1024x768 which seems to be quickly disappearing. Any help on this would be greatly appreciated! Thanks.

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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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  • 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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  • 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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  • 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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  • Is it worthwhile to implement observer pattern in PHP?

    - by Extrakun
    I have been meaning to make use of design pattern in PHP, such as the observer pattern, but that I have to recreate the observers' relationship each time the page is loaded pains me. As references are saved as a new concrete objects in session, there is no way to preserve relationships between subscribers and their observers unless you use a GUID or some other properties to form a lookup, and store that property instead. With the cost of recreating the relationships each time a page is loaded, is it worthwhile to use design patterns such as observers in PHP, compared to having a clean design? Any real-world experience to share?

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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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  • Java - how to design your own type?

    - by Walter White
    Hi all, Is it possible to design your own Java Type, say an extensible enum? For instance, I have user roles that a certain module uses and then a sub-package provides additional roles. What would be involved on the JDK side of things? Walter

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  • inner class within Interface

    - by harigm
    is that possible to create a inner class within an interface? If yes, why do we create like that? Anyways we are not going to create any interface objects? Do they help in any Development process?

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  • Clear all class variables between instances

    - by ensnare
    This is probably a stupid question, but what's the best way to clear class variables between instances? I know I could reset each variable individually in the constructor; but is there a way to do this in bulk? Or am I doing something totally wrong that requires a different approach? Thanks for helping ... class User(): def __init__(self): #RESET ALL CLASS VARIABLES def commit(self): #Commit variables to database >>u = User() >>u.name = 'Jason' >>u.email = '[email protected]' >>u.commit() So that each time User is called the variables are fresh. Thanks.

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  • iphone: caching and updating xml fields

    - by pJosh
    Thanks for your help. Here I have another question. I get the data through XMLParsing, now I want to store it in iphone's cache, and the XML Fields are updates every 12 hours.how can i check that XML Fields are change or not? and how can I store the data in iphone's cache memory so that evry it does not has to interact with web. Can anybody please help me???

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  • Personal project in Java

    - by Chuck
    My first project in java is going to be a program (eventually I have to create a GUI interface but for now CLI would do) to keep track of my books (something similar to what libraries have only a simpler). I need to be able to insert, update, remove, show all books, update, search(by name or author or date). For the design I was thinking one main class Library which will have all of the above as methods that connect to the db and retrieve the data. Is this approach ok? I realize it's simple but it's my first real project and I would appreciate a little feedback. Also, is it too soon to consider reading up on design patterns and database design ?

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  • Create a Python User() class that both creates new users and modifies existing users

    - by ensnare
    I'm trying to figure out the best way to create a class that can modify and create new users all in one. This is what I'm thinking: class User(object): def __init__(self,user_id): if user_id == -1 self.new_user = True else: self.new_user = False #fetch all records from db about user_id self._populateUser() def commit(self): if self.new_user: #Do INSERTs else: #Do UPDATEs def delete(self): if self.new_user == False: return False #Delete user code here def _populate(self): #Query self.user_id from database and #set all instance variables, e.g. #self.name = row['name'] def getFullName(self): return self.name #Create a new user >>u = User() >>u.name = 'Jason Martinez' >>u.password = 'linebreak' >>u.commit() >>print u.getFullName() >>Jason Martinez #Update existing user >>u = User(43) >>u.name = 'New Name Here' >>u.commit() >>print u.getFullName() >>New Name Here Is this a logical and clean way to do this? Is there a better way? Thanks.

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  • read access violation error

    - by user293569
    class Node{ private: string name; Node** adjacent; int adjNum; public: Node(); Node(string, int adj_num); Node(const Node &); bool addAdjacent(const Node &); Node** getAdjacents(); string getName(); ~Node(); }; bool Node::addAdjacent(const Node &anode){ Node** temp; temp= new Node*[adjNum+1]; for(int i=0;i<adjNum+1;i++) temp[i]=adjacent[i]; temp[adjNum]=const_cast<Node *>(&anode); delete[] adjacent; adjacent=new Node*[adjNum+1]; adjacent=temp; delete[] temp; adjNum++; return true; } int main() { Node node1("A",0); Node node2("B",0); node1.getName(); node1.addAdjacent(node2); system("PAUSE"); return 0; } when the program comes to this part: for(int i=0;i<adjNum+1;i++) temp[i]=adjacent[i]; it says Access violation reading location 0xcccccccc. The class must allocate the memory fore adjacent, but I think it didn't how can I solve this problem?

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  • Tinyxml Multi Task

    - by shaimagz
    I have a single xml file and every new thread of the program (BHO) is using the same Tinyxml file. every time a new window is open in the program, it runs this code: const char * xmlFileName = "C:\\browsarityXml.xml"; TiXmlDocument doc(xmlFileName); doc.LoadFile(); //some new lines in the xml.. and than save: doc.SaveFile(xmlFileName); The problem is that after the first window is adding new data to the xml and saves it, the next window can't add to it. although the next one can read the data in the xml, it can't write to it. I thought about two possibilities to make it work, but I don't know how to implement them: Destroy the doc object when I'm done with it. Some function in Tinyxml library to unload the file. Any help or better understanding of the problem will be great. Thanks.

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  • Aren't Information Expert / Tell Don't Ask at odds with Single Responsibility Principle?

    - by moffdub
    It is probably just me, which is why I'm asking the question. Information Expert, Tell Don't Ask, and SRP are often mentioned together as best practices. But I think they are at odds. Here is what I'm talking about: Code that favors SRP but violates Tell Don't Ask, Info Expert: Customer bob = ...; // TransferObjectFactory has to use Customer's accessors to do its work, // violates Tell Don't Ask CustomerDTO dto = TransferObjectFactory.createFrom(bob); Code that favors Tell Don't Ask / Info Expert but violates SRP: Customer bob = ...; // Now Customer is doing more than just representing the domain concept of Customer, // violates SRP CustomerDTO dto = bob.toDTO(); If they are indeed at odds, that's a vindication of my OCD. Otherwise, please fill me in on how these practices can co-exist peacefully. Thank you. Edit: someone wants a definition of the terms - Information Expert: objects that have the data needed for the operation should host the operation Tell Don't Ask: don't ask objects for data in order to do work; tell the objects to do the work Single Responsibility Principle: each object should have a narrowly defined responsibility

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  • Fluid Design bugs in ie7

    - by Qwibble
    Hey guys, I've created a dummy layout for my latest design, but when I resize the window in ie7 to check that the min-width works, it kicks the content area to below the sidebar, whereas in all other browsers (including ie6) it behaves exactly as it should do. Demo Link Can anyone see what the problem is that's causing this random couple extra pixels that kick it off?

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