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  • How to generate a Program template by generating an abstract class

    - by Byron-Lim Timothy Steffan
    i have the following problem. The 1st step is to implement a program, which follows a specific protocol on startup. Therefore, functions as onInit, onConfigRequest, etc. will be necessary. (These are triggered e.g. by incoming message on a TCP Port) My goal is to generate a class for example abstract one, which has abstract functions as onInit(), etc. A programmer should just inherit from this base class and should merely override these abstract functions of the base class. The rest as of the protocol e.g. should be simply handled in the background (using the code of the base class) and should not need to appear in the programmers code. What is the correct design strategy for such tasks? and how do I deal with, that the static main method is not inheritable? What are the key-tags for this problem? (I have problem searching for a solution since I lack clear statements on this problem) Goal is to create some sort of library/class, which - included in ones code - results in executables following the protocol. EDIT (new explanation): Okay let me try to explain more detailled: In this case programs should be clients within a client server architecture. We have a client server connection via TCP/IP. Each program needs to follow a specific protocol upon program start: As soon as my program starts and gets connected to the server it will receive an Init Message (TcpClient), when this happens it should trigger the function onInit(). (Should this be implemented by an event system?) After onInit() a acknowledgement message should be sent to the server. Afterwards there are some other steps as e.g. a config message from the server which triggers an onConfig and so on. Let's concentrate on the onInit function. The idea is, that onInit (and onConfig and so on) should be the only functions the programmer should edit while the overall protocol messaging is hidden for him. Therefore, I thought using an abstract class with the abstract methods onInit(), onConfig() in it should be the right thing. The static Main class I would like to hide, since within it e.g. there will be some part which connects to the tcp port, which reacts on the Init Message and which will call the onInit function. 2 problems here: 1. the static main class cant be inherited, isn it? 2. I cannot call abstract functions from the main class in the abstract master class. Let me give an Pseudo-example for my ideas: public abstract class MasterClass { static void Main(string[] args){ 1. open TCP connection 2. waiting for Init Message from server 3. onInit(); 4. Send Acknowledgement, that Init Routine has ended successfully 5. waiting for Config message from server 6..... } public abstract void onInit(); public abstract void onConfig(); } I hope you get the idea now! The programmer should afterwards inherit from this masterclass and merely need to edit the functions onInit and so on. Is this way possible? How? What else do you recommend for solving this? EDIT: The strategy ideo provided below is a good one! Check out my comment on that.

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  • Java Polymorphism - Selecting correct method based on subtype

    - by Marty Pitt
    Hi Given the following Class and Service layer signatures: public class PersonActionRequest { PersonVO person // ... other fields } public class MyServiceLayerClass { public void requestAction(PersonActionRequest request) { PersonVO abstractPerson = request.getPerson(); // call appropriate executeAction method based on subclass of PersonVO } private void executeAction(PersonVO person) {} private void executeAction(EmployeeVO employee) {} private void executeAction(ManagerVO manager) {} private void executeAction(UnicornWranglerVO unicornWrangler) {} } As discussed here, java will select the best method based on type info at compile time. (Ie., it will always select executeAction(PersonVO person) ). What's the most appropriate way to select the correct method? The internet tells me that using instanceof gets me slapped. However, I don't see the appropraite way to select the method without explictly casting abstractPerson to one of the other concrete types. Thanks Marty

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  • What's the most unsound program you've had to maintain?

    - by Robert Rossney
    I periodically am called upon to do maintenance work on a system that was built by a real rocket surgeon. There's so much wrong with it that it's hard to know where to start. No, wait, I'll start at the beginning: in the early days of the project, the designer was told that the system would need to scale, and he'd read that a source of scalability problems was traffic between the application and database servers, so he made sure to minimize this traffic. How? By putting all of the application logic in SQL Server stored procedures. Seriously. The great bulk of the application functions by the HTML front end formulating XML messages. When the middle tier receives an XML message, it uses the document element's tag name as the name of the stored procedure it should call, and calls the SP, passing it the entire XML message as a parameter. It takes the XML message that the SP returns and returns it directly back to the front end. There is no other logic in the application tier. (There was some code in the middle tier to validate the incoming XML messages against a library of schemas. But I removed it, after ascertaining that 1) only a small handful of messages had corresponding schemas, 2) the messages didn't actually conform to these schemas, and 3) after validating the messages, if any errors were encountered, the method discarded them. "This fuse box is a real time-saver - it comes from the factory with pennies pre-installed!") I've seen software that does the wrong thing before. Lots of it. I've written quite a bit. But I've never seen anything like the steely-eyed determination to do the wrong thing, at every possible turn, that's embodied in the design and programming of this system. Well, at least he went with what he knew, right? Um. Apparently, what he knew was Access. And he didn't really understand Access. Or databases. Here's a common pattern in this code: SELECT @TestCodeID FROM TestCode WHERE TestCode = @TestCode SELECT @CountryID FROM Country WHERE CountryAbbr = @CountryAbbr SELECT Invoice.*, TestCode.*, Country.* FROM Invoice JOIN TestCode ON Invoice.TestCodeID = TestCode.ID JOIN Country ON Invoice.CountryID = Country.ID WHERE Invoice.TestCodeID = @TestCodeID AND Invoice.CountryID = @CountryID Okay, fine. You don't trust the query optimizer either. But how about this? (Originally, I was going to post this in What's the best comment in source code you have ever encountered? but I realized that there was so much more to write about than just this one comment, and things just got out of hand.) At the end of many of the utility stored procedures, you'll see code that looks like the following: -- Fix NULLs SET @TargetValue = ISNULL(@TargetValue, -9999) Yes, that code is doing exactly what you can't allow yourself to believe it's doing lest you be driven mad. If the variable contains a NULL, he's alerting the caller by changing its value to -9999. Here's how this number is commonly used: -- Get target value EXEC ap_GetTargetValue @Param1, @Param2, OUTPUT @TargetValue -- Check target value for NULL value IF @TargetValue = -9999 ... Really. For another dimension of this system, see the article on thedailywtf.com entitled I Think I'll Call Them "Transactions". I'm not making any of this up. I swear. I'm often reminded, when I work on this system, of Wolfgang Pauli's famous response to a student: "That isn't right. It isn't even wrong." This can't really be the very worst program ever. It's definitely the worst one I've worked

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  • Writing temporary data from R

    - by Shane
    I want to write some temporary data to disk in an R package, and I want to be sure that it can run on every OS without assuming the user has admin rights. Is there an existing R function that can provide a path to a temporary directory on all major OS's? Or a way to reference a user's home directory? Otherwise, I was thinking of trying this: Sys.getenv("temp") I presume that I can't expect people to have write access to their R locations, otherwise I could reference a path within the package directory: .find.package("package.name").

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  • Problem with writing a hexadecimal string

    - by quilby
    Here is my code /* gcc -c -Wall -g main.c gcc -g -lm -o main main.o */ #include <stdlib.h> #include <stdio.h> #include <string.h> void stringToHex(const char* string, char* hex) { int i = 0; for(i = 0; i < strlen(string)/2; i++) { printf("s%x", string[2*i]); //for debugging sprintf(&hex[i], "%x", string[2*i]); printf("h%x\n", hex[i]); //for debugging } } void writeHex(char* hex, int length, FILE* file, long position) { fseek(file, position, SEEK_SET); fwrite(hex, sizeof(char), length, file); } int main(int argc, char** argv) { FILE* pic = fopen("hi.bmp", "w+b"); const char* string = "f2"; char hex[strlen(string)/2]; stringToHex(string, hex); writeHex(hex, strlen(string)/2, pic, 0); fclose(pic); return 0; } I want it to save the hexadecimal number 0xf2 to a file (later I will have to write bigger/longer numbers though). The program prints out - s66h36 And when I use hexedit to view the file I see the number '36' in it. Why is my code not working? Thanks!

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  • Is there a recommended way to use the Observer pattern in MVP using GWT?

    - by Tomislav Nakic-Alfirevic
    I am thinking about implementing a user interface according to the MVP pattern using GWT, but have doubts about how to proceed. These are (some of) my goals: - the presenter knows nothing about the UI technology (i.e. uses nothing from com.google.*) - the view knows nothing about the model or the presenter - the model knows nothing of the view or the presenter (...obviously) I would place an interface between the view and the presenter and use the Observer pattern to decouple the two: the view generates events and the presenter gets notified. What confuses me is that java.util.Observer and java.util.Observable are not supported in GWT. This suggests that what I'm doing is not the recommended way to do it, as far as GWT is concerned, which leads me to my questions: what is the recommended way to implement MVP using GWT, specifically with the above goals in mind? How would you do it?

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  • How to avoid having very large objects with Domain Driven Design

    - by Pablojim
    We are following Domain Driven Design for the implementation of a large website. However by putting the behaviour on the domain objects we are ending up with some very large classes. For example on our WebsiteUser object, we have many many methods - e.g. dealing with passwords, order history, refunds, customer segmentation. All of these methods are directly related to the user. Many of these methods delegate internally to other child object but this still results in some very large classes. I'm keen to avoid exposing lots of child objects e.g. user.getOrderHistory().getLatestOrder(). What other strategies can be used to avoid this problems?

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  • Pattern for managing reference count and object life

    - by Gopalakrishnan Subramani
    We have a serial port which is connected to hundreds of physical devices on the same wire. We have protocols like Modbus and Hart to handle the request and response between the application and devices. The question is related to managing the reference count of the channel. When no device is using the channel, the channel should be closed. public class SerialPortChannel { int refCount = 0; public void AddReference() { refCount++; } public void ReleaseReference() { refCount--; if (refCount <= 0) this.ReleasePort(); //This close the serial port } } For each device connected, we create a object for the device like device = new Device(); device.Attach(channel); //this calls channel.AddReference() When the device disconnect, device.Detach(channel); //this calls channel.ReleaseReference() I am not convinced by the reference count model. Are there any better way to handle this problem in .NET World?

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  • Displaying an NSString on a Custom View

    - by ilovetacos
    I have an interface that has an NSTextField, NSButton, and an NSView. When I type something in the textfield and press the button, I want the text to be drawn in the NSView. So far I have everything connected and working, except for the view. How can I connect the text and the view so that every time I press the button, the text is drawn to the view?

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  • Flex 3 / Air: Writing blank new lines to files using FileStream

    - by Edward
    I want to write some text directly to a file using Flex 3 / Air. The text on the file (call it "Database.txt") must have the following format: Line1 Line2 Line3 var FS:FileStream = new FileStream(); var DatabaseFile:File = File.desktopDirectory.resolvePath("Database.txt"); FS.open(DatabaseFile, FileMode.WRITE); FS.writeUTFBytes("Line1" + "\n" + "Line2" + "\n" + "Line3"); FS.close(); But it writes the following text to the file: Line1 Line2 Line3. I'm pretty sure I'm making a very dummy error, but I cannot figure out what it is. Can anyone help me? Thank you for your time :)

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  • Using DTOs and BOs

    - by ryanzec
    One area of question for me about DTOs/BOs is about when to pass/return the DTOs and when to pass/return the BOs. My gut reaction tells me to always map NHibernate to the DTOs, not BOs, and always pass/return the DTOs. Then whenever I needed to perform business logic, I would convert my DTO into a BO. The way I would do this is that my BO would have a have a constructor that takes a parameter that is the type of my interface (that defines the required fields/properties) that both my DTO and BO implement as the only argument. Then I would be able to create my BO by passing it the DTO in the constructor (since both with implement the same interface, they both with have the same properties) and then be able to perform my business logic with that BO. I would then also have a way to convert a BO to a DTO. However, I have also seen where people seem to only work with BOs and only work with DTOs in the background where to the user, it looks like there are no DTOs. What benefits/downfalls are there with this architecture vs always using BO's? Should I always being passing/returning either DTOs or BOs or mix and match (seems like mixing and matching could get confusing)?

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  • How build my own Application Setting

    - by adisembiring
    I want to build a ApplicationSetting for my application. The ApplicationSetting can be stored in a properties file or in a database table. The settings are stored in key-value pairs. E.g. ftp.host = blade ftp.username = dummy ftp.pass = pass content.row_pagination = 20 content.title = How to train your dragon. I have designed it as follows: Application settings reader: interface IApplicationSettingReader { read(); } DatabaseApplicationSettingReader { dao appSettingDao; AppSettings read() { List<AppSettingEntity> listEntity = appSettingsDao.findAll(); Map<String, String> map = new HaspMap<String, String>(); foreach (AppSettingEntity entity : listEntity) { map.put(entity.getConfigName(), entity.getConfigValue()); } return new AppSettings(map); } } DatabaseApplicationSettingReader { dao appSettingDao; AppSettings read() { //read from some properties file return new AppSettings(map); } } Application settings class: AppSettings { private static AppSettings instance; private Map map; Public AppSettings(Map map) { this.map = map; } public static AppSettings getInstance() { if (instance == null) { throw new RuntimeException("Object not configure yet"); } return instance; } public static configure(IApplicationSettingReader reader) { instance = reader.read(); } public String getFtpSetting(String param) { return map.get("ftp." + param); } public String getContentSetting(String param) { return map.get("content." + param); } } Test class: AppSettingsTest { IApplicationSettingReader reader; @Before public void setUp() throws Exception { reader = new DatabaseApplicationSettingReader(); } @Test public void getContentSetting_should_get_content_title() { AppSettings.configure(reader); Instance settings = AppSettings.getInstance(); String title = settings.getContentSetting("title"); assertNotNull(title); Sysout(title); } } My questions are: Can you give your opinion about my code, is there something wrong? I configure my application setting once, while the application start, I configure the application setting with appropriate reader (DbReader or PropertiesReader), I make it singleton. The problem is, when some user edit the database or file directly to database or file, I can't get the changed values. Now, I want to implement something like ApplicationSettingChangeListener. So if the data changes, I will refresh my application settings. Do you have any suggestions how this can be implemented?

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  • Design question what pattern to use

    - by rahul
    Problem Description: We have a requirement of storing the snapshot of an entity temporarily in the database untill a certain period of time untill all the processes to approve the data are completed. Once all approvals are completed the data shall be permanantly persisted into the actual table. Example: 1) Consider an entity called "User". One way to create the user is through the "Create Account Process". 2) The "Create Account Process" shall capture all the information of the User and store it in a temporary table in the database. 3) The data shall be used by the "Account Approval Process" to run its verification process. 4. After all the verification is completed successfully, the User data shall be persisted to the actual table. Question: Where to store the user data entered during "Create Account Process". Additionally, User data should be editable till the verification process is complete.

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  • xforms: how to prevent xxforms:default value from over-writing user input

    - by Purni
    I have a dropdown to display status, which can be Enabled(true) or Disabled(false). Here is my xml instance. <?xml version="1.0" encoding="UTF-8"?> <page> <file-name></file-name> <status></status> </page> By default, status should be true. So I have set it in binding as follows. <xforms:bind nodeset="./status" xxforms:default="true()" /> When user chooses Disabled in the dropdown, the status should get saved as false. Here is the xml that gets saved when I save the form. <page> <file-name>StatusDisabled.xml</file-name> <status>false</false> </page> When I open the form in edit mode, this is the xml I get in the XML inspector widget. <page> <file-name>StatusDisabled.xml</file-name> <status>true></status> </page> Status gets set to true because of xxforms:default, even though the xml is saved with a false value for status. How can I fix this? Here is the xhtml: <html xmlns="http://www.w3.org/1999/xhtml" xmlns:xforms="http://www.w3.org/2002/xforms" xmlns:xxforms="http://orbeon.org/oxf/xml/xforms"> <head> <title>XForms Default</title> <xforms:model> <xforms:instance id="instance"> <page> <name xmlns=""/> <status xmlns=""/> </page> </xforms:instance> <xforms:instance id="status-instance"> <items> <item label="Enabled" value="true" xmlns=""/> <item label="Disabled" value="false" xmlns=""/> </items> </xforms:instance> <xforms:bind nodeset="instance('instance')"> <xforms:bind nodeset="./status" xxforms:default="true()" /> </xforms:bind> </xforms:model> </head> <body> <p> <xforms:input ref="instance('instance')/name" incremental="true"> <xforms:label>Please enter your name:</xforms:label> </xforms:input> </p> <p> <xforms:select1 ref="instance('instance')/status" appearance="minimal" incremental="true"> <xforms:label>Please select status:</xforms:label> <xforms:itemset nodeset="instance('status-instance')/item"> <xforms:label ref="./@label"/> <xforms:value ref="./@value"/> </xforms:itemset> </xforms:select1> </p> </body> </html>

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  • What are good strategies for organizing single class per query service layer?

    - by KallDrexx
    Right now my Asp.net MVC application is structured as Controller - Services - Repositories. The services consist of aggregate root classes that contain methods. Each method is a specific operation that gets performed, such as retrieving a list of projects, adding a new project, or searching for a project etc. The problem with this is that my service classes are becoming really fat with a lot of methods. As of right now I am separating methods out into categories separated by #region tags, but this is quickly becoming out of control. I can definitely see it becoming hard to determine what functionality already exists and where modifications need to go. Since each method in the service classes are isolated and don't really interact with each other, they really could be more stand alone. After reading some articles, such as this, I am thinking of following the single query per class model, as it seems like a more organized solution. Instead of trying to figure out what class and method you need to call to perform an operation, you just have to figure out the class. My only reservation with the single query per class method is that I need some way to organize the 50+ classes I will end up with. Does anyone have any suggestions for strategies to best organize this type of pattern?

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  • Ruby: writing a network redirector

    - by Shyam
    Hi, I would like to research protocols such as HTTP. As I am learning Ruby, I would like to write a program that works as a "gateway". I would be connecting to it's port on for example 8080 and the program should forward my request to the real host and send back the answers. The idea of my design is something like this: class EchoProxy def run # run a listening socket on port 8080 myinfiniteloop end def myinfiniteloop # continually run this loop unless the app is terminated puts traffic end end Some pointers in the right direction would be great! Thank you for your comments, answers and feedback!

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  • Messaging pattern question

    - by Al Bundy
    Process A is calculating values for objects a1, a2, a3 etc. and is sending results to the middleware queue (RabbitMQ). Consumers read the queue and process these results further. Periodically process A has to send a snapshot of these values, so consumers could do some other calculations. Values for these objects might change independently. The queue might look like this a1, a1, a2, a1, a2, a2, a3... Consumers process each item in the queue. The snapshot has to contain all objects and consumers will process this message for all objects in one go. So the requirement is to have a queue like this: a1, a1, a3, a2, a2, [snapshot, a1, a2, a3], a3, a1 ... The problem is that these items are of different types: one type for objects like a1, a2 and other for a snapshot. This means that they should be processed in a diferent queues, but in that case there is a race condition: consumers might process objects before processing a snapshot. Is there any pattern to solve this (quite common) problem? We are using RabbitMQ for message queueing.

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  • When to release the model(representedObject) of the corresponding UIViewController.

    - by user313786
    Hi, In AppKit we have "representedObject" available through NSViewController, this representedObject is generally set to ModelController or the model which the NSViewController displays, this works great with bindings as you just set the new representedObject and model details are updated in the view, BUT in case of iPhone (UIKit, with NO Cocoa bindings available), there is no such representedObject in UIViewController so here are few things I am interested in knowing:- What is the best/recommended way of binding the model to the UIViewController?, preferably dont want to maintain lot of IBOutlets and calls setters to updated the changed model data for display in view. How/When should the related model of the UIViewController be released? When is the -[UIViewController dealloc] called, in the typical iPhone application. Am looking for architecting some classes so that the UIViewController coordinates between the view and the model, but at the same time, deallocs the model when ever not necessary. TIA.

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  • vs10 not deploying all required files - then not over-writing updated files

    - by justSteve
    I'm in the habit of deploying to alternating folders (/inetpub/wwwroot/mySite & /inetpub/wwwroot/mySite2) so if something unexpected happens with the deploy i can quickly swap back to a previous version just by changing the path in IIS So i was deploying an MVC2 webapp to a empty folder figuring that VS would send up all the files it needs. Not even close. Initially, it didn't even upload a couple required nHibernate.dlls. Later, after manually copying files referenced in the thrown exceptions, i just copied all the files from the previous compile and then re-published over the top expecting VS to over-write the changed files. Failed that too. No reports of errors by VS....just failed to over-write a number of pre-existing (but changed/updated) files. Hard to believe these kinds of errors (and lack of feedback that errors were encountered) in a state of the art tool like VS. Clearly, I'm doing something wrong. I'm using VisualSVN for source control and connect to my colocated server via a VPN-based mapped network drive (so I can use FileSystem to publish). (both of which can complicate file properties) VS08 had more choices for which files it would send up - i found i needed to use the 'All files in source' on an initial deployment, the 'Replace Matching'. If I choose 'delete all existing...' I'd be back to square 1 and have to deploy with the 'All files in source project folder'. But VS10 doesn't have the 'All files in source project folder. I ended up manually copying the files - which seems not right in the extreme. Are these known issues others have to deal with? What's best practice for deploying a web-app? thx

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  • Reducing the pain writing integration and system tests

    - by mdma
    I would like to make integration tests and system tests for my applications but producing good integration and system tests have often needed so much effort that I have not bothered. The few times I tried, I wrote custom, application-specific test harnesses, which felt like re-inventing the wheel each time. I wonder if this is the wrong approach. Is there a "standard" approach to integration and full system testing? EDIT: To clarify, it's automated tests, for desktop and web applications. Ideally a complete test suite that exercises the full functionality of the application.

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  • Designing a state machine in C++

    - by skyeagle
    I have a little problem that involves modelling a state machine. I have managed to do a little bit of knowledge engineering and 'reverse engineer' a set of primitive deterministic rules that determine state as well as state transitions. I would like to know what the best practises are regarding: How to rigorously test my states and state transitions to make sure that the system cannot end up in an undeetermined state. How to enforce state transition requirements (for example, it should be impossible to go directly from stateFoo to StateFooBar, i.e. to embue each state with 'knowlege' about the states it can transition to. Ideally, I would like to use clean, pattern based design, with templates wherever possible. I do need somewhere to start though and I would be grateful for any pointers (no pun intended), that are sent my way.

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  • ASP.NET MVC Paging for a search form

    - by James Alexander
    I've read several different posts on paging w/ in MVC but none describe a scenario where I have something like a search form and then want to display the results of the search criteria (with paging) beneath the form once the user clicks submit. My problem is that, the paging solution I'm using will create <a href="..."> links that will pass the desired page like so: http://mysite.com/search/2/ and while that's all fine and dandy, I don't have the results of the query being sent to the db in memory or anything so I need to query the DB again. If the results are handled by the POST controller action for /Search and the first page of the data is rendered as such, how do I get the same results (based on the form criteria specified by the user) when the user clicks to move to page 2? Some javascript voodoo? Leverage Session State? Make my GET controller action have the same variables expected by the search criteria (but optional), when the GET action is called, instantiate a FormCollection instance, populate it and pass it to the POST action method (there-by satisfying DRY)? Can someone point me in the right direction for this scenario or provide examples that have been implemented in the past? Thanks!

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  • Writing catch block with cleanup operations in Java ...

    - by kedarmhaswade
    I was not able to find any advise on catch blocks in Java that involve some cleanup operations which themselves could throw exceptions. The classic example is that of stream.close() which we usually call in the finally clause and if that throws an exception, we either ignore it by calling it in a try-catch block or declare it to be rethrown. But in general, how do I handle cases like: public void doIt() throws ApiException { //ApiException is my "higher level" exception try { doLower(); } catch(Exception le) { doCleanup(); //this throws exception too which I can't communicate to caller throw new ApiException(le); } } I could do: catch(Exception le) { try { doCleanup(); } catch(Exception e) { //ignore? //log? } throw new ApiException(le); //I must throw le } But that means I will have to do some log analysis to understand why cleanup failed. If I did: catch(Exception le) { try { doCleanup(); } catch(Exception e) { throw new ApiException(e); } It results in losing the le that got me here in the catch block in the fist place. What are some of the idioms people use here? Declare the lower level exceptions in throws clause? Ignore the exceptions during cleanup operation?

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