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• Why is quicksort better than other sorting algorithms in practice?

  - by Raphael

  This is a repost of a question on cs.SE by Janoma. Full credits and spoils to him or cs.SE. In a standard algorithms course we are taught that quicksort is O(n log n) on average and O(n²) in the worst case. At the same time, other sorting algorithms are studied which are O(n log n) in the worst case (like mergesort and heapsort), and even linear time in the best case (like bubblesort) but with some additional needs of memory. After a quick glance at some more running times it is natural to say that quicksort should not be as efficient as others. Also, consider that students learn in basic programming courses that recursion is not really good in general because it could use too much memory, etc. Therefore (and even though this is not a real argument), this gives the idea that quicksort might not be really good because it is a recursive algorithm. Why, then, does quicksort outperform other sorting algorithms in practice? Does it have to do with the structure of real-world data? Does it have to do with the way memory works in computers? I know that some memories are way faster than others, but I don't know if that's the real reason for this counter-intuitive performance (when compared to theoretical estimates).

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• Use a SQL Database for a Desktop Game

  - by sharethis

  Developing a Game Engine I am planning a computer game and its engine. There will be a 3 dimensional world with first person view and it will be single player for now. The programming language is C++ and it uses OpenGL. Data Centered Design Decision My design decision is to use a data centered architecture where there is a global event manager and a global data manager. There are many components like physics, input, sound, renderer, ai, ... Each component can trigger and listen to events. Moreover, each component can read, edit, create and remove data. The question is about the data manager. Whether to Use a Relational Database Should I use a SQL Database, e.g. SQLite or MySQL, to store the game data? This contains virtually all game content like items, characters, inventories, ... Except of meshes and textures which are even more performance related, so I will keep them in memory. Is a SQL database fast enough to use it for realtime reading and writing game informations, like the position of a moving character? I also need to care about cross-platform compatibility. Aside from keeping everything in memory, what alternatives do I have? Advantages Would Be The advantages of using a relational database like MySQL would be the data orientated structure which allows fast computation. I would not need objects for representing entities. I could easily query data of objects near the player needed for rendering. And I don't have to take care about data of objects far away. Moreover there would be no need for savegames since the hole game state is saved in the database. Last but not least, expanding the game to an online game would be relative easy because there already is a place where the hole game state is stored.

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• Java single Array best choice for accessing pixels for manipulation?

  - by Petrol

  I am just watching this tutorial https://www.youtube.com/watch?v=HwUnMy_pR6A and the guy (who seems to be pretty competent) is using a single array to store and access the pixels of his to-be-rendered image. I was wondering if this really is the best way to do this. The alternative of Multi-Array does have one pointer more, but Arrays do have an O(1) for accessing each index and calculating the index in a single array seems to take one addition and one multiplication operation per pixel. And if Multi-Arrays really are bad, can't you use something with Hashing to avoid those addition and multiplication operations? EDIT: here is his code... public class Screen { private int width, height; public int[] pixels; public Screen(int width, int height) { this.width = width; this.height = height; // creating array the size of one index/int for every pixel // single array has better performance than multi-array pixels = new int[width * height]; } public void render() { for (int y = 0; y < height; y++) { for (int x = 0; x < width; x++) { pixels[x + y * width] = 0xff00ff; } } } }

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• Design suggestions needed to create a MathBuilder framework

  - by Darf Zon

  Let explain what I'm trying to create. I'm creating a framework, the idea is to provide base classes to generate a math problem. Why do I need this framework? Because at first time, I realized when I create a new math problem I always do the same steps. Configuration settings such range numbers. For example if I'm developing multiplications, in beginner level only generate the first number between 2-5 or in advanced level, the first number will be between 6- 9, for example. Generate problem method. All the time I need to invoke a method like this to generate the problem. This one receives the configuration settings and generate the number according to them. And generate the object with the respective data. Validate the problem. Sometimes the problem generated is not valid. For example, supposed I'm creating fractions in most simplified, if I receive 2/4, the program should detect that this is not valid and must generate another like this one, 1/4. Load the view. All of them, have a custom view (please watch below the images). All of the problems must know how to CHECK if the user result is correct. All of this problems has answers. Some of them just require one answer, anothers may require more than one, so I guess a way to maintain flexibility to the developer has all the answers he wanna used. At the beginning I started using PRISM. Generate modules for each math problem was the idea and load it in the main system. I guess are the most important things of this idea. Let me showing some problems which I create in a WPF standalone program. Here I have a math problem about areas. When I generate the problem a set to the view the object and it draw it. In beginner level, I set in the configuration settings that just load square types. But in advance level, can load triangles and squares randomly. In this another, generate a binary problem like addition, subtraction, multiplication or division. Above just generate a single problem. The idea of this is to show a test o quiz, I mean get a worksheet (this I call as a collection of problems) where the user can answer it. I hope gets the idea with my ugly drawing. How to load this math problems? As I said above, I started using PRISM, and each module contains a math problem kind. This is a snapshot of my first demo. Below show the modules loaded, and center the respective configurations or levels. Until momment, I have no idea to start creating this software. I just know that I need a question | problem class, response class, user class. But I get lost about what properties should have to contain in it. Please give a little hand of this framework. I put much effort on this question, so if any isn't clear, let me know to clarify it.

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• Starting to create a MathBuilder framework, help to start creating the design

  - by Darf Zon

  Let explain what I'm trying to create. I'm creating a framework, the idea is to provide base classes to generate a math problem. Why do I need this framework? Because at first time, I realized when I create a new math problem I always do the same steps. Configuration settings such range numbers. For example if I'm developing multiplications, in beginner level only generate the first number between 2-5 or in advanced level, the first number will be between 6- 9, for example. Generate problem method. All the time I need to invoke a method like this to generate the problem. This one receives the configuration settings and generate the number according to them. And generate the object with the respective data. Validate the problem. Sometimes the problem generated is not valid. For example, supposed I'm creating fractions in most simplified, if I receive 2/4, the program should detect that this is not valid and must generate another like this one, 1/4. Load the view. All of them, have a custom view (please watch below the images). All of the problems must know how to CHECK if the user result is correct. All of this problems has answers. Some of them just require one answer, anothers may require more than one, so I guess a way to maintain flexibility to the developer has all the answers he wanna used. At the beginning I started using PRISM. Generate modules for each math problem was the idea and load it in the main system. I guess are the most important things of this idea. Let me showing some problems which I create in a WPF standalone program. Here I have a math problem about areas. When I generate the problem a set to the view the object and it draw it. In beginner level, I set in the configuration settings that just load square types. But in advance level, can load triangles and squares randomly. In this another, generate a binary problem like addition, subtraction, multiplication or division. Above just generate a single problem. The idea of this is to show a test o quiz, I mean get a worksheet (this I call as a collection of problems) where the user can answer it. I hope gets the idea with my ugly drawing. How to load this math problems? As I said above, I started using PRISM, and each module contains a math problem kind. This is a snapshot of my first demo. Below show the modules loaded, and center the respective configurations or levels. Until momment, I have no idea to start creating this software. I just know that I need a question | problem class, response class, user class. But I get lost about what properties should have to contain in it. Please give a little hand of this framework. I put much effort on this question, so if any isn't clear, let me know to clarify it.

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• Project structure: where to put business logic

  - by Mister Smith

  First of all, I'm not asking where does business logic belong. This has been asked before and most answers I've read agree in that it belongs in the model: Where to put business logic in MVC design? How much business logic should be allowed to exist in the controller layer? How accurate is "Business logic should be in a service, not in a model"? Why put the business logic in the model? What happens when I have multiple types of storage? However people disagree in the way this logic should be distributed across classes. There seem to exist three major currents of thought: Fat model with business logic inside entity classes. Anemic model and business logic in "Service" classes. It depends. I find all of them problematic. The first option is what most Fowlerites stick to. The problem with a fat model is that sometimes a business logic funtion is not only related to a class, and instead uses a bunch of other classes. If, for example, we are developing a web store, there should be a function that calcs an order's total. We could think of putting this function inside the Order class, but what actually happens is that the logic needs to use different classes, not only data contained in the Order class, but also in the User class, the Session class, and maybe the Tax class, Country class, or Giftcard, Payment, etc. Some of these classes could be composed inside the Order class, but some others not. Sorry if the example is not very good, but I hope you understand what I mean. Putting such a function inside the Order class would break the single responsibility principle, adding unnecesary dependences. The business logic would be scattered across entity classes, making it hard to find. The second option is the one I usually follow, but after many projects I'm still in doubt about how to name the class or classes holding the business logic. In my company we usually develop apps with offline capabilities. The user is able to perform entire transactions offline, so all validation and business rules should be implemented in the client, and then there's usually a background thread that syncs with the server. So we usually have the following classes/packages in every project: Data model (DTOs) Data Access Layer (Persistence) Web Services layer (Usually one class per WS, and one method per WS method). Now for the business logic, what is the standard approach? A single class holding all the logic? Multiple classes? (if so, what criteria is used to distribute the logic across them?). And how should we name them? FooManager? FooService? (I know the last one is common, but in our case it is bad naming because the WS layer usually has classes named FooWebService). The third option is probably the right one, but it is also devoid of any useful info. To sum up: I don't like the first approach, but I accept that I might have been unable to fully understand the Zen of it. So if you advocate for fat models as the only and universal solution you are welcome to post links explaining how to do it the right way. I'd like to know what is the standard design and naming conventions for the second approach in OO languages. Class names and package structure, in particular. It would also be helpful too if you could include links to Open Source projects showing how it is done. Thanks in advance.

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• Why is there no service-oriented language?

  - by Wolfgang

  Edit: To avoid further confusion: I am not talking about web services and such. I am talking about structuring applications internally, it's not about how computers communicate. It's about programming languages, compilers and how the imperative programming paradigm is extended. Original: In the imperative programming field, we saw two paradigms in the past 20 years (or more): object-oriented (OO), and service-oriented (SO) aka. component-based (CB). Both paradigms extend the imperative programming paradigm by introducing their own notion of modules. OO calls them objects (and classes) and lets them encapsulates both data (fields) and procedures (methods) together. SO, in contrast, separates data (records, beans, ...) from code (components, services). However, only OO has programming languages which natively support its paradigm: Smalltalk, C++, Java and all other JVM-compatibles, C# and all other .NET-compatibles, Python etc. SO has no such native language. It only comes into existence on top of procedural languages or OO languages: COM/DCOM (binary, C, C++), CORBA, EJB, Spring, Guice (all Java), ... These SO frameworks clearly suffer from the missing native language support of their concepts. They start using OO classes to represent services and records. This leads to designs where there is a clear distinction between classes that have methods only (services) and those that have fields only (records). Inheritance between services or records is then simulated by inheritance of classes. Technically, its not kept so strictly but in general programmers are adviced to make classes to play only one of the two roles. They use additional, external languages to represent the missing parts: IDL's, XML configurations, Annotations in Java code, or even embedded DSL like in Guice. This is especially needed, but not limited to, since the composition of services is not part of the service code itself. In OO, objects create other objects so there is no need for such facilities but for SO there is because services don't instantiate or configure other services. They establish an inner-platform effect on top of OO (early EJB, CORBA) where the programmer has to write all the code that is needed to "drive" SO. Classes represent only a part of the nature of a service and lots of classes have to be written to form a service together. All that boiler plate is necessary because there is no SO compiler which would do it for the programmer. This is just like some people did it in C for OO when there was no C++. You just pass the record which holds the data of the object as a first parameter to the procedure which is the method. In a OO language this parameter is implicit and the compiler produces all the code that we need for virtual functions etc. For SO, this is clearly missing. Especially the newer frameworks extensively use AOP or introspection to add the missing parts to a OO language. This doesn't bring the necessary language expressiveness but avoids the boiler platform code described in the previous point. Some frameworks use code generation to produce the boiler plate code. Configuration files in XML or annotations in OO code is the source of information for this. Not all of the phenomena that I mentioned above can be attributed to SO but I hope it clearly shows that there is a need for a SO language. Since this paradigm is so popular: why isn't there one? Or maybe there are some academic ones but at least the industry doesn't use one.

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• What are the disadvantages of self-encapsulation?

  - by Dave Jarvis

  Background Tony Hoare's billion dollar mistake was the invention of null. Subsequently, a lot of code has become riddled with null pointer exceptions (segfaults) when software developers try to use (dereference) uninitialized variables. In 1989, Wirfs-Brock and Wikerson wrote: Direct references to variables severely limit the ability of programmers to re?ne existing classes. The programming conventions described here structure the use of variables to promote reusable designs. We encourage users of all object-oriented languages to follow these conventions. Additionally, we strongly urge designers of object-oriented languages to consider the effects of unrestricted variable references on reusability. Problem A lot of software, especially in Java, but likely in C# and C++, often uses the following pattern: public class SomeClass { private String someAttribute; public SomeClass() { this.someAttribute = "Some Value"; } public void someMethod() { if( this.someAttribute.equals( "Some Value" ) ) { // do something... } } public void setAttribute( String s ) { this.someAttribute = s; } public String getAttribute() { return this.someAttribute; } } Sometimes a band-aid solution is used by checking for null throughout the code base: public void someMethod() { assert this.someAttribute != null; if( this.someAttribute.equals( "Some Value" ) ) { // do something... } } public void anotherMethod() { assert this.someAttribute != null; if( this.someAttribute.equals( "Some Default Value" ) ) { // do something... } } The band-aid does not always avoid the null pointer problem: a race condition exists. The race condition is mitigated using: public void anotherMethod() { String someAttribute = this.someAttribute; assert someAttribute != null; if( someAttribute.equals( "Some Default Value" ) ) { // do something... } } Yet that requires two statements (assignment to local copy and check for null) every time a class-scoped variable is used to ensure it is valid. Self-Encapsulation Ken Auer's Reusability Through Self-Encapsulation (Pattern Languages of Program Design, Addison Wesley, New York, pp. 505-516, 1994) advocated self-encapsulation combined with lazy initialization. The result, in Java, would resemble: public class SomeClass { private String someAttribute; public SomeClass() { setAttribute( "Some Value" ); } public void someMethod() { if( getAttribute().equals( "Some Value" ) ) { // do something... } } public void setAttribute( String s ) { this.someAttribute = s; } public String getAttribute() { String someAttribute = this.someAttribute; if( someAttribute == null ) { setAttribute( createDefaultValue() ); } return someAttribute; } protected String createDefaultValue() { return "Some Default Value"; } } All duplicate checks for null are superfluous: getAttribute() ensures the value is never null at a single location within the containing class. Efficiency arguments should be fairly moot -- modern compilers and virtual machines can inline the code when possible. As long as variables are never referenced directly, this also allows for proper application of the Open-Closed Principle. Question What are the disadvantages of self-encapsulation, if any? (Ideally, I would like to see references to studies that contrast the robustness of similarly complex systems that use and don't use self-encapsulation, as this strikes me as a fairly straightforward testable hypothesis.)

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• Is my class structure good enough?

  - by Rivten

  So I wanted to try out this challenge on reddit which is mostly about how you structure your data the best you can. I decided to challenge my C++ skills. Here's how I planned this. First, there's the Game class. It deals with time and is the only class main has access to. A game has a Forest. For now, this class does not have a lot of things, only a size and a Factory. Will be put in better use when it will come to SDL-stuff I guess A Factory is the thing that deals with the Game Objects (a.k.a. Trees, Lumberjack and Bears). It has a vector of all GameObjects and a queue of Events which will be managed at the end of one month. A GameObject is an abstract class which can be updated and which can notify the Event Listener The EventListener is a class which handles all the Events of a simulation. It can recieve events from a Game Object and notify the Factory if needed, the latter will manage correctly the event. So, the Tree, Lumberjack and Bear classes all inherits from GameObject. And Sapling and Elder Tree inherits from Tree. Finally, an Event is defined by an event_type enumeration (LUMBERJACK_MAWED, SAPPLING_EVOLUTION, ...) and an event_protagonists union (a GameObject or a pair of GameObject (who killed who ?)). I was quite happy at first with this because it seems quite logic and flexible. But I ended up questionning this structure. Here's why : I dislike the fact that a GameObject need to know about the Factory. Indeed, when a Bear moves somewhere, it needs to know if there's a Lumberjack ! Or it is the Factory which handles places and objects. It would be great if a GameObject could only interact with the EventListener... or maybe it's not that much of a big deal. Wouldn't it be better if I separate the Factory in three vectors ? One for each kind of GameObject. The idea would be to optimize research. If I'm looking do delete a dead lumberjack, I would only have to look in one shorter vector rather than a very long vector. Another problem arises when I want to know if there is any particular object in a given case because I have to look for all the gameObjects and see if they are at the given case. I would tend to think that the other idea would be to use a matrix but then the issue would be that I would have empty cases (and therefore unused space). I don't really know if Sapling and Elder Tree should inherit from Tree. Indeed, a Sapling is a Tree but what about its evolution ? Should I just delete the sapling and say to the factory to create a new Tree at the exact same place ? It doesn't seem natural to me to do so. How could I improve this ? Is the design of an Event quite good ? I've never used unions before in C++ but I didn't have any other ideas about what to use. Well, I hope I have been clear enough. Thank you for taking the time to help me !

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• Series of abstract classes and NHibernate

  - by Chris Cowdery-Corvan

  Hello, and first off thanks for your time to look at this. For a research project I'm working on, I have a somewhat complex design (which I've been given) to persist to a database via NHibernate. Here's an example of the class hierarchy: TransitStrategy, TransportationCompany and TransportationLocation are all abstract classes. The XML configuration I have is presently: <?xml version="1.0" encoding="utf-8" ?> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="Vacationizer" namespace="Vacationizer.Domain.Transit"> <class name="TransitStrategy"> <id name="TransitStrategyId"> <generator class="guid" /> </id> <property name="Restrictions" /> <joined-subclass name="Flight" table="Flight_TransitStrategy"> <key column="TransitStrategyId" /> <property name="DepartingAirport" /> <property name="ArrivingAirport" /> <property name="Airline" /> <property name="FlightNumber" /> <property name="FlightArrivalTime" /> <property name="FlightDepartureTime" /> </joined-subclass> <joined-subclass name="RentalCar" table="RentalCar_TransitStrategy"> <key column="TransitStrategyId" /> <property name="RentalCarBranch" /> <property name="CarMake" /> <property name="CarModel" /> <property name="CarYear" /> <property name="CarColor" /> <property name="RentalBegins" /> <property name="RentalEnds" /> </joined-subclass> </class> <?xml version="1.0" encoding="utf-8" ?> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="Vacationizer" namespace="Vacationizer.Domain.Transit"> <class name="TransportationCompany"> <id name="TransportationCompanyId"> <generator class="guid" /> </id> <property name="Name" /> <property name="Reviews" /> <property name="Website" /> <property name="Photo" /> <joined-subclass name="Airline" table="Airline_TransportationCompany"> <key column="TransportationLocationId" /> </joined-subclass> <joined-subclass name="RentalCarAgency" table="RentalCarAgency_TransportationCompany"> <key column="TransportationLocationId" /> </joined-subclass> </class> <?xml version="1.0" encoding="utf-8" ?> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="Vacationizer" namespace="Vacationizer.Domain.Transit"> <class name="TransportationLocation"> <id name="TransportationLocationId"> <generator class="guid" /> </id> <property name="Name" /> <property name="Image" /> <property name="Geolocation" /> <property name="Reviews" /> <!-- <property name="HoursOpen" />--> <property name="PhoneNumber" /> <property name="FaxNumber" /> <joined-subclass name="Airport" table="Airport_TransportationLocation"> <key column="TransportationLocationId" /> <property name="AirportCode" /> <property name="Website" /> </joined-subclass> <joined-subclass name="RentalCarBranch" table="RentalCarBranch_TransportationLocation"> <key column="TransitStrategyId" /> <property name="Agency" /> </joined-subclass> </class> However, whenever I try to use this schema I get this error/stack trace: ------ Test started: Assembly: Vacationizer.Tests.dll ------ TestCase 'M:Vacationizer.Tests.VacationRepository_Fixture.TestFixtureSetUp' failed: Could not compile the mapping document: Vacationizer.Mappings.TransitStrategy.hbm.xml NHibernate.MappingException: Could not compile the mapping document: Vacationizer.Mappings.TransitStrategy.hbm.xml ---> NHibernate.MappingException: Problem trying to set property type by reflection ---> NHibernate.MappingException: class Vacationizer.Domain.Transit.RentalCar, Vacationizer, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null not found while looking for property: RentalCarBranch ---> NHibernate.PropertyNotFoundException: Could not find a getter for property 'RentalCarBranch' in class 'Vacationizer.Domain.Transit.RentalCar' at NHibernate.Properties.BasicPropertyAccessor.GetGetter(Type type, String propertyName) at NHibernate.Util.ReflectHelper.ReflectedPropertyClass(String className, String name, String accessorName) --- End of inner exception stack trace --- at NHibernate.Util.ReflectHelper.ReflectedPropertyClass(String className, String name, String accessorName) at NHibernate.Mapping.SimpleValue.SetTypeUsingReflection(String className, String propertyName, String accesorName) --- End of inner exception stack trace --- at NHibernate.Mapping.SimpleValue.SetTypeUsingReflection(String className, String propertyName, String accesorName) at NHibernate.Cfg.XmlHbmBinding.ClassBinder.CreateProperty(IValue value, String propertyName, String className, XmlNode subnode, IDictionary`2 inheritedMetas) at NHibernate.Cfg.XmlHbmBinding.ClassBinder.PropertiesFromXML(XmlNode node, PersistentClass model, IDictionary`2 inheritedMetas, UniqueKey uniqueKey, Boolean mutable, Boolean nullable, Boolean naturalId) at NHibernate.Cfg.XmlHbmBinding.JoinedSubclassBinder.HandleJoinedSubclass(PersistentClass model, XmlNode subnode, IDictionary`2 inheritedMetas) at NHibernate.Cfg.XmlHbmBinding.ClassBinder.PropertiesFromXML(XmlNode node, PersistentClass model, IDictionary`2 inheritedMetas, UniqueKey uniqueKey, Boolean mutable, Boolean nullable, Boolean naturalId) at NHibernate.Cfg.XmlHbmBinding.RootClassBinder.Bind(XmlNode node, HbmClass classSchema, IDictionary`2 inheritedMetas) at NHibernate.Cfg.XmlHbmBinding.MappingRootBinder.AddRootClasses(XmlNode parentNode, IDictionary`2 inheritedMetas) at NHibernate.Cfg.XmlHbmBinding.MappingRootBinder.Bind(XmlNode node) at NHibernate.Cfg.Configuration.AddValidatedDocument(NamedXmlDocument doc) --- End of inner exception stack trace --- at NHibernate.Cfg.Configuration.LogAndThrow(Exception exception) at NHibernate.Cfg.Configuration.AddValidatedDocument(NamedXmlDocument doc) at NHibernate.Cfg.Configuration.ProcessMappingsQueue() at NHibernate.Cfg.Configuration.AddDocumentThroughQueue(NamedXmlDocument document) at NHibernate.Cfg.Configuration.AddXmlReader(XmlReader hbmReader, String name) at NHibernate.Cfg.Configuration.AddInputStream(Stream xmlInputStream, String name) at NHibernate.Cfg.Configuration.AddResource(String path, Assembly assembly) at NHibernate.Cfg.Configuration.AddAssembly(Assembly assembly) at NHibernate.Cfg.Configuration.AddAssembly(String assemblyName) at NHibernate.Cfg.Configuration.DoConfigure(IHibernateConfiguration hc) at NHibernate.Cfg.Configuration.Configure() VacationRepository_Fixture.cs(24,0): at Vacationizer.Tests.VacationRepository_Fixture.TestFixtureSetUp() 0 passed, 1 failed, 0 skipped, took 8.38 seconds (Ad hoc). Any ideas on how I can implement this differently? Thanks very much!

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• Object Oriented PHP Best Practices

  - by user270797

  Say I have a class which represents a person, a variable within that class would be $name. Previously, In my scripts I would create an instance of the object then set the name by just using: $object->name = "x"; However, I was told this was not best practice? That I should have a function set_name() or something similar like this: function set_name($name) { $this->name=$name; } is this correct? If in this example I want to insert a new "person" record into the db, how do I pass all the information about the person ie $name, $age, $address, $phone etc to the class in order to insert it, should I do: function set($data) { $this->name= $data['name']; $this->age = $data['age']; etc etc } Then send it an array? Would this be best practice? or could someone please recommend best practice?

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• What is the Relative Performance of Pseudo-Class and Custom Selectors?

  - by James Wiseman

  It's my understanding that, in terms of selector speed, that #ID selectors are fastest, followed by element selectors, and then .class selectors. I have always assumed that pseudo-class selectors and custom selectors (those in the form ':selector') are similar to .class selectors, but I realised that I'm just not sure. I realise that this does depend on the complexity of the code within the pseudo-class/custom selector, so I guess I'd like to know the answer with this excluded as factor. Any help would be appreciated. Thanks.

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• Ever any performance different between Java >> and >>> right shift operators?

  - by Sean Owen

  Is there ever reason to think the (signed) and (unsigned) right bit-shift operators in Java would perform differently? I can't detect any difference on my machine. This is purely an academic question; it's never going to be the bottleneck I'm sure. I know: it's best to write what you mean foremost; use for division by 2, for example. I assume it comes down to which architectures have which operations implemented as an instruction.

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• easiest way to convert virtualbox snapshots to tree view

  - by amir beygi

  HI all My virtual box snapshot view is like this Name: Snapshot 2 (UUID: cb45aef4-54d4-4c4e-ad3e-dd7cccb6103a) Name: s131 (UUID: 8ec30c82-7796-4e51-8161-979f1b95fb0f) Name: s131 (UUID: 42066f33-969b-41f3-a779-7f6e2c45ea2c) Name: s131 (UUID: d71b9bc5-b862-46b5-ae4d-f88d3dd9756d) Name: s131 (UUID: 681896a9-7e61-4b5a-90bc-cb1bd785c6fc) Name: s131 (UUID: d7bf8593-d218-442d-b23b-4ee16e74087d) Name: s131 (UUID: e8b16fd2-7add-4294-b908-34c4e6dc79dc) Name: s131 (UUID: 57c3f5d7-d4ed-4a62-a7b8-5594f819e08e) Name: Snapshot 3 (UUID: 4a684149-9dd6-4bb2-baf5-5f590e91a344) Name: Snapshot 4 (UUID: d4cbaa7c-ae78-41e0-9962-46c587a9c667) Name: Snapshot 5 (UUID: 81567b6e-eea9-49a6-b3b8-a07f0be337d8) * and i want to convert this text to a tree like this Name: Snapshot 2 (UUID: cb45aef4-54d4-4c4e-ad3e-dd7cccb6103a) +--Name: s131 (UUID: 8ec30c82-7796-4e51-8161-979f1b95fb0f) +--Name: s131 (UUID: 42066f33-969b-41f3-a779-7f6e2c45ea2c) +--Name: s131 (UUID: d71b9bc5-b862-46b5-ae4d-f88d3dd9756d) +--Name: s131 (UUID: 681896a9-7e61-4b5a-90bc-cb1bd785c6fc) | +--Name: s131 (UUID: d7bf8593-d218-442d-b23b-4ee16e74087d) | +--Name: s131 (UUID: e8b16fd2-7add-4294-b908-34c4e6dc79dc) | +--Name: s131 (UUID: 57c3f5d7-d4ed-4a62-a7b8-5594f819e08e) +--Name: Snapshot 3 (UUID: 4a684149-9dd6-4bb2-baf5-5f590e91a344) +--Name: Snapshot 4 (UUID: d4cbaa7c-ae78-41e0-9962-46c587a9c667) +--Name: Snapshot 5 (UUID: 81567b6e-eea9-49a6-b3b8-a07f0be337d8) * or even an array that contents line number and parent's line number. My environment is linux, programming language is C, and i got this results from this shell command VBoxManage snapshot s2000 showvminfo s|grep Name|grep UUID

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• getting the name of the calling method

  - by zeocrash

  Basically i've got a web service that i'm trying to put some kind of usage logging in. To do this i've created a class with a logging method. I instatiate the class on the service and then call the logging method in each of the web methods. I'm trying to find a way of getting the name of the method that has called the loggong method Public sub tstmethod log_object.log_method end sub in this case the returned name i'm looking for is "tstmethod" Everywhere i've seen has said to either use Dim stackframe As New Diagnostics.StackFrame Return stackframe.GetMethod.Name.ToString Or to use Dim stackframe As New Diagnostics.StackFrame Return stackframe.GetMethod.DeclaringType.FullName which i call inside the logging method getmethod.name.tostring returns the name of the logging method getmethod.declaringtype.fullname returns the name of the logging class no matter what i do i cannot find a way of getting the name of the method that called the logging method in this case "tstmethod"

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• How best to pre-install OR pre-load OR cache Java Script library to optimize performance.

  - by Kabeer

  Hello. I am working for an intranet application. Therefore I have some control on the client machines. The Java Script library I am using is somewhat big in size. I would like to pre-install OR pre-load OR cache the Java Script library on each machine (each browser as well) so that it does not travel for each request. I know that browsers do cache a Java Script library for subsequent requests but I would like the library to be cached once so all subsequent requests, sessions and users. What is the best mechanism to achieve this?

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• How does this code break the Law of Demeter?

  - by Dave Jarvis

  The following code breaks the Law of Demeter: public class Student extends Person { private Grades grades; public Student() { } /** Must never return null; throw an appropriately named exception, instead. */ private synchronized Grades getGrades() throws GradesException { if( this.grades == null ) { this.grades = createGrades(); } return this.grades; } /** Create a new instance of grades for this student. */ protected Grades createGrades() throws GradesException { // Reads the grades from the database, if needed. // return new Grades(); } /** Answers if this student was graded by a teacher with the given name. */ public boolean isTeacher( int year, String name ) throws GradesException, TeacherException { // The method only knows about Teacher instances. // return getTeacher( year ).nameEquals( name ); } private Grades getGradesForYear( int year ) throws GradesException { // The method only knows about Grades instances. // return getGrades().getForYear( year ); } private Teacher getTeacher( int year ) throws GradesException, TeacherException { // This method knows about Grades and Teacher instances. A mistake? // return getGradesForYear( year ).getTeacher(); } } public class Teacher extends Person { public Teacher() { } /** * This method will take into consideration first name, * last name, middle initial, case sensitivity, and * eventually it could answer true to wild cards and * regular expressions. */ public boolean nameEquals( String name ) { return getName().equalsIgnoreCase( name ); } /** Never returns null. */ private synchronized String getName() { if( this.name == null ) { this.name == ""; } return this.name; } } Questions How is the LoD broken? Where is the code breaking the LoD? How should the code be written to uphold the LoD?

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• Can I set a property on an object that is only declared on the instance type, when I don't know the

  - by WilberBeast

  Let me explain. I have a List into which I am adding various ASP.NET controls. I then wish to loop through the list and set a CssClass, however not every Control supports the property CssClass. What I would like to do is test if the underlying instance type supports the CssClass property and set it, but I'm not sure how to do the conversion prior to setting the property since I don't know the type of each Control object. I know that I can use typeof or x.GetType(), but I'm not sure how to use these to convert the controls back to the instance type in order to test for and then set the property. Actually I seem to have solved this, so I thought that I would post the code here for others. foreach (Control c in controlList) { PropertyInfo pi = c.GetType().GetProperty("CssClass"); if (pi != null) pi.SetValue(c, "desired_css_class", null); } I hope that this helps someone else as I has taken me hours to research these 2 lines of code. Cheers Steve

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• Spaceship objects

  - by Jam

  I'm trying to make a program which creates a spaceship and I'm using the status() method to display the ship's name and fuel values. However, it doesn't seem to be working. I think I may have messed something up with the status() method. I'm also trying to make it so that I can change the fuel values, but I don't want to create a new method to do so. I think I've taken a horrible wrong turn somewhere in there. Help please! class Ship(object): def __init__(self, name="Enterprise", fuel=0): self.name=name self.fuel=fuel print "The spaceship", name, "has arrived!" def status(): print "Name: ", self.name print "Fuel level: ", self.fuel status=staticmethod(status) def main(): ship1=Ship(raw_input("What would you like to name this ship?")) fuel_level=raw_input("How much fuel does this ship have?") if fuel_level<0: self.fuel=0 else: self.fuel(fuel_level) ship2=Ship(raw_input("What would you like to name this ship?")) fuel_level2=raw_input("How much fuel does this ship have?") if fuel_level2<0: self.fuel=0 else: self.fuel(fuel_level2) ship3=Ship(raw_input("What would you like to name this ship?")) fuel_level3=raw_input("How much fuel does this ship have?") if fuel_level3<0: self.fuel=0 else: self.fuel(fuel_level3) Ship.status() main() raw_input("Press enter to exit.")

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• How best to pre-install OR pre-load OR cache JavaScript library to optimize performance?

  - by Kabeer

  Hello. I am working for an intranet application. Therefore I have some control on the client machines. The JavaScript library I am using is somewhat big in size. I would like to pre-install OR pre-load OR cache the JavaScript library on each machine (each browser as well) so that it does not travel for each request. I know that browsers do cache a JavaScript library for subsequent requests but I would like the library to be cached once for all subsequent requests, sessions and users. What is the best mechanism to achieve this?

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• Why does Microsoft Windows' performance appear to degrade over time?

  - by Ben Aston

  Windows XP/2k3 and earlier (can't attest to Vista, but suspect it's the same) all appear to become more sluggish over time as applications are installed and uninstalled. This is not a scientifically tested observation, but more of a learned-through-experience piece of wisdom. (I've always suspected the registry as being behind the issue.) Does anyone have any concrete evidence of this degradation occurring, or it just an invalid perception of mine?

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• Adding file of the same name into the same list and unable to update name of the SPFile

  - by BeraCim

  Hi all: I'm having difficulties adding file of the same name in the same list and subsequently updating/changing/modifying the name of a SPFile. Basically, this is what I'm trying to do: string fileName = "something"; // obtained from a loop -- loop omitted here. SPFile file = folder.Files.Add(fileName, otherFile.OpenBinary()); The Add method will generate a runtime exception when it finds another file of the same name in the same list/folder. So I thought of changing the file name later in the process: string newGuid = Guid.NewGuid().ToString(); SPFile file = folder.Files.Add(newGuid, otherFile.OpenBinary()); // some other processing... afterwards, rename the file file.name = fileName; file.Item.Update(); A few minute of googling indicated I need to either move the file around, or update the name field by using ["Name"] instead. I was wondering are there any other better ways to get around this problem? Thanks.

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• How do I name an array key with a key inside the array

  - by Confused

  I have some data, yes, data. This data came from a MySQL query and it will always contain 4 items, always. I want to cache that data in an array table for use later within a web page but I want to keep the keys from the query and separate out each grouping within a multidimensional array. However to save time iterating through the array each time I want to find a given group of data, I want to call the keys of the first array the same as the ID key which is always the first key within each four items. At the minute I'm using this code: function mysql_fetch_full_result_array($result) { $table_result=array(); $r=0; while($row = mysql_fetch_assoc($result)){ $arr_row=array(); $c=0; while ($c < mysql_num_fields($result)) { $col = mysql_fetch_field($result, $c); $arr_row[$col -> name] = $row[$col -> name]; $c++; } $table_result[$r] = $arr_row; $r++; } return $table_result; } I'm currently testing this using 3 unique users, so I'm getting three rows back from the query and the data from this function ends up in the format: [0]=> . . [id] => 1 . . [name] => random name . . [tel] => random tel . . [post] => post code data [1]=> . . [id] => 34 . . [name] => random name . . [tel] => random tel . . [post] => post code data [2]=> . . [id] => 56 . . [name] => random name . . [tel] => random tel . . [post] => post code data So how do I alter the code to instead of the keys [0], [1], [2] give me the output: [1]=> . . [id] => 1 . . [name] => random name . . [tel] => random tel . . [post] => post code data [34]=> . . [id] => 34 . . [name] => random name . . [tel] => random tel . . [post] => post code data [56]=> . . [id] => 56 . . [name] => random name . . [tel] => random tel . . [post] => post code data I don't mind if the main array keys are strings of numbers rather than numbers but I'm a bit stuck, I tried changing the $table_result[$r] = $arr_row; part to read $table_result[$result['id']] = $arr_row; but that just outputs an array of one person. I know I need another loop but I'm struggling to work out how to write it.

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• Why ruby object has two to_s and inspect methods that (looks like) do the same thing?

  - by prosseek

  The p calls inspect, and puts/print calls to_s for representing its object. If I run class Graph def initialize @nodeArray = Array.new @wireArray = Array.new end def to_s # called with print / puts "Graph : #{@nodeArray.size}" end def inspect # called with p "G" end end if __FILE__ == $0 gr = Graph.new p gr print gr puts gr end I get G Graph : 0Graph : 0 Then, why does ruby has two functions do the same thing? What makes the difference between to_s and inspect? And what's the difference between puts/print/p? If I comment out the to_s or inspect function, I get as follows. #<Graph:0x100124b88>#<Graph:0x100124b88>

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• Java: How do you access a sub-object of an object with no "getXXX" method to that sub-object

  - by Daxon

  I'll explain with pictures from Eclipse Debugger I have an Class called "FieldContext", (I can't edit it, it's compiled in the Java OVal API) Within "FieldContext" on the eclipse variable tab are "CompileTimeType" and "field" Q1 Is there a legend for the icons in the variables tab? like what the red box with the "F" means + yellow diamond boxes? Now I want to access the fields inside the "field" object (RedBox) .. preferably "name" But the "FieldContext" does not have a "getField()" method, yet it has a "getCompileTimeType()" method. Q2 So is there anyway to get that field object being a "SerializableField" Class from the "FieldContext"? If eclipse debugger can see/get/edit them then I hope I can do the same in Java.

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