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  • Questions about identifying the components in MVC

    - by luiscubal
    I'm currently developing an client-server application in node.js, Express, mustache and MySQL. However, I believe this question should be mostly language and framework agnostic. This is the first time I'm doing a real MVC application and I'm having trouble deciding exactly what means each component. (I've done web applications that could perhaps be called MVC before, but I wouldn't confidently refer to them as such) I have a server.js that ties the whole application together. It does initialization of all other components (including the database connection, and what I think are the "models" and the "views"), receiving HTTP requests and deciding which "views" to use. Does this mean that my server.js file is the controller? Or am I mixing code that doesn't belong there? What components should I break the server.js file into? Some examples of code that's in the server.js file: var connection = mysql.createConnection({ host : 'localhost', user : 'root', password : 'sqlrevenge', database : 'blog' }); //... app.get("/login", function (req, res) { //Function handles a GET request for login forms if (process.env.NODE_ENV == 'DEVELOPMENT') { mu.clearCache(); } session.session_from_request(connection, req, function (err, session) { if (err) { console.log('index.js session error', err); session = null; } login_view.html(res, user_model, post_model, session, mu); //I named my view functions "html" for the case I might want to add other output types (such as a JSON API), or should I opt for completely separate views then? }); }); I have another file that belongs named session.js. It receives a cookies object, reads the stored data to decide if it's a valid user session or not. It also includes a function named login that does change the value of cookies. First, I thought it would be part of the controller, since it kind of dealt with user input and supplied data to the models. Then, I thought that maybe it was a model since it dealt with the application data/database and the data it supplies is used by views. Now, I'm even wondering if it could be considered a View, since it outputs data (cookies are part of HTTP headers, which are output)

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  • May I remove ads from feed in my news reader app?

    - by Mahdi Ghiasi
    I'm creating a News Reader app for Tablets and PCs. My app is fetching data from news sources by RSS feed of websites (in the server-side). But some of these sites are showing some advertising banners at the end of each article. Should I remove those banners from the feed? Am I legally/ethically allowed to do this? And what about If I want to put some other ads in my application? (Right at the end of each article) I mean, If I want to have my own advertising service... Update: And what if I use feed for content titles and summaries, but use other thing, like Readability API to show full article, and then put my own ads below content? (Readability gets the HTML page, and gives you a clean page without any ads and such.)

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  • Copy-and-Pasted Test Code: How Bad is This?

    - by joshin4colours
    My current job is mostly writing GUI test code for various applications that we work on. However, I find that I tend to copy and paste a lot of code within tests. The reason for this is that the areas I'm testing tend to be similar enough to need repetition but not quite similar enough to encapsulate code into methods or objects. I find that when I try to use classes or methods more extensively, tests become more cumbersome to maintain and sometimes outright difficult to write in the first place. Instead, I usually copy a big chunk of test code from one section and paste it to another, and make any minor changes I need. I don't use more structured ways of coding, such as using more OO-principles or functions. Do other coders feel this way when writing test code? Obviously I want to follow DRY and YAGNI principles, but I find that test code (automated test code for GUI testing anyway) can make these principles tough to follow. Or do I just need more coding practice and a better overall system of doing things? EDIT: The tool I'm using is SilkTest, which is in a proprietary language called 4Test. As well, these tests are mostly for Windows desktop applications, but I also have tested web apps using this setup as well.

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  • KISS principle applied to programming language design?

    - by Giorgio
    KISS ("keep it simple stupid", see e.g. here) is an important principle in software development, even though it apparently originated in engineering. Citing from the wikipedia article: The principle is best exemplified by the story of Johnson handing a team of design engineers a handful of tools, with the challenge that the jet aircraft they were designing must be repairable by an average mechanic in the field under combat conditions with only these tools. Hence, the 'stupid' refers to the relationship between the way things break and the sophistication available to fix them. If I wanted to apply this to the field of software development I would replace "jet aircraft" with "piece of software", "average mechanic" with "average developer" and "under combat conditions" with "under the expected software development / maintenance conditions" (deadlines, time constraints, meetings / interruptions, available tools, and so on). So it is a commonly accepted idea that one should try to keep a piece of software simple stupid so that it easy to work on it later. But can the KISS principle be applied also to programming language design? Do you know of any programming languages that have been designed specifically with this principle in mind, i.e. to "allow an average programmer under average working conditions to write and maintain as much code as possible with the least cognitive effort"? If you cite any specific language it would be great if you could add a link to some document in which this intent is clearly expressed by the language designers. In any case, I would be interested to learn about the designers' (documented) intentions rather than your personal opinion about a particular programming language.

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  • How to keep background requests in sequence

    - by Jason Lewis
    I'm faced with implementing interfaces for some rather archaic systems, for handling online deposits to stored value accounts (think campus card accounts for students). Here's my dilemma: stage 1 of the process involves passing the user off to a thrid-party site for the credit card transaction, like old-school PayPal. Step two involves using a proprietary protocol for communicating with a legacy system for conducting the actual deposit. Step two requires that each transaction have a unique sequence number, and that the requests' seqnums are in order. Since we're logging each transaction in Postgres, my first thought was to take a number from a sequence in the DB, guaranteeing uniqueness. But since we're dealing with web requests that might come in near-simultaneously, and since latency with the return from the off-ste payment processor is beyond our control, there's always the chance for a race condition in the order of requests passed back to the proprietary system, and if the seqnums are out of order, the request fails silently (brilliant, right?). I thought about enqueuing the requests in Redis and using Resque workers to process them (single worker, single process, so they are processed in order), but we need to be able to give the user feedback as to whether the transaction was processed successfully, so this seems less feasible to me. I've tried to make this application handle concurrency well (as much as possible for a Ruby on Rails app), but now we're in a situation where we have to interact with a system that is designed to be single process, single threaded, and sequential. If it at least gave an "out of order" error, I could just increment (or take the next value off the sequence), but it's designed to fail silently in the event of ANY error. We are handling timeouts in a way that blocks on I/O, but since the application uses multiple workers (Unicorn), that's no guarantee. Any ideas/suggestions would be appreciated.

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  • How to get feedback on mobile application

    - by Jason Crosby
    I am relatively new to programming. I have been programming with Java and Android for about 2 years now and just recently released my first app to the Google Play app store. I have passed the word on to everyone I know and posted a few times on Facebook about it. But I am not really seeing anyone install them. I love to code I'm not looking to have the next big time app, but it would be nice to get some installs and feedback/ratings so I can get an idea of how well its doing and if there are any fixes or improvements I can make. I thought about doing an AdMob campaign a couple times here and there at about $10 to $20 per day. But I'm not sure if that will generate any kind of worthwhile feedback. What other things could I be doing in order to get some feedback on my application? Thanks in advance for your help and suggestions.

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  • Where to place the R code for R+Sweave+LaTeX workflow

    - by claytontstanley
    I spent the last week learning 3 new tools: R, Sweave, and LaTeX. One question that came to my mind though when working through my first project: Where do I place the majority of the R code? The tutorials that I read online placed the majority of the R code in the LaTeX .Rnw file. However, I find having a bunch of R calculations in the LaTeX file distracting. What I do find extremely helpful (of course) is to call out to R code in the LaTeX file and embed the result. So the workflow I've been using is to place 99% of my R code in my .R file. I run that file first, save a bunch of calculations as objects, and output the .Rout file once finished (to save the work). Then when running Sweave, I load up that .Rout file, so that I have the majority of my calculations already completed and in the Sweave R session. Then my LaTeX callouts to R are quite simple: Just give me the XTable stored in 'res.table', or give me the result of an already-computed calculation stored in the variable 'res'. So I push towards the minimal amount of R code in the LaTex file possible, to achieve the desired result (embedding stats results in the LaTeX writeup). Does anyone have any experience with this approach? I'm just worried I might run into trouble further down the line, when I start really trying to load up and leverage this workflow.

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  • Is It "Wrong"/Bad Design To Put A Thread/Background Worker In A Class?

    - by Jetti
    I have a class that will read from Excel (C# and .Net 4) and in that class I have a background worker that will load the data from Excel while the UI can remain responsive. My question is as follows: Is it bad design to have a background worker in a class? Should I create my class without it and use a background worker to operate on that class? I can't see any issues really of creating my class this way but then again I am a newbie so I figured I would make sure before I continue on. I hope that this question is relevant here as I don't think it should be on stackoverflow as my code works, this just a design issue.

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  • Best practice Java - String array constant and indexing it

    - by Pramod
    For string constants its usual to use a class with final String values. But whats the best practice for storing string array. I want to store different categories in a constant array and everytime a category has been selected, I want to know which category it belongs to and process based on that. Addition : To make it more clear, I have a categories A,B,C,D,E which is a constant array. Whenever a user clicks one of the items(button will have those texts) I should know which item was clicked and do processing on that. I can define an enum(say cat) and everytime do if clickedItem == cat.A .... else if clickedItem = cat.B .... else if .... or even register listeners for each item seperately. But I wanted to know the best practice for doing handling these kind of problems.

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  • How does PHP5 fare with the earlier versions of the language

    - by Pankaj Upadhyay
    Many times, I like to learn PHP for web development but been drawn back due to comments like the following :- (Comments are just for reference and does not invite Flame-war) "PHP is good but generates spaghetti code" "PHP is nice but Python is marriage material" "PHP lags stuff that you get in other languages like C# or JAVA" But for PHP5 i have seen some promising comments. So, What my question is how does PHP5 fare with the earlier versions of the language and is it good enough now to learn for web development. NOTE:- No comparison of PHP with other languages is sorted here. Please comment just on PHP and it's comparison with itself

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  • How does PHP5 fare with earlier versions of the language

    - by Pankaj Upadhyay
    I would like to learn PHP for web development but have been drawn back because of comments like the following*: PHP is good but generates spaghetti code PHP is nice but Python is marriage material PHP lacks stuff that you get in other languages like C# or Java But for PHP5 I have seen some promising comments. So, my question is: How does PHP5 fare with earlier versions of the language and is it good enough now to learn for web development. * Comments are just for reference not to incite a flame war. No comparison of PHP with other languages is asked for here. Please comment just on PHP5 and how it compares with earlier versions.

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  • Accessing and controlling to the modem by ethernet connection

    - by iwd35
    I have a PC and I connectted to my modem (via ethernet cable). I want to prepare interface (VS2010) and I want to connect it and do the following: Modem access the admin page (IP: 192.168.1.1 password: admin password: admin) Wireless band (2.4GHz or 5GHz) changing Network mode (N-only, B/G/N- Mixed) changing channel changing (channel 1, 2,3, etc.) The project will be a desktop application. I will use VB .NET; modem model:cisco linksys wag320. How I can do it?

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  • Getting paid through Ltd or Umbrella company?

    - by Guy
    I am working for a company as a web dev consultant at the moment, and they asked me whether I want to get payed through the Umbrella company or through my Ltd. Which is better for me and why? The @David Thornley made a good point in comments. Don't forget that we are talking about web developing here. I am not sure how is it in UK, but in the country I am from, you get taxed differently for the stuff you do.

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  • Opinion of OSCON?

    - by 16bytes
    This year I have the opportunity to travel to the conference of my choice and thus far have been looking at OSCON. For those who have attended, what is your opinion of the conference? Any tips/tricks? Any tips to effectively plan what to see/attend? Any suggestions for lesser known conferences? As a working programmer, my interest is pretty general; I want to learn more about up-and-coming tech that I may have a chance to use and/or use more effectively.

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  • What do you need to know to get a job as a web developer

    - by Alex Foster
    What do you need to know to at the very least get your foot in the door? We're assuming for someone who doesn't have a college degree (yet) but will eventually get one. My guess is html, css, javascript, and php, and photoshop and dreamweaver, and sql. And being familiar with using a web host to have sites live, like knowing how to use cpanel. It's probably a very inaccurate and narrow guess but that's what i think right now. I don't know exactly.

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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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  • What makes for the ideal project? [closed]

    - by Hans Westerbeek
    I try to be careful when accepting assignments, to avoid mutual disappointment. So, I started to come up with a list of things that I consider ingredients for The Ideal Project: (in no particular order) What did I miss? What did I get wrong? Team size < 6 persons to avoid having too many meetings Team members must be dedicated to the project Gut-feeling-estimate (made by developers) of running period does not exceed 4 months. Projects longer than that tend to become open-ended, and are therefore not projects. Has a Product Owner who has mandate and is well-respected at their own company and who has a real interest in the long-term success of the project. Has no technical involvement from people that are not on the team. (yes that's you, Mr Architect That Doesn't Code) All the usual about quiet working conditions Exciting subject matter. Content management is just not as cool as controlling robots :)

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  • Web application deployment and Dependencies

    - by Reith
    I have a free software web application that using other free software scripts for appearance. I have trouble to decide whether should I copy source code of used scripts to my project main repository or list them as dependencies and ask user to install them himself? Since some of scripts solving browser compatibilities issues and I'm not a good web designer (i hate to check my web site on IE to see compatibility) using the newest version of scripts is preferable and second solution works here. But it has problem with scripts aren't backward-compatible with versions I've used them for development. Maybe another method is well-known for this issues that I don't know them.

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  • What are the basic skills a beginner JavaScript programmer should have?

    - by Sanford
    In NYC, we are working on creating a collaborative community programming environment and trying to segment out software engineers into differing buckets. At present, we are trying to define: Beginners Intermediates Advanced Experts (and/or Masters) Similar to an apprenticeship, you would need to demonstrate specific skills to achieve different levels. Right now, we have identified beginner programming skills as: Object - method, attributes, inheritance Variable - math, string, array, boolean - all are objects Basic arithmetic functions - precedence of functions String manipulation Looping - flow control Conditionals - boolean algebra This is a first attempt, and it is a challenge since we know the natural tension between programming and software engineering. How would you create such a skills-based ranking for JavaScript in this manner? For example, what would be the beginner JavaScript skills that you would need to have to advance to the intermediate training? And so on.

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  • what should a developer know/address to build commercial Android Apps ?

    - by giulio
    Android and mobile development is an exciting area of development. As it is a new discipline, what would be expected of an android developer to build commercially robust applications in terms of skills ? The problem that I and, i think, many other "noobs" into the technology would like to know are the areas of technical skills and the progression to the required advanced topics that goes beyond the the very basics provided by Google. There is a lot of information that's quite useful but its not organised into categories of discipline nor order.

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  • How useful are Lisp macros?

    - by compman
    Common Lisp allows you to write macros that do whatever source transformation you want. Scheme gives you a hygienic pattern-matching system that lets you perform transformations as well. How useful are macros in practice? Paul Graham said in Beating the Averages that: The source code of the Viaweb editor was probably about 20-25% macros. What sorts of things do people actually end up doing with macros?

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  • Check parameters annotated with @Nonnull for null?

    - by David Harkness
    We've begun using FindBugs with and annotating our parameters with @Nonnull appropriately, and it works great to point out bugs early in the cycle. So far we have continued checking these arguments for null using Guava's checkNotNull, but I would prefer to check for null only at the edges--places where the value can come in without having been checked for null, e.g., a SOAP request. // service layer accessible from outside public Person createPerson(@CheckForNull String name) { return new Person(Preconditions.checkNotNull(name)); } ... // internal constructor accessed only by the service layer public Person(@Nonnull String name) { this.name = Preconditions.checkNotNull(name); // remove this check? } I understand that @Nonnull does not block null values itself. However, given that FindBugs will point out anywhere a value is transferred from an unmarked field to one marked @Nonnull, can't we depend on it to catch these cases (which it does) without having to check these values for null everywhere they get passed around in the system? Am I naive to want to trust the tool and avoid these verbose checks? Bottom line: While it seems safe to remove the second null check below, is it bad practice? This question is perhaps too similar to Should one check for null if he does not expect null, but I'm asking specifically in relation to the @Nonnull annotation.

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  • Algorithm to infer tag hierarchy

    - by Tom
    I'm looking for an algorithm to infer a hierarchy from a set of tagged items. E.g. if the following items have the tags: 1 a 2 a,b 3 a,c 4 a,c,e 5 a,b 6 a,c 7 d 8 d,f Then I can construct an undirected graph (or graphs) by tallying the node weights and edge weights: node weights edge weights a 6 a-b 2 b 2 a-c 3 c 3 c-e 1 d 2 a-e 1 <-- this edge is parallel to a-c and c-e and not wanted e 1 d-f 1 f 1 The first problem is how to drop any redundant edges to get to the simplified graph? Note that it's only appropriate to remove that redundant a-e edge in this case because something is tagged as a-c-e, if that wasn't the case and the tag was a-e, that edge would have to remain. I suspect that means the removal of edges can only happen during the construction of the graph, not after everything has been tallied up. What I'd then like to do is identify the direction of the edges to create a directed graph (or graphs) and pick out root nodes to hopefully create a tree (or trees): trees a d // \\ | b c f \ e It seems like it could be a string algorithm - longest common subsequences/prefixes - or a tree/graph algorithm, but I am a little stuck since I don't know the correct terminology to search for it.

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  • Push-Based Events in a Services Oriented Architecture

    - by Colin Morelli
    I have come to a point, in building a services oriented architecture (on top of Thrift), that I need to expose events and allow listeners. My initial thought was, "create an EventService" to handle publishing and subscribing to events. That EventService can use whatever implementation it desires to actually distribute the events. My client automatically round-robins service requests to available service hosts which are determined using Zookeeper-based service discovery. So, I'd probably use JMS inside of EventService mainly for the purpose of persisting messages (in the event that a service host for EventService goes down before it can distribute the message to all of the available listeners). When I started considering this, I began looking into the differences between Queues and Topics. Topics unfortunately won't work for me, because (at least for now), all listeners must receive the message (even if they were down at the time the event was pushed, or hadn't made a subscription yet because they haven't completed startup (during deployment, for example) - messages should be queued until the service is available). However, I don't want EventService to be responsible for handling all of the events. I don't think it should have the code to react to events inside of it. Each of the services should do what it needs with a given event. This would indicate that each service would need a JMS connection, which questions the value of having EventService at all (as the services could individually publish and subscribe to JMS directly). However, it also couples all of the services to JMS (when I'd rather that there be a single service that's responsible for determining how to distribute events). What I had thought was to publish an event to EventService, which pulls a configuration of listeners from some configuration source (database, flat file, irrelevant for now). It replicates the message and pushes each one back into a queue with information specific to that listener (so, if there are 3 listeners, 1 event would become 3 events in JMS). Then, another thread in EventService (which is replicated, running on multiple hots) would be pulling from the queue, attempting to make the service call to the "listener", and returning the message to the queue (if the service is down), or discarding the message (if the listener completed successfully). tl;dr If I have an EventService that is responsible for receiving events and delegating service calls to "event listeners," (which are really just endpoints on other services), how should it know how to craft the service call? Should I create a generic "Event" object that is shared among all services? Then, the EventService can just construct this object and pass it to the service call. Or is there a better answer to this problem entirely?

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  • Is it a waste of time to free resources before I exit a process?

    - by Martin
    Let's consider a fictional program that builds a linked list in the heap, and at the end of the program there is a loop that frees all the nodes, and then exits. For this case let's say the linked list is just 500K of memory, and no special space managing is required. Is that a wast of time, because the OS will do that anyway? Will there be a different behavior later? Is that different according to the OS version? I'm mainly interested in UNIX based systems, but any information will be appreciated. I had today my first lesson in OS course and I'm wondering about that now.

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