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  • Relationship DAO, Servlet, JSP and POJO

    - by John Hendrik
    I want to implement a JSP, POJO, DAO and Servlet in my J2EE program. However, I don't fully understand how the relationship between these elements should be. Is the following (MVC) setup the right way to do it? Main class creates servlet(controller) Servlet has a DAO defined in its class DAO has a POJO defined in its class Servlet communicates with the view (JSP page) Please give your feedback.

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  • What is the proper name for this design pattern in Python?

    - by James
    In Python, is the proper name for the PersonXXX class below PersonProxy, PersonInterface, etc? import rest class PersonXXX(object): def __init__(self,db_url): self.resource = rest.Resource(db_url) def create(self,person): self.resource.post(person.data()) def get(self): pass def update(self): pass def delete(self): pass class Person(object): def __init__(self,name, age): self.name = name self.age = age def data(self): return dict(name=self.name,age=self.age)

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  • Saving Dragged Dropped items position on postback in asp.net [closed]

    - by Deeptechtons
    Ok i saw many post's on how to serialize the value of dragged items to get hash and they tell how to save them. Now the question is how do i persist the dragged items the next time when user log's in using the has value that i got eg: <ul class="list"> <li id="id_1"> <div class="item ui-corner-all ui-widget ui-widget-content"> </div> </li> <li id="id_2"> <div class="item ui-corner-all ui-widget ui-widget-content"> </div> </li> <li id="id_3"> <div class="item ui-corner-all ui-widget ui-widget-content"> </div> </li> <li id="id_4"> <div class="item ui-corner-all ui-widget"> </div> </li> </ul> which on serialize will give "id[]=1&id[]=2&id[]=3&id[]=4" Now think that i saved it to Sql server database in a single field called SortOrder. Now how do i get the items to these order again ? the code to make these sort is below,without which people didn't know which library i had used to sort and serialize <script type="text/javascript"> $(document).ready(function() { $(".list li").css("cursor", "move"); $(".list").sortable(); }); </script>

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  • Base Pages and Interfaces for ASP.NET Pages

    - by geekrutherford
    For quite a while I have been using the concept of base pages when developing pages in ASP.NET applications. It is a wonderful method for exposing common functions to all of your applications pages and also overriding certain events for various purposes (i.e. dynamic themes).  Recently I found out a new developer will be joining my team. This prompted me to review the applications code for readability and ease of maintenance. I began adding comments through out the code behind for all pages within the application. While doing so I noted that I had used common method names for such things as loading data, configuring controls, applying filters, etc.   Bringing a new developer on board, I wanted to make the transition as seamless as possible while also ensuring they follow existing coding practices we already have in place. While I could have created virtual methods for the common page methods allowing them to overridden, what I really needed was a way to ensure the new developer implemented the same methods for each and every page. Thus I created an interface to force the issue.   Now, every page not only inherits the base page class but also implements an interface. This provides every page not only common functions and overridden page events but also imposes rules for implementing certain common methods :-)   Interface   public interface BasePageInterface { /// Configures page based on users security permissions. void CheckPermissions(); /// Configures Filter Form control for current page.  /// Ensure you have set the FilteredGrid and PageAjaxManager properties of the FilterForm control in PageLoad!!!  void ConfigureFilters(); /// Sets event handlers and default settings for controls on the current page. void ConfigureControls(); /// Exports data bound to grid in selected format. void ExportGridData(ExportFormat fmt); /// Loads data and binds to grid. /// Columns are turned on/off in grid depending on tab selected and users permissions.  void LoadData(); }   Page code-behind class definition:   public partial class MyPage : BasePage, BasePageInterface Note, you could not use an abstract class to accomplish this considering C# does not allow for multiple inheritance.  Nor could the base page class be abstract since it needs to inherit from the System.Web.UI.Page class in order to override page events.

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  • Useful Extension Method for ICloneable

    - by DesigningCode
    In the past, I’ve had to put a type specific clone in each cloneable class, but with extension methods you can write a generic T specific clone class Program { static void Main(string[] args) { var b = new Blah() {X = 1, Y = 2}; var bb = b.Clone(); Console.WriteLine(string.Format("{0} {1}", bb.X, bb.Y)); } } public class Blah : ICloneable { public int X; public int Y; object ICloneable.Clone() { return MemberwiseClone(); } } public static class CloneExtension { public static T Clone<T>(this T o) where T : ICloneable { return (T)o.Clone(); } }

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  • Design for an interface implementation that provides additional functionality

    - by Limbo Exile
    There is a design problem that I came upon while implementing an interface: Let's say there is a Device interface that promises to provide functionalities PerformA() and GetB(). This interface will be implemented for multiple models of a device. What happens if one model has an additional functionality CheckC() which doesn't have equivalents in other implementations? I came up with different solutions, none of which seems to comply with interface design guidelines: To add CheckC() method to the interface and leave one of its implementations empty: interface ISomeDevice { void PerformA(); int GetB(); bool CheckC(); } class DeviceModel1 : ISomeDevice { public void PerformA() { // do stuff } public int GetB() { return 1; } public bool CheckC() { bool res; // assign res a value based on some validation return res; } } class DeviceModel2 : ISomeDevice { public void PerformA() { // do stuff } public int GetB() { return 1; } public bool CheckC() { return true; // without checking anything } } This solution seems incorrect as a class implements an interface without truly implementing all the demanded methods. To leave out CheckC() method from the interface and to use explicit cast in order to call it: interface ISomeDevice { void PerformA(); int GetB(); } class DeviceModel1 : ISomeDevice { public void PerformA() { // do stuff } public int GetB() { return 1; } public bool CheckC() { bool res; // assign res a value based on some validation return res; } } class DeviceModel2 : ISomeDevice { public void PerformA() { // do stuff } public int GetB() { return 1; } } class DeviceManager { private ISomeDevice myDevice; public void ManageDevice(bool newDeviceModel) { myDevice = (newDeviceModel) ? new DeviceModel1() : new DeviceModel2(); myDevice.PerformA(); int b = myDevice.GetB(); if (newDeviceModel) { DeviceModel1 newDevice = myDevice as DeviceModel1; bool c = newDevice.CheckC(); } } } This solution seems to make the interface inconsistent. For the device that supports CheckC(): to add the logic of CheckC() into the logic of another method that is present in the interface. This solution is not always possible. So, what is the correct design to be used in such cases? Maybe creating an interface should be abandoned altogether in favor of another design?

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  • Hosting and consuming WCF services without configuration files

    - by martinsj
    In this post, I'll demonstrate how to configure both the host and the client in code without the need for configuring services i the <system.serviceModel> section of the config-file. In fact, you don't need a  <system.serviceModel> section at all. What you'll do need (and want) sometimes, is the Uri of the service in the configuration file. Configuring the Uri of the the service is actually only needed for the client or when self-hosting, not when hosting in IIS. So, exactly What do we need to configure? The binding type and the binding constraints The metadata behavior Debug behavior You can of course configure even more, and even more if you want to, WCF is after all the king of configuration… As an example I'll be hosting and consuming a service that removes most of the default constraints for WCF-services, using a BasicHttpBinding. Of course, in regards to security, it is probably better to have some constraints on the server, but this is only a demonstration. The ServerConfig class in the code beneath is a static helper class that will be used in the examples. In this post, I’ll be using this helper-class for all configuration, for both the server and the client. In WCF, the  client and the server have both their own WCF-configuration. With this piece of code, they will be sharing the same configuration. 1: public static class ServiceConfig 2: { 3: public static Binding DefaultBinding 4: { 5: get 6: { 7: var binding = new BasicHttpBinding(); 8: Configure(binding); 9: return binding; 10: } 11: } 12:  13: public static void Configure(HttpBindingBase binding) 14: { 15: if (binding == null) 16: { 17: throw new ArgumentException("Argument 'binding' cannot be null. Cannot configure binding."); 18: } 19:  20: binding.SendTimeout = new TimeSpan(0, 0, 30, 0); // 30 minute timeout 21: binding.MaxBufferSize = Int32.MaxValue; 22: binding.MaxBufferPoolSize = 2147483647; 23: binding.MaxReceivedMessageSize = Int32.MaxValue; 24: binding.ReaderQuotas.MaxArrayLength = Int32.MaxValue; 25: binding.ReaderQuotas.MaxBytesPerRead = Int32.MaxValue; 26: binding.ReaderQuotas.MaxDepth = Int32.MaxValue; 27: binding.ReaderQuotas.MaxNameTableCharCount = Int32.MaxValue; 28: binding.ReaderQuotas.MaxStringContentLength = Int32.MaxValue; 29: } 30:  31: public static ServiceMetadataBehavior ServiceMetadataBehavior 32: { 33: get 34: { 35: return new ServiceMetadataBehavior 36: { 37: HttpGetEnabled = true, 38: MetadataExporter = {PolicyVersion = PolicyVersion.Policy15} 39: }; 40: } 41: } 42:  43: public static ServiceDebugBehavior ServiceDebugBehavior 44: { 45: get 46: { 47: var smb = new ServiceDebugBehavior(); 48: Configure(smb); 49: return smb; 50: } 51: } 52:  53:  54: public static void Configure(ServiceDebugBehavior behavior) 55: { 56: if (behavior == null) 57: { 58: throw new ArgumentException("Argument 'behavior' cannot be null. Cannot configure debug behavior."); 59: } 60: 61: behavior.IncludeExceptionDetailInFaults = true; 62: } 63: } Configuring the server There are basically two ways to host a WCF service, in IIS and self-hosting. When hosting a WCF service in a production environment using SOA architecture, you'll be most likely hosting it in IIS. When testing the service in integration tests, it's very handy to be able to self-host services in the unit-tests. In fact, you can share the the WCF configuration for self-hosted services and services hosted in IIS. And that is exactly what you want to do, testing the same configurations for test and production environments.   Configuring when Self-hosting When self-hosting, in order to start the service, you'll have to instantiate the ServiceHost class, configure the  service and open it. 1: // Create the service-host. 2: var host = new ServiceHost(typeof(MyService), endpoint); 3:  4: // Configure the binding 5: host.AddServiceEndpoint(typeof(IMyService), ServiceConfig.DefaultBinding, endpoint); 6:  7: // Configure metadata behavior 8: host.Description.Behaviors.Add(ServiceConfig.ServiceMetadataBehavior); 9:  10: // Configure debgug behavior 11: ServiceConfig.Configure((ServiceDebugBehavior)host.Description.Behaviors[typeof(ServiceDebugBehavior)]); 12: 13: // Start listening to the service 14: host.Open(); 15:  Configuring when hosting in IIS When you create a WCF service application with the wizard in Visual Studio, you'll end up with bits and pieces of code in order to get the service running: Svc-file with codebehind. A interface to the service Web.config In order to get rid of the configuration in the <system.serviceModel> section, which the wizard has generated for us, we must tell the service that we have a factory that will create the service for us. We do this by changing the markup for the svc-file: 1: <%@ ServiceHost Language="C#" Debug="true" Service="Namespace.MyService" Factory="Namespace.ServiceHostFactory" %> The markup tells IIS that we have a factory called ServiceHostFactory for this service. The service factory has a method we can override which will be called when someone asks IIS for the service. There are overloads we can override: 1: System.ServiceModel.ServiceHostBase CreateServiceHost(string constructorString, Uri[] baseAddresses) 2: System.ServiceModel.ServiceHost CreateServiceHost(Type serviceType, Uri[] baseAddresses) 3:  In this example, we'll be using the last one, so our implementation looks like this: 1: public class ServiceHostFactory : System.ServiceModel.Activation.ServiceHostFactory 2: { 3:  4: protected override System.ServiceModel.ServiceHost CreateServiceHost(Type serviceType, Uri[] baseAddresses) 5: { 6: var host = base.CreateServiceHost(serviceType, baseAddresses); 7: host.Description.Behaviors.Add(ServiceConfig.ServiceMetadataBehavior); 8: ServiceConfig.Configure((ServiceDebugBehavior)host.Description.Behaviors[typeof(ServiceDebugBehavior)]); 9: return host; 10: } 11: } 12:  1: public class ServiceHostFactory : System.ServiceModel.Activation.ServiceHostFactory 2: { 3: 4: protected override System.ServiceModel.ServiceHost CreateServiceHost(Type serviceType, Uri[] baseAddresses) 5: { 6: var host = base.CreateServiceHost(serviceType, baseAddresses); 7: host.Description.Behaviors.Add(ServiceConfig.ServiceMetadataBehavior); 8: ServiceConfig.Configure((ServiceDebugBehavior)host.Description.Behaviors[typeof(ServiceDebugBehavior)]); 9: return host; 10: } 11: } 12: As you can see, we are using the same configuration helper we used when self-hosting. Now, when you have a factory, the <system.serviceModel> section of the configuration can be removed, because the section will be ignored when the service has a custom factory. If you want to configure something else in the config-file, one could configure in some other section.   Configuring the client Microsoft has helpfully created a ChannelFactory class in order to create a proxy client. When using this approach, you don't have generate those awfull proxy classes for the client. If you share the contracts with the server in it's own assembly like in the layer diagram under, you can share the same piece of code. The contracts in WCF are the interface to the service and if any, the datacontracts (custom types) the service depends on. Using the ChannelFactory with our configuration helper-class is very simple: 1: var identity = EndpointIdentity.CreateDnsIdentity("localhost"); 2: var endpointAddress = new EndpointAddress(endPoint, identity); 3: var factory = new ChannelFactory<IMyService>(DeployServiceConfig.DefaultBinding, endpointAddress); 4: using (var myService = new factory.CreateChannel()) 5: { 6: myService.Hello(); 7: } 8: factory.Close();   Happy configuration!

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  • Java Applet Tower Defence Game needs tweeking

    - by Ephiras
    Hello :) i have made a tower defence Game for my computer science class as one of my major projects, but have encountered some rather fatal roadblocks. here they are creating a menu screen (class Menu) that can set the total number of enimies, the max number of towers, starting money and the map. i tried creating a constructor in my Main class that sets all the values to whatever the Menu class passes in. I want the Menu screen to close after a difficulty has been selected and the main class to begin. Another problem i would really like some help with is instead of having to write entire arrays i would like to create a small segment of code that runs through an entire picture and sets up an array based on that pixels color.this way i can have multiple levels just dragged into a level folder and have the program read through them. users can even create their own. so a 1 if its yellow, a two if blue and a 3 if purple, then everything else = 0; you can download all the classes and code uif you'd like here sorry about having to redirect you but i wasn't sure how to efficently add a code spoiler. help is greatly appreciated

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  • Information Driven Value Chains: Achieving Supply Chain Excellence in the 21st Century With Oracle -

    World-class supply chains can help companies achieve top line and bottom line results in today’s complex,global world.Tune into this conversation with Rick Jewell,SVP,Oracle Supply Chain Development,to hear about Oracle’s vision for world class SCM,and the latest and greatest on Oracle Supply Chain Management solutions.You will learn about Oracle’s complete,best-in-class,open and integrated solutions,which are helping companies drive profitability,achieve operational excellence,streamline innovation,and manage risk and compliance in today’s complex,global world.

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  • Model View Control Issue: Null Pointer Initialization Question [closed]

    - by David Dimalanta
    Good morning again. This is David. Please, I need an urgent help regarding control model view where I making a code that uniquely separating into groups: An Activity Java Class to Display the Interface A View and Function Java Class for Drawing Cards and Display it on the Activity Class The problem is that the result returns a Null Pointer Exception. I have initialize for the ID for Text View and Image View. Under this class "draw_deck.java". Please help me. Here's my code for draw_deck.java: package com.bodapps.inbetween.model; import android.content.Context; import android.view.View; import android.widget.ImageView; import android.widget.TextView; import com.bodapps.inbetween.R; public class draw_deck extends View { public TextView count_label; public ImageView draw_card; private int count; public draw_deck(Context context) { super(context); // TODO Auto-generated constructor stub //I have initialized two widgets for ID. I still don't get it why I got forced closed by Null Pointer Exception thing. draw_card = (ImageView) findViewById(R.id.IV_Draw_Card); count_label = (TextView) findViewById(R.id.Text_View_Count_Card); } public void draw(int s, int c, String strSuit, String strValue, Pile pile, Context context) { //super(context); //Just printing the card drawn from pile int suit, value = 1; draw_card = (ImageView) findViewById(R.id.IV_Draw_Card); count_label = (TextView) findViewById(R.id.Text_View_Count_Card); Card card; if(!pile.isEmpty()) //Setting it to IF statement displays the card one by one. { card = pile.drawFromPile(); //Need to check first if card is null. if (card != null) { //draws an extra if (card != null) { //Get suit of card to print out. suit = card.getSuit(); switch (suit) { case CardInfo.DIAMOND: strSuit = "DIAMOND"; s=0; break; case CardInfo.HEART: strSuit = "HEART"; s=1; break; case CardInfo.SPADE: strSuit = "SPADE"; s=2; break; case CardInfo.CLUB: strSuit = "CLUB"; s=3; break; } //Get value of card to print out. value = card.getValue(); switch (value) { case CardInfo.ACE: strValue = "ACE"; c=0; break; case CardInfo.TWO: c=1; break; case CardInfo.THREE: strValue = "THREE"; c=2; break; case CardInfo.FOUR: strValue = "FOUR"; c=3; break; case CardInfo.FIVE: strValue = "FIVE"; c=4; break; case CardInfo.SIX: strValue = "SIX"; c=4; break; case CardInfo.SEVEN: strValue = "SEVEN"; c=4; break; case CardInfo.EIGHT: strValue = "EIGHT"; c=4; break; case CardInfo.NINE: strValue = "NINE"; c=4; break; case CardInfo.TEN: strValue = "TEN"; c=4; break; case CardInfo.JACK: strValue = "JACK"; c=4; break; case CardInfo.QUEEN: strValue = "QUEEN"; c=4; break; case CardInfo.KING: strValue = "KING"; c=4; break; } } } }// //Below two lines of code, this is where issued the Null Pointer Exception. draw_card.setImageResource(deck[s][c]); count_label.setText(new StringBuilder(strValue).append(" of ").append(strSuit).append(String.valueOf(" " + count++)).toString()); } //Choice of Suits in a Deck public Integer[][] deck = { //Array Group 1 is [0][0] (No. of Cards: 4 - DIAMOND) { R.drawable.card_dummy_1, R.drawable.card_dummy_2, R.drawable.card_dummy_4, R.drawable.card_dummy_5, R.drawable.card_dummy_3 }, //Array Group 2 is [1][0] (No. of Cards: 4 - HEART) { R.drawable.card_dummy_1, R.drawable.card_dummy_2, R.drawable.card_dummy_4, R.drawable.card_dummy_5, R.drawable.card_dummy_3 }, //Array Group 3 is [2][0] (No. of Cards: 4 - SPADE) { R.drawable.card_dummy_1, R.drawable.card_dummy_2, R.drawable.card_dummy_4, R.drawable.card_dummy_5, R.drawable.card_dummy_3 }, //Array Group 4 is [3][0] (No. of Cards: 4 - CLUB) { R.drawable.card_dummy_1, R.drawable.card_dummy_2, R.drawable.card_dummy_4, R.drawable.card_dummy_5, R.drawable.card_dummy_3 }, }; } And this one of the activity class, Player_Mode_2.java: package com.bodapps.inbetween; import java.util.Random; import android.app.Activity; import android.app.Dialog; import android.content.Context; import android.os.Bundle; import android.view.View; import android.view.View.OnClickListener; import android.widget.Button; import android.widget.EditText; import android.widget.ImageView; import android.widget.TextView; import android.widget.Toast; import com.bodapps.inbetween.model.Card; import com.bodapps.inbetween.model.Pile; import com.bodapps.inbetween.model.draw_deck; /* * * Public class for Two-Player mode. * */ public class Player_Mode_2 extends Activity { //Image Views private ImageView draw_card; private ImageView player_1; private ImageView player_2; private ImageView icon; //Buttons private Button set_deck; //Edit Texts private EditText enter_no_of_decks; //text Views private TextView count_label; //Integer Data Types private int no_of_cards, count; private int card_multiplier; //Contexts final Context context = this; //Pile Model public Pile pile; //Card Model public Card card; //create View @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.play_2_player_mode); //-----[ Search for Views ]----- //Initialize for Image View draw_card = (ImageView) findViewById(R.id.IV_Draw_Card); player_1 = (ImageView) findViewById(R.id.IV_Player_1_Card); player_2 = (ImageView) findViewById(R.id.IV_Player_2_Card); //Initialize for Text view or Label count_label = (TextView) findViewById(R.id.Text_View_Count_Card); //-----[ Adding Values ]----- //Integer Values count = 0; no_of_cards = 0; //-----[ Adding Dialog ]----- //Initializing Dialog final Dialog deck_dialog = new Dialog(context); deck_dialog.setContentView(R.layout.dialog); deck_dialog.setTitle("Deck Dialog"); //-----[ Initializing Views for Dialog's Contents ]----- //Initialize for Edit Text enter_no_of_decks = (EditText) deck_dialog.findViewById(R.id.Edit_Text_Set_Number_of_Decks); //Initialize for Button set_deck = (Button) deck_dialog.findViewById(R.id.Button_Deck); //-----[ Setting onClickListener() ]----- //Set Event Listener for Image view draw_card.setOnClickListener(new Draw_Card_Model()); //Set Event Listener for Setting the Deck set_deck.setOnClickListener(new OnClickListener() { public void onClick(View v) { if(card_multiplier <= 8) { //Use "Integer.parseInt()" method to instantly convert from String to int value. card_multiplier = Integer.parseInt(enter_no_of_decks.getText().toString()); //Shuffling cards... pile = new Pile(card_multiplier); //Multiply no. of decks //Dismiss or close the dialog. deck_dialog.dismiss(); } else { Toast.makeText(getApplicationContext(), "Please choose a number from 1 to 8.", Toast.LENGTH_SHORT).show(); } } }); //Show dialog. deck_dialog.show(); } //Shuffling the Array public void Shuffle_Cards(Integer[][] Shuffle_Deck) { Random random = new Random(); for(int i = Shuffle_Deck[no_of_cards].length - 1; i >=0; i--) { int Index = random.nextInt(i + 1); //Simple Swapping Integer swap = Shuffle_Deck[card_multiplier-1][Index]; Shuffle_Deck[card_multiplier-1][Index] = Shuffle_Deck[card_multiplier-1][i]; Shuffle_Deck[card_multiplier-1][i] = swap; } } //Private Class for Random Card Draw private class Draw_Card_Model implements OnClickListener { public void onClick(View v) { //Just printing the card drawn from pile int suit = 0, value = 0; String strSuit = "", strValue = ""; draw_deck draw = new draw_deck(context); //This line is where issued the Null Pointer Exception. if (count == card_multiplier*52) { // A message shows up when all cards are draw out. Toast.makeText(getApplicationContext(), "All cards have been used up.", Toast.LENGTH_SHORT).show(); draw_card.setEnabled(false); } else { draw.draw(suit, value, strSuit, strValue, pile, context); count_label.setText(count); //This is where I got force closed error, although "int count" have initialized the number. This was supposed to accept in the setText() method. count++; } } } } Take note that the issues on Null Pointer Exception is the Image View and the Edit Text. I got to test it. Thanks. If you have any info about my question, let me know it frankly.

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  • Where should you put constants and why?

    - by Tim Meyer
    In our mostly large applications, we usually have a only few locations for constants: One class for GUI and internal contstants (Tab Page titles, Group Box titles, calculation factors, enumerations) One class for database tables and columns (this part is generated code) plus readable names for them (manually assigned) One class for application messages (logging, message boxes etc) The constants are usually separated into different structs in those classes. In our C++ applications, the constants are only defined in the .h file and the values are assigned in the .cpp file. One of the advantages is that all strings etc are in one central place and everybody knows where to find them when something must be changed. This is especially something project managers seem to like as people come and go and this way everybody can change such trivial things without having to dig into the application's structure. Also, you can easily change the title of similar Group Boxes / Tab Pages etc at once. Another aspect is that you can just print that class and give it to a non-programmer who can check if the captions are intuitive, and if messages to the user are too detailed or too confusing etc. However, I see certain disadvantages: Every single class is tightly coupled to the constants classes Adding/Removing/Renaming/Moving a constant requires recompilation of at least 90% of the application (Note: Changing the value doesn't, at least for C++). In one of our C++ projects with 1500 classes, this means around 7 minutes of compilation time (using precompiled headers; without them it's around 50 minutes) plus around 10 minutes of linking against certain static libraries. Building a speed optimized release through the Visual Studio Compiler takes up to 3 hours. I don't know if the huge amount of class relations is the source but it might as well be. You get driven into temporarily hard-coding strings straight into code because you want to test something very quickly and don't want to wait 15 minutes just for that test (and probably every subsequent one). Everybody knows what happens to the "I will fix that later"-thoughts. Reusing a class in another project isn't always that easy (mainly due to other tight couplings, but the constants handling doesn't make it easier.) Where would you store constants like that? Also what arguments would you bring in order to convince your project manager that there are better concepts which also comply with the advantages listed above? Feel free to give a C++-specific or independent answer. PS: I know this question is kind of subjective but I honestly don't know of any better place than this site for this kind of question. Update on this project I have news on the compile time thing: Following Caleb's and gbjbaanb's posts, I split my constants file into several other files when I had time. I also eventually split my project into several libraries which was now possible much easier. Compiling this in release mode showed that the auto-generated file which contains the database definitions (table, column names and more - more than 8000 symbols) and builds up certain hashes caused the huge compile times in release mode. Deactivating MSVC's optimizer for the library which contains the DB constants now allowed us to reduce the total compile time of your Project (several applications) in release mode from up to 8 hours to less than one hour! We have yet to find out why MSVC has such a hard time optimizing these files, but for now this change relieves a lot of pressure as we no longer have to rely on nightly builds only. That fact - and other benefits, such as less tight coupling, better reuseability etc - also showed that spending time splitting up the "constants" wasn't such a bad idea after all ;-)

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  • C++11 Tidbits: Decltype (Part 2, trailing return type)

    - by Paolo Carlini
    Following on from last tidbit showing how the decltype operator essentially queries the type of an expression, the second part of this overview discusses how decltype can be syntactically combined with auto (itself the subject of the March 2010 tidbit). This combination can be used to specify trailing return types, also known informally as "late specified return types". Leaving aside the technical jargon, a simple example from section 8.3.5 of the C++11 standard usefully introduces this month's topic. Let's consider a template function like: template <class T, class U> ??? foo(T t, U u) { return t + u; } The question is: what should replace the question marks? The problem is that we are dealing with a template, thus we don't know at the outset the types of T and U. Even if they were restricted to be arithmetic builtin types, non-trivial rules in C++ relate the type of the sum to the types of T and U. In the past - in the GNU C++ runtime library too - programmers used to address these situations by way of rather ugly tricks involving __typeof__ which now, with decltype, could be rewritten as: template <class T, class U> decltype((*(T*)0) + (*(U*)0)) foo(T t, U u) { return t + u; } Of course the latter is guaranteed to work only for builtin arithmetic types, eg, '0' must make sense. In short: it's a hack. On the other hand, in C++11 you can use auto: template <class T, class U> auto foo(T t, U u) -> decltype(t + u) { return t + u; } This is much better. It's generic and a construct fully supported by the language. Finally, let's see a real-life example directly taken from the C++11 runtime library as implemented in GCC: template<typename _IteratorL, typename _IteratorR> inline auto operator-(const reverse_iterator<_IteratorL>& __x, const reverse_iterator<_IteratorR>& __y) -> decltype(__y.base() - __x.base()) { return __y.base() - __x.base(); } By now it should appear be completely straightforward. The availability of trailing return types in C++11 allowed fixing a real bug in the C++98 implementation of this operator (and many similar ones). In GCC, C++98 mode, this operator is: template<typename _IteratorL, typename _IteratorR> inline typename reverse_iterator<_IteratorL>::difference_type operator-(const reverse_iterator<_IteratorL>& __x, const reverse_iterator<_IteratorR>& __y) { return __y.base() - __x.base(); } This was guaranteed to work well with heterogeneous reverse_iterator types only if difference_type was the same for both types.

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  • Should I use an interface when methods are only similar?

    - by Joshua Harris
    I was posed with the idea of creating an object that checks if a point will collide with a line: public class PointAndLineSegmentCollisionDetector { public void Collides(Point p, LineSegment s) { // ... } } This made me think that if I decided to create a Box object, then I would need a PointAndBoxCollisionDetector and a LineSegmentAndBoxCollisionDetector. I might even realize that I should have a BoxAndBoxCollisionDetector and a LineSegmentAndLineSegmentCollisionDetector. And, when I add new objects that can collide I would need to add even more of these. But, they all have a Collides method, so everything I learned about abstraction is telling me, "Make an interface." public interface CollisionDetector { public void Collides(Spatial s1, Spatial s2); } But now I have a function that only detects some abstract class or interface that is used by Point, LineSegment, Box, etc.. So if I did this then each implementation would have to to a type check to make sure that the types are the appropriate type because the collision algorithm is different for each different type match up. Another solution could be this: public class CollisionDetector { public void Collides(Point p, LineSegment s) { ... } public void Collides(LineSegment s, Box b) { ... } public void Collides(Point p, Box b) { ... } // ... } But, this could end up being a huge class that seems unwieldy, although it would have simplicity in that it is only a bunch of Collide methods. This is similar to C#'s Convert class. Which is nice because it is large, but it is simple to understand how it works. This seems to be the better solution, but I thought I should open it for discussion as a wiki to get other opinions.

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  • Refactoring and Open / Closed principle

    - by Giorgio
    I have recently being reading a web site about clean code development (I do not put a link here because it is not in English). One of the principles advertised by this site is the Open Closed Principle: each software component should be open for extension and closed for modification. E.g., when we have implemented and tested a class, we should only modify it to fix bugs or to add new functionality (e.g. new methods that do not influence the existing ones). The existing functionality and implementation should not be changed. I normally apply this principle by defining an interface I and a corresponding implementation class A. When class A has become stable (implemented and tested), I normally do not modify it too much (possibly, not at all), i.e. If new requirements arrive (e.g. performance, or a totally new implementation of the interface) that require big changes to the code, I write a new implementation B, and keep using A as long as B is not mature. When B is mature, all that is needed is to change how I is instantiated. If the new requirements suggest a change to the interface as well, I define a new interface I' and a new implementation A'. So I, A are frozen and remain the implementation for the production system as long as I' and A' are not stable enough to replace them. So, in view of these observation, I was a bit surprised that the web page then suggested the use of complex refactorings, "... because it is not possible to write code directly in its final form." Isn't there a contradiction / conflict between enforcing the Open / Closed Principle and suggesting the use of complex refactorings as a best practice? Or the idea here is that one can use complex refactorings during the development of a class A, but when that class has been tested successfully it should be frozen?

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  • Confusion about inheritance

    - by Samuel Adam
    I know I might get downvoted for this, but I'm really curious. I was taught that inheritance is a very powerful polymorphism tool, but I can't seem to use it well in real cases. So far, I can only use inheritance when the base class is an abstract class. Examples : If we're talking about Product and Inventory, I quickly assumed that a Product is an Inventory because a Product must be inventorized as well. But a problem occured when user wanted to sell their Inventory item. It just doesn't seem to be right to change an Inventory object to it's subtype (Product), it's almost like trying to convert a parent to it's child. Another case is Customer and Member. It is logical (at least for me) to think that a Member is a Customer with some more privileges. Same problem occurred when user wanted to upgrade an existing Customer to become a Member. A very trivial case is the Employee case. Where Manager, Clerk, etc can be derived from Employee. Still, the same upgrading issue. I tried to use composition instead for some cases, but I really wanted to know if I'm missing something for inheritance solution here. My composition solution for those cases : Create a reference of Inventory inside a Product. Here I'm making an assumption about that Product and Inventory is talking in a different context. While Product is in the context of sales (price, volume, discount, etc), Inventory is in the context of physical management (stock, movement, etc). Make a reference of Membership instead inside Customer class instead of previous inheritance solution. Therefor upgrading a Customer is only about instantiating the Customer's Membership property. This example is keep being taught in basic programming classes, but I think it's more proper to have those Manager, Clerk, etc derived from an abstract Role class and make it a property in Employee. I found it difficult to find an example of a concrete class deriving from another concrete class. Is there any inheritance solution in which I can solve those cases? Being new in this OOP thing, I really really need a guidance. Thanks!

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  • OData &ndash; The easiest service I can create

    - by Jon Dalberg
    I wanted to create an OData service with the least amount of code so I fired up Visual Studio and got cracking. I decided to serve up a list of naughty words and make them read-only. Create a new web project. I created an empty MVC 2 application but MVC is not required for OData. Add a new WCF Data Service to the project. I named mine NastyWords.svc since I’m serving up a list of nasty words. Add a class to expose via the service: NastyWord 1: [DataServiceKey("Word")] 2: public class NastyWord 3: { 4: public string Word { get; set; } 5: }   I need to be able to uniquely identify instances of NastyWords for the DataService so I used the DataServiceKey attribute with the “Word” property as the key. I could have added an “ID” property which would have uniquely identified them and would then not need the “DataServiceKey” attribute because the DataService would apply some reflection and heuristics to guess at which property would be the unique identifier. However, the words themselves are unique so adding an “ID” property would be redundantly repetitive. Then I created a data source to expose my NastyWord objects to the service. This is just a simple class with IQueryable<T> properties exposing the entities for my service: 1: public class NastyWordsDataSource 2: { 3: private static IList<NastyWord> words = new List<NastyWord> 4: { 5: new NastyWord{ Word="crap"}, 6: new NastyWord{ Word="darn"}, 7: new NastyWord{ Word="hell"}, 8: new NastyWord{ Word="shucks"} 9: }; 10:   11: public NastyWordsDataSource() 12: { 13: NastyWords = words.AsQueryable(); 14: } 15:   16: public IQueryable<NastyWord> NastyWords { get; private set; } 17: }   Now I can go to the NastyWords.svc class and tell it which data source to use and which entities to expose: 1: public class NastyWords : DataService<NastyWordsDataSource> 2: { 3: // This method is called only once to initialize service-wide policies. 4: public static void InitializeService(DataServiceConfiguration config) 5: { 6: config.SetEntitySetAccessRule("*", EntitySetRights.AllRead); 7: config.DataServiceBehavior.MaxProtocolVersion = DataServiceProtocolVersion.V2; 8: } 9: }   Compile and browse to my NastWords.svc and weep with joy Now I can query my service just like any other OData service. Next time, I’ll modify this service to allow updates to sent so I can build up my list of nasty words. Enjoy!

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  • Augmenting functionality of subclasses without code duplication in C++

    - by Rob W
    I have to add common functionality to some classes that share the same superclass, preferably without bloating the superclass. The simplified inheritance chain looks like this: Element -> HTMLElement -> HTMLAnchorElement Element -> SVGElement -> SVGAlement The default doSomething() method on Element is no-op by default, but there are some subclasses that need an actual implementation that requires some extra overridden methods and instance members. I cannot put a full implementation of doSomething() in Element because 1) it is only relevant for some of the subclasses, 2) its implementation has a performance impact and 3) it depends on a method that could be overridden by a class in the inheritance chain between the superclass and a subclass, e.g. SVGElement in my example. Especially because of the third point, I wanted to solve the problem using a template class, as follows (it is a kind of decorator for classes): struct Element { virtual void doSomething() {} }; // T should be an instance of Element template<class T> struct AugmentedElement : public T { // doSomething is expensive and uses T virtual void doSomething() override {} // Used by doSomething virtual bool shouldDoSomething() = 0; }; class SVGElement : public Element { /* ... */ }; class SVGAElement : public AugmentedElement<SVGElement> { // some non-trivial check bool shouldDoSomething() { /* ... */ return true; } }; // Similarly for HTMLAElement and others I looked around (in the existing (huge) codebase and on the internet), but didn't find any similar code snippets, let alone an evaluation of the effectiveness and pitfalls of this approach. Is my design the right way to go, or is there a better way to add common functionality to some subclasses of a given superclass?

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  • Confused about implementing Single Responsibility Principle

    - by HichemSeeSharp
    Please bear with me if the question looks not well structured. To put you in the context of my issue: I am building an application that invoices vehicles stay duration in a parking. In addition to the stay service there are some other services. Each service has its own calculation logic. Here is an illustration (please correct me if the design is wrong): public abstract class Service { public int Id { get; set; } public bool IsActivated { get; set; } public string Name { get; set } public decimal Price { get; set; } } public class VehicleService : Service { //MTM : many to many public virtual ICollection<MTMVehicleService> Vehicles { get; set; } } public class StayService : VehicleService { } public class Vehicle { public int Id { get; set; } public string ChassisNumber { get; set; } public DateTime? EntryDate { get; set; } public DateTime? DeliveryDate { get; set; } //... public virtual ICollection<MTMVehicleService> Services{ get; set; } } Now, I am focusing on the stay service as an example: I would like to know at invoicing time which class(es) would be responsible for generating the invoice item for the service and for each vehicle? This should calculate the duration cost knowing that the duration could be invoiced partially so the like is as follows: not yet invoiced stay days * stay price per day. At this moment I have InvoiceItemsGenerator do everything but I am aware that there is a better design.

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  • Fixed Sized Buffer or Variable Buffers with C# Sockets

    - by Keagan Ladds
    I am busy designing a TCP Server class in C# that has events and allows the user of the class to define packets that the server can send a receive by registering a class that is derived from my "GenericPacket" class. My TCPListener uses Async methods such as .BeginReceive(..); My issue is that because I am using the .BeginReceive(); I need to specify a buffer size when I call the function. This means I cant read the whole packet if one of my defined packets is too big. I have thought of creating a fixed sized Header that gets read using .BeginRead(); and the read the rest using Stream.Read(); but this will lead to the whole server having to wait for this operation to complete. I would like to know if anyone has come across this before and I would appreciate any suggestions.

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  • Group method parameter or individual parameter?

    - by Nassign
    I would like to ask on method parameters design consideration. I am usually deciding between using individual variables as parameters versus grouping them to a class or dictionary as one parameter. Is there such a rule when you should use individual parameter against using a class or a dictionary to group the parameter? Individual parameter - Straight forward, strongly typed Dictionary parameter - Very extensible, like HTTP request but cannot be strongly typed. Class parameter - Extensible by adding member to the class parameter, strongly typed. I am looking for a design reference on when to use which? Note: I am not sure if this question is valid in programmers but I definitely think it would be closed in stackoverflow, If it is still not valid, please point me to the proper page.

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  • Designing a plug-in system

    - by madflame991
    I'm working on a Java project and I would like to add a plug-in system. More precisely, I would like to let the user design his own module, pack it into a jar, leave it in a "plugins/" subfolder of my application and be done with it. I've managed to get a child classloader to instantiate objects of classes located in external jars, but now I'm facing a design dilemma: Say Joe makes a plug-in and he packs it in joeplugin.jar. I would really like Joe to have a class named "instantiation.Factory" and I would also like everyone to have this class with this exact location and name. (This factory class obviously implements a interface that I provide and through it I get what I want from the plug-in.) If Joe wouldn't be restricted in this way I would have to look into his entire jar for some class that implements my factory interface and I don't want to imagine how complicated things get. So my question is: should I enforce a strict naming convention for this single class? I have no idea how plug-in systems work.

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  • Spring + JSR 303 Validation group is ignored [closed]

    - by nsideras
    we have a simple bean with JSR annotations public class CustomerDTO { private static final long serialVersionUID = 1L; private Integer id; @NotEmpty(message = "{customer.firstname.empty}") private String firstName; @NotEmpty(message = "{customer.lastname.empty}") private String lastName; @NotEmpty(groups={PasswordChange.class}, message="{password.empty}") private String password; @NotEmpty(groups={PasswordChange.class}, message="{confirmation.password.empty}") private String password2; } and we have a Spring Controller @RequestMapping(value="/changePassword", method = RequestMethod.POST) public String changePassword(@Validated({ PasswordChange.class }) @ModelAttribute("customerdto") CustomerDTO customerDTO, BindingResult result, Locale locale) { logger.debug("Change Password was submitted with information: " + customerDTO.toString()); try { passwordStrengthPolicy.checkPasswordStrength(locale, customerDTO.getPassword()); if (result.hasErrors()) { return "changePassword"; } logger.debug("Calling customer service changePassword: " + customerDTO); customerOnlineNewService.changePassword(customerDTO); } catch (PasswordNotChangedException e) { logger.error("Could not change password PasswordNotChangedException: " + customerDTO.toString()); return "changePassword"; } catch (PasswordNotSecureException e) { return "changePassword"; } return createRedirectViewPath("changePassword"); } Our problem is that when changePassword is invoked the validator ignores the group(PasswordChange.class) and validates only firstName and lastName which are not in the group. Any idea? Thank you very much for your time.

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  • Web Services Example - Part 2: Programmatic

    - by Denis T
    In this edition of the ADF Mobile blog we'll tackle part 2 of our Web Service examples.  In this posting we'll take a look at using a SOAP Web Service but calling it programmatically in code and parsing the return into a bean. Getting the sample code: Just click here to download a zip of the entire project.  You can unzip it and load it into JDeveloper and deploy it either to iOS or Android.  Please follow the previous blog posts if you need help getting JDeveloper or ADF Mobile installed.  Note: This is a different workspace than WS-Part1 Defining our Web Service: Just like our first installment, we are using the same public weather forecast web service provided free by CDYNE Corporation.  Sometimes this service goes down so please ensure you know it's up before reporting this example isn't working. We're going to concentrate on the same two web service methods, GetCityForecastByZIP and GetWeatherInformation. Defing the Application: The application setup is identical to the Weather1 version.  There are some improvements to the data that is displayed as part of this example though.  Now we are able to show the associated image along with each forecast line when using the Forecast By Zip feature.  We've also added the temperature Hi/Low values into the UI. Summary of Fundamental Changes In This Application The most fundamental change is that we're binding the UI to the Bean Data Controls instead of directly to the Web Service Data Controls.  This gives us much more flexibility to control the shape of the data and allows us to do caching of the data outside of the Web Service.  This way if your application is, say offline, your bean could still populate with data from a local cache and still show you some UI as opposed to completely failing because you don't have any connectivity. In general we promote this type of programming technique with ADF Mobile to insulate your application from any issues with network connectivity. What's different with this example? We have setup the Web Service DC the same way but now we have managed beans to process the data.  The following classes define the "Model" of our application:  CityInformation-CityForecast-Forecast, WeatherInformation-WeatherDescription.  We use WeatherBean for UI interaction to the model layer.  If you look through this example, we don't really do that much with the java code except use it to grab the image URL from the weather description.  In a more realistic example, you might be using some JDBC classes to persist the data to a local database. To have a good architecture it is always good to keep your model and UI layers separate.  This gets muddied if you start to use bindings on a page invoked from Java code and this java code starts to become your "model" layer.  Since bindings are page specific, your model layer starts to become entwined with your UI.  Not good!  To help with this, we've added some utility functions that let you invoke DC methods without having a binding and thus execute methods from your "model" layer without requiring a binding in your page definition.  We do this with the invokeDataControlMethod of the AdfmfJavaUtilities class.  An example of this method call is available in line 95 of WeatherInformation.java and line 93 of CityInformation.Java. What's a GenericType? Because Web Service Data Controls (and also URL Data Controls AKA REST) use generic name/value pairs to define their structure and don't have strongly typed objects, these are actually stored internally as GenericType objects.  The GenericType class is simply a property map of name/value pairs that can be hierarchical.  There are methods like getAttribute where you supply the index of the attribute or it's string property name.  Why is this important to know?  Because invokeDataControlMethod returns GenericType objects and developers either need to parse these GenericType objects themselves or use one of our helper functions. GenericTypeBeanSerializationHelper This class does exactly what it's name implies.  It's a helper class for developers to aid in serialization of GenericTypes to/from java objects.  This is extremely handy if you have a large GenericType object with many attributes (or you're just lazy like me!) and you just want to parse it out into a real java object you can use more easily.  Here you would use the fromGenericType method.  This method takes the class of the Java object you wish to return and the GenericType as parameters.  The method then parses through each attribute in the GenericType and uses reflection to set that same attribute in the Java class.  Then the method returns that new object of the class you specified.  This is obviously very handy to avoid a lot of shuffling code between GenericType and your own Java classes.  The reverse method, toGenericType is also available when you want to go the other way.  In this case you supply the string that represents the package location in the DataControl definition (Example: "MyDC.myParams.MyCollection") and then pass in the Java object you have that holds the data and a GenericType is returned to you.  Again, it will use reflection to calculate the attributes that match between the java class and the GenericType and call the getters/setters on those. Issues and Possible Improvements: In the next installment we'll show you how to make your web service calls asynchronously so your UI will fill dynamically when the service call returns but in the meantime you show the data you have locally in your bean fed from some local cache.  This gives your users instant delivery of some data while you fetch other data in the background.

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  • Name user object and user table correctly

    - by Marc
    It's maybe simple but I think about this every time I build a new application. How do you name the class for the current user of the application and for the orm class of the user table? Usually I have something like CurrentUser: Logged-in user, stored in session, info for last activity etc User: ORM Class (C# EF CodeFirst, but it doesn't matter) And yes, they could have the same name in different namespaces, but I don't really like that.

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