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  • Factory Method Implementation

    - by cedar715
    I was going through the 'Factory method' pages in SO and had come across this link. And this comment. The example looked as a variant and thought to implement in its original way: to defer instantiation to subclasses... Here is my attempt. Does the following code implements the Factory pattern of the example specified in the link? Please validate and suggest if this has to undergo any re-factoring. public class ScheduleTypeFactoryImpl implements ScheduleTypeFactory { @Override public IScheduleItem createLinearScheduleItem() { return new LinearScheduleItem(); } @Override public IScheduleItem createVODScheduleItem() { return new VODScheduleItem(); } } public class UseScheduleTypeFactory { public enum ScheduleTypeEnum { CableOnDemandScheduleTypeID, BroadbandScheduleTypeID, LinearCableScheduleTypeID, MobileLinearScheduleTypeID } public static IScheduleItem getScheduleItem(ScheduleTypeEnum scheduleType) { IScheduleItem scheduleItem = null; ScheduleTypeFactory scheduleTypeFactory = new ScheduleTypeFactoryImpl(); switch (scheduleType) { case CableOnDemandScheduleTypeID: scheduleItem = scheduleTypeFactory.createVODScheduleItem(); break; case BroadbandScheduleTypeID: scheduleItem = scheduleTypeFactory.createVODScheduleItem(); break; case LinearCableScheduleTypeID: scheduleItem = scheduleTypeFactory.createLinearScheduleItem(); break; case MobileLinearScheduleTypeID: scheduleItem = scheduleTypeFactory.createLinearScheduleItem(); break; default: break; } return scheduleItem; } }

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  • Can per-user randomized salts be replaced with iterative hashing?

    - by Chas Emerick
    In the process of building what I'd like to hope is a properly-architected authentication mechanism, I've come across a lot of materials that specify that: user passwords must be salted the salt used should be sufficiently random and generated per-user ...therefore, the salt must be stored with the user record in order to support verification of the user password I wholeheartedly agree with the first and second points, but it seems like there's an easy workaround for the latter. Instead of doing the equivalent of (pseudocode here): salt = random(); hashedPassword = hash(salt . password); storeUserRecord(username, hashedPassword, salt); Why not use the hash of the username as the salt? This yields a domain of salts that is well-distributed, (roughly) random, and each individual salt is as complex as your salt function provides for. Even better, you don't have to store the salt in the database -- just regenerate it at authentication-time. More pseudocode: salt = hash(username); hashedPassword = hash(salt . password); storeUserRecord(username, hashedPassword); (Of course, hash in the examples above should be something reasonable, like SHA-512, or some other strong hash.) This seems reasonable to me given what (little) I know of crypto, but the fact that it's a simplification over widely-recommended practice makes me wonder whether there's some obvious reason I've gone astray that I'm not aware of.

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  • Throwing exception vs returning null value with switch statement

    - by Greg
    So I have function that formats a date to coerce to given enum DateType{CURRENT, START, END} what would be the best way to handling return value with cases that use switch statement public static String format(Date date, DateType datetype) { ..validation checks switch(datetype){ case CURRENT:{ return getFormattedDate(date, "yyyy-MM-dd hh:mm:ss"); } ... default:throw new ("Something strange happend"); } } OR throw excpetion at the end public static String format(Date date, DateType datetype) { ..validation checks switch(datetype){ case CURRENT:{ return getFormattedDate(date, "yyyy-MM-dd hh:mm:ss"); } ... } //It will never reach here, just to make compiler happy throw new IllegalArgumentException("Something strange happend"); } OR return null public static String format(Date date, DateType datetype) { ..validation checks switch(datetype){ case CURRENT:{ return getFormattedDate(date, "yyyy-MM-dd hh:mm:ss"); } ... } return null; } What would be the best practice here ? Also all the enum values will be handled in the case statement

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  • How convince other developers not to ignore Exceptions?

    - by Mnementh
    Recently I encountered a bug in an application I took over from another developer. I debugged for the reason and over an hour later I realized, that the problem wasn't the code producing the exception, but some code executed before this returning wrong data. If I dived into this, I encountered the following: try { ... } catch (XYException e){} If the Exception would have been propagated (a change I did), I would have found the reason for the bugs in a few minutes, as the stacktrace had pointed me to the problem. So how can I convince other developers to never catch and ignore exceptions in this way?

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  • Best practice for DAO pattern ?

    - by Tony
    I've seen a lot of codes use a service-dao pattern , I don't know the origin of this pattern . It force the front layer call service , then delegates some of the service task to dao. I want to ask : Does DAO layer do purely data access related task ? What about exception encapsulation ? Is there other pattern can be used to replace this ?

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  • Design pattern question: encapsulation or inheritance

    - by Matt
    Hey all, I have a question I have been toiling over for quite a while. I am building a templating engine with two main classes Template.php and Tag.php, with a bunch of extension classes like Img.php and String.php. The program works like this: A Template object creates a Tag objects. Each tag object determines which extension class (img, string, etc.) to implement. The point of the Tag class is to provide helper functions for each extension class such as wrap('div'), addClass('slideshow'), etc. Each Img or String class is used to render code specific to what is required, so $Img->render() would give something like <img src='blah.jpg' /> My Question is: Should I encapsulate all extension functionality within the Tag object like so: Tag.php function __construct($namespace, $args) { // Sort out namespace to determine which extension to call $this->extension = new $namespace($this); // Pass in Tag object so it can be used within extension return $this; // Tag object } function render() { return $this->extension->render(); } Img.php function __construct(Tag $T) { $args = $T->getArgs(); $T->addClass('img'); } function render() { return '<img src="blah.jpg" />'; } Usage: $T = new Tag("img", array(...); $T->render(); .... or should I create more of an inheritance structure because "Img is a Tag" Tag.php public static create($namespace, $args) { // Sort out namespace to determine which extension to call return new $namespace($args); } Img.php class Img extends Tag { function __construct($args) { // Determine namespace then call create tag $T = parent::__construct($namespace, $args); } function render() { return '<img src="blah.jpg" />'; } } Usage: $Img = Tag::create('img', array(...)); $Img->render(); One thing I do need is a common interface for creating custom tags, ie I can instantiate Img(...) then instantiate String(...), I do need to instantiate each extension using Tag. I know this is somewhat vague of a question, I'm hoping some of you have dealt with this in the past and can foresee certain issues with choosing each design pattern. If you have any other suggestions I would love to hear them. Thanks! Matt Mueller

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  • Database Replication OOD Pattern

    - by MrOnigiri
    Greetings fellow overflowers, After reading on MSDN about correct strategies on how to perform database replication, and understanding their suggestion on Master-Subordinate Incremental Replication. It left me wondering, what OOD design pattern should I use on this... The main elements of this strategy are the Acquirer, the Manipulator and the Writer. The first fetches data from the database and passes on to the second which might perform simple transformations to the data, before handling it to the final element, the writer, that writes the desired data on the destination Database. I thought about using the Chain of Responsibility pattern, but the Acquirer, Manipulator and Writer don't share a common role among theme, so It makes no sense. Should these elements be written as separate classes, or methods inside my service? Of course I'll be creating a DB Helper class as well, but that doesn't constitutes a problem. Wondering what your opinions on this are! Thanks for your replies

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  • How to include associative table information and still retain strong typing

    - by mwright
    I am using LINQ to SQL to create strongly typed objects in my project. Let's say I have an object that is represented by a database table. This object has a "Current State" that is kept in an associative table. I would like to make a single db call where I pull back the two tables joined but am unsure how I should be populating that information into some sort of object to preserve strong typing within my model so that the view using the information can just consume the information from the objects. I looked into creating a view model for this but it doesn't seem to quite fit. Am I thinking about this in the wrong way? What information can I include to help clarify my problem? Other details that may or may not be important: It's an MVC project....

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  • How to create custom javadoc tags

    - by Carlucho
    How to create custom javadoc tags such as @pre / @post... I found some links that explain it but i haven had luck with them, i dont know if that am already tired but i can figure where to put it. these are some of the links http://www.developer.com/java/other/article.php/3085991/Javadoc-Programming.html http://java.sun.com/j2se/1.5.0/docs/tooldocs/windows/javadoc.html I'm sorry to ask to be spoon fed but am at the stage where i only see black dots on the screen :\ Thanks a bunch

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  • UML Class Relationships

    - by 01010011
    Hi, I would like to confirm whether I am on the right track when identifying common UML class relationships. For example, is the relationship between: 1 a stackoverflow member and his/her stackoverflow user account categorized as a composition relationship or an aggregation relationship? At first I thought it was an association because this member "has a" account. However on second thought, I am thinking its composition because each "part" (user account) belongs to only one whole (user) at a time, meaning for as long as I am logged into stackoverflow, I have to use this one and only account until I log off. If I log back onto stackoverflow with a different account then its composition again. Do you agree? 2 a database and a person's user account an aggregation relationship? I think so because 1 database (the whole) can store 0...* number of user accounts (the parts) but another database can store the same user accounts. Finally, can anyone recommend a website that specializes in designing code using UML? Thanks in advance

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  • Gmail-like labelling system

    - by Dimitris
    Hi I am looking into a number of ways to implement a labelling system similar to the one in Gmail. Basically I have a Resource at the lowest level and I would like to provide a number of organisational groupings for that resource in the form of labels. If anyone has implemented something like that I would like to hear your views. My idea is to have within the Resource instance a List<Label>. I need to have an efficient mechanism in order to do very fast searches based on the labels or based on the resources. Thanks Dimitris

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  • Legacy code - when to move on

    - by Mmarquee
    My team and support a large number of legacy applications all of which are currently functional but problematic to support and maintain. They all depend on code that the compiler manufacture has officially no support for. So the question is should we leave the code as is, and risk a new compiler breaking our code, or should we bite the bullet and update all the code?

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  • Controls added in the designer are null during Page_Load

    - by mwright
    All of the names below are generic and not the actual names used. I have a custom UserControl with a Panel that contains a a couple Labels, both .aspx controls. .aspx: <asp:Panel runat="server"> <asp:Label ID="label1" runat="server"> </asp:Label> </asp:Panel> <asp:Panel runat="server"> <asp:Label ID="label2" runat="server"> </asp:Label> </asp:Panel> Codebehind: private readonly Object object; protected void Page_Load(object sender, EventArgs e) { // These are the lines that are failing // label1 and label2 are null label1.Text = object.Value1; label2.Text = object.Value2; } public ObjectRow(Object objectToDisplay) { object = objectToDisplay; } On another page, in the code behind, I create a new instance of the custom user control. protected void Page_Load(object sender, EventArgs e) { CustomControl control = new CustomControl(object); } The user control takes the parameter and attempts to set the labels based off of the object passed in. The labels that it tries to assign the values to are however, null. Is this an ASP.net lifecycle issue that I'm not understanding? My understanding based on the Microsoft ASP.net lifecycle page was that page controls were available after the Page_Initialization. What is the proper way to do this? Is there a better way?

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  • What is the best software design to use in this scenario

    - by domdefelice
    I need to generate HTML snippets using jQuery. The creation of those snippets depends on some data. The data is stored server-side, in session (where PHP is used). At the moment I achieved this - retrieving the data from the server via AJAX in form of JSON - and building the snippets via specific javascript functions that read those data The problem is that the complexity of the data is getting bigger and hence the serialization into JSON is getting even more difficult since I can't do it automatically. I can't do it automatically because some information are sensible so I generate a "stripped" version to send to the client. I know it is difficult to understand without any code to read, but I am hoping this is a common scenario and would be glad for any tip, suggestion or even design-pattern you can give me. Should I store both a complete and a stripped data on the server and then use some library to automatically generate the JSON from the stripped data? But this also means I have to get the two data synchronized. Or maybe I could move the logic server-side, this way avoiding sending the data. But this means sending javascript code (since I rely on jQuery). Maybe not a good idea. Feel free to ask me more details if this is not clear. Thank you for any help

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  • Best style for Python programs: what do you suggest?

    - by Noctis Skytower
    A friend of mine wanted help learning to program, so he gave me all the programs that he wrote for his previous classes. The last program that he wrote was an encryption program, and after rewriting all his programs in Python, this is how his encryption program turned out (after adding my own requirements). #! /usr/bin/env python ################################################################################ """\ CLASS INFORMATION ----------------- Program Name: Program 11 Programmer: Stephen Chappell Instructor: Stephen Chappell for CS 999-0, Python Due Date: 17 May 2010 DOCUMENTATION ------------- This is a simple encryption program that can encode and decode messages.""" ################################################################################ import sys KEY_FILE = 'Key.txt' BACKUP = '''\ !"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNO\ PQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~ _@/6-UC'GzaV0%5Mo9g+yNh8b">Bi=<Lx [sQn#^R.D2Xc(\ Jm!4e${lAEWud&t7]H\`}pvPw)FY,Z~?qK|3SOfk*:1;jTrI''' ################################################################################ def main(): "Run the program: loads key, runs processing loop, and saves key." encode_map, decode_map = load_key(KEY_FILE) try: run_interface_loop(encode_map, decode_map) except SystemExit: pass save_key(KEY_FILE, encode_map) def run_interface_loop(encode_map, decode_map): "Shows the menu and runs the appropriate command." print('This program handles encryption via a customizable key.') while True: print('''\ MENU ==== (1) Encode (2) Decode (3) Custom (4) Finish''') switch = get_character('Select: ', tuple('1234')) FUNC[switch](encode_map, decode_map) def get_character(prompt, choices): "Gets a valid menu option and returns it." while True: sys.stdout.write(prompt) sys.stdout.flush() line = sys.stdin.readline()[:-1] if not line: sys.exit() if line in choices: return line print(repr(line), 'is not a valid choice.') ################################################################################ def load_key(filename): "Gets the key file data and returns encoding/decoding dictionaries." plain, cypher = open_file(filename) return dict(zip(plain, cypher)), dict(zip(cypher, plain)) def open_file(filename): "Load the keys and tries to create it when not available." while True: try: with open(filename) as file: plain, cypher = file.read().split('\n') return plain, cypher except: with open(filename, 'w') as file: file.write(BACKUP) def save_key(filename, encode_map): "Dumps the map into two buffers and saves them to the key file." plain = cypher = str() for p, c in encode_map.items(): plain += p cypher += c with open(filename, 'w') as file: file.write(plain + '\n' + cypher) ################################################################################ def encode(encode_map, decode_map): "Encodes message for the user." print('Enter your message to encode (EOF when finished).') message = get_message() for char in message: sys.stdout.write(encode_map[char] if char in encode_map else char) def decode(encode_map, decode_map): "Decodes message for the user." print('Enter your message to decode (EOF when finished).') message = get_message() for char in message: sys.stdout.write(decode_map[char] if char in decode_map else char) def custom(encode_map, decode_map): "Allows user to edit the encoding/decoding dictionaries." plain, cypher = get_new_mapping() for p, c in zip(plain, cypher): encode_map[p] = c decode_map[c] = p ################################################################################ def get_message(): "Gets and returns text entered by the user (until EOF)." buffer = [] while True: line = sys.stdin.readline() if line: buffer.append(line) else: return ''.join(buffer) def get_new_mapping(): "Prompts for strings to edit encoding/decoding maps." while True: plain = get_unique_chars('What do you want to encode from?') cypher = get_unique_chars('What do you want to encode to?') if len(plain) == len(cypher): return plain, cypher print('Both lines should have the same length.') def get_unique_chars(prompt): "Gets strings that only contain unique characters." print(prompt) while True: line = input() if len(line) == len(set(line)): return line print('There were duplicate characters: please try again.') ################################################################################ # This map is used for dispatching commands in the interface loop. FUNC = {'1': encode, '2': decode, '3': custom, '4': lambda a, b: sys.exit()} ################################################################################ if __name__ == '__main__': main() For all those Python programmers out there, your help is being requested. How should the formatting (not necessarily the coding by altered to fit Python's style guide? My friend does not need to be learning things that are not correct. If you have suggestions on the code, feel free to post them to this wiki as well.

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  • How to design this class hierarchy?

    - by devoured elysium
    I have defined an Event class: Event and all the following classes inherit from Event: AEvent BEvent CEvent DEvent Now, with the info I gather from all these Event classes, I will make a chart. With AEvent and BEvent, I will generate points for that chart, while with CEvent and DEvent I will paint certain regions of the chart. Now, how should I signal this in my class hierarchy? Should I make AEvent and BEvent inherit from PointEvent while CEvent and DEvent inherit from RegionEvent, being that both RegionEvent and PointEvent inherit from Event? Should I add a field with an Enum to Event with 2 values, Point and Region, and each of the child classes set their value to it? Should I use some kind of pattern here? Which one? Thanks.

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  • Managing string resources in a Java application - singleton?

    - by Joe Attardi
    I seek a solution to the age-old problem of managing string resources. My current implementation seems to work well, but it depends on using singletons, and I know how often singletons can be maligned. The resource manager class has a singleton instance that handles lookups in the ResourceBundle, and you use it like so: MessageResources mr = MessageResources.getMessageResources(); // returns singleton instance ... JLabel helloLabel = new JLabel(mr.getString("label.hello")); Is this an appropriate use of a singleton? Is there some better, more universally used approach that I'm not aware of? I understand that this is probably a bit subjective, but any feedback I can get would be appreciated. I'd rather find out early on that I'm doing it wrong than later on in the process. Thanks!

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  • What software design pattern is best for the following scenario (C#)

    - by askjdh
    I have a gps device that records data e.g. datetime, latitude, longitude I have an sdk that reads the data from the device. The way the data is read: A command packet (basically a combination of int values in a struct) is sent to the device. The device responds with the data in fixed size chunks e.g. 64bytes Depending on the command issued I will get back differect data structs e.g. sending command 1 to the device returns a struct like struct x { id int, name char[20] } command 2 returns a collection of the following structs (basically it boils down to an array of the structs - y[12]) struct y { date datetime, lat decimal, lon decimal } I would then want to convert the struct to a class and save the data to a database. What would be the best way to encapsulate the entire process, preferably using some established design pattern? Many thanks M

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  • Interface for classes that have nothing in common

    - by Tomek Tarczynski
    Lets say I want to make few classes to determine behaviour of agents. The good practice would be to make some common interface for them, such interface (simplified) could look like this: interface IModel { void UpdateBehaviour(); } All , or at least most, of such model would have some parameters, but parameters from one model might have nothing in common with parameters of other model. I would like to have some common way of loading parameters. Question What is the best way to do that? Is it maybe just adding method void LoadParameters(object parameters) to the IModel? Or creating empty interface IParameters and add method void LoadParameters(IParameters parameters)? That are two ideas I came up with, but I don't like either of them.

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  • Strategy for unsubscribing event handlers

    - by stiank81
    In my WPF application I have a View that is given a ViewModel, and when given this View it adds event handlers to the ViewModel's PropertyChanged event. When some action occur in the GUI I remove the View and add another View to the holding container - where this new one is bound to the same ViewModel. After this has happened the old View still keeps handling PropertyChanged events in the ViewModel. I'm assuming this happens because the View hasn't been collected by the Garbage Collector yet, and therefore is alive? Well - I need it to stop. My assumption is that I need to manually detach the event handler from the ViewModel? Is there a best-practice on how to handle this?

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  • Managing of shared resources between classes?

    - by Axarydax
    Imagine that I have a several Viewer component that are used for displaying text and they have few modes that user can switch (different font presets for viewing text/binary/hex). What would be the best approach for managing shared objects - for example fonts, find dialog, etc? I figured that static class with lazily initialized objects would be OK, but this might be the wrong idea. static class ViewerStatic { private static Font monospaceFont; public static Font MonospaceFont { get { if (monospaceFont == null) //TODO read font settings from configuration monospaceFont = new Font(FontFamily.GenericMonospace, 9, FontStyle.Bold); return monospaceFont; } } private static Font sansFont; public static Font SansFont { get { if (sansFont == null) //TODO read font settings from configuration sansFont = new Font(FontFamily.GenericSansSerif, 9, FontStyle.Bold); return sansFont; } } }

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