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• How do we keep dependent data structures up to date?

  - by Geo

  Suppose you have a parse tree, an abstract syntax tree, and a control flow graph, each one logically derived from the one before. In principle it is easy to construct each graph given the parse tree, but how can we manage the complexity of updating the graphs when the parse tree is modified? We know exactly how the tree has been modified, but how can the change be propagated to the other trees in a way that doesn't become difficult to manage? Naturally the dependent graph can be updated by simply reconstructing it from scratch every time the first graph changes, but then there would be no way of knowing the details of the changes in the dependent graph. I currently have four ways to attempt to solve this problem, but each one has difficulties. Nodes of the dependent tree each observe the relevant nodes of the original tree, updating themselves and the observer lists of original tree nodes as necessary. The conceptual complexity of this can become daunting. Each node of the original tree has a list of the dependent tree nodes that specifically depend upon it, and when the node changes it sets a flag on the dependent nodes to mark them as dirty, including the parents of the dependent nodes all the way down to the root. After each change we run an algorithm that is much like the algorithm for constructing the dependent graph from scratch, but it skips over any clean node and reconstructs each dirty node, keeping track of whether the reconstructed node is actually different from the dirty node. This can also get tricky. We can represent the logical connection between the original graph and the dependent graph as a data structure, like a list of constraints, perhaps designed using a declarative language. When the original graph changes we need only scan the list to discover which constraints are violated and how the dependent tree needs to change to correct the violation, all encoded as data. We can reconstruct the dependent graph from scratch as though there were no existing dependent graph, and then compare the existing graph and the new graph to discover how it has changed. I'm sure this is the easiest way because I know there are algorithms available for detecting differences, but they are all quite computationally expensive and in principle it seems unnecessary so I'm deliberately avoiding this option. What is the right way to deal with these sorts of problems? Surely there must be a design pattern that makes this whole thing almost easy. It would be nice to have a good solution for every problem of this general description. Does this class of problem have a name?

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• Current iOS version/device statistics?

  - by hotpaw2

  The answer to this SO question has become stale: iOS version/device statistics - where can i find? because time currency wasn't part of that question, and iOS version updates have been release since this question was asked. Is there a web site or other publicly available source which keeps a current or frequently updated list of the percentages of iOS devices and OS versions in use, perhaps by continual monitoring of app analytics or web site logs or other means? And what device or OS information are iOS app analytics currently allowed to report, if any? (...assuming an appropriate privacy policy and adhering to such, of course.)

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• Evaluating code for a graph [migrated]

  - by mazen.r.f

  This is relatively long code. Please take a look at this code if you are still willing to do so. I will appreciate your feedback. I have spent two days trying to come up with code to represent a graph, calculating the shortest path using Dijkstra's algorithm. But I am not able to get the right result, even though the code runs without errors. The result is not correct and I am always getting 0. I have three classes: Vertex, Edge, and Graph. The Vertex class represents the nodes in the graph and it has id and carried (which carry the weight of the links connected to it while using Dijkstra's algorithm) and a vector of the ids belong to other nodes the path will go through before arriving to the node itself. This vector is named previous_nodes. The Edge class represents the edges in the graph and has two vertices (one in each side) and a width (the distance between the two vertices). The Graph class represents the graph. It has two vectors, where one is the vertices included in this graph, and the other is the edges included in the graph. Inside the class Graph, there is a method named shortest() that takes the sources node id and the destination and calculates the shortest path using Dijkstra's algorithm. I think that it is the most important part of the code. My theory about the code is that I will create two vectors, one for the vertices in the graph named vertices, and another vector named ver_out (it will include the vertices out of calculation in the graph). I will also have two vectors of type Edge, where one is named edges (for all the edges in the graph), and the other is named track (to temporarily contain the edges linked to the temporary source node in every round). After the calculation of every round, the vector track will be cleared. In main(), I've created five vertices and 10 edges to simulate a graph. The result of the shortest path supposedly is 4, but I am always getting 0. That means I have something wrong in my code. If you are interesting in helping me find my mistake and making the code work, please take a look. The way shortest work is as follow: at the beginning, all the edges will be included in the vector edges. We select the edges related to the source and put them in the vector track, then we iterate through track and add the width of every edge to the vertex (node) related to it (not the source vertex). After that, we clear track and remove the source vertex from the vector vertices and select a new source. Then we start over again and select the edges related to the new source, put them in track, iterate over edges in track, adding the weights to the corresponding vertices, then remove this vertex from the vector vertices. Then clear track, and select a new source, and so on. #include<iostream> #include<vector> #include <stdlib.h> // for rand() using namespace std; class Vertex { private: unsigned int id; // the name of the vertex unsigned int carried; // the weight a vertex may carry when calculating shortest path vector<unsigned int> previous_nodes; public: unsigned int get_id(){return id;}; unsigned int get_carried(){return carried;}; void set_id(unsigned int value) {id = value;}; void set_carried(unsigned int value) {carried = value;}; void previous_nodes_update(unsigned int val){previous_nodes.push_back(val);}; void previous_nodes_erase(unsigned int val){previous_nodes.erase(previous_nodes.begin() + val);}; Vertex(unsigned int init_val = 0, unsigned int init_carried = 0) :id (init_val), carried(init_carried) // constructor { } ~Vertex() {}; // destructor }; class Edge { private: Vertex first_vertex; // a vertex on one side of the edge Vertex second_vertex; // a vertex on the other side of the edge unsigned int weight; // the value of the edge ( or its weight ) public: unsigned int get_weight() {return weight;}; void set_weight(unsigned int value) {weight = value;}; Vertex get_ver_1(){return first_vertex;}; Vertex get_ver_2(){return second_vertex;}; void set_first_vertex(Vertex v1) {first_vertex = v1;}; void set_second_vertex(Vertex v2) {second_vertex = v2;}; Edge(const Vertex& vertex_1 = 0, const Vertex& vertex_2 = 0, unsigned int init_weight = 0) : first_vertex(vertex_1), second_vertex(vertex_2), weight(init_weight) { } ~Edge() {} ; // destructor }; class Graph { private: std::vector<Vertex> vertices; std::vector<Edge> edges; public: Graph(vector<Vertex> ver_vector, vector<Edge> edg_vector) : vertices(ver_vector), edges(edg_vector) { } ~Graph() {}; vector<Vertex> get_vertices(){return vertices;}; vector<Edge> get_edges(){return edges;}; void set_vertices(vector<Vertex> vector_value) {vertices = vector_value;}; void set_edges(vector<Edge> vector_ed_value) {edges = vector_ed_value;}; unsigned int shortest(unsigned int src, unsigned int dis) { vector<Vertex> ver_out; vector<Edge> track; for(unsigned int i = 0; i < edges.size(); ++i) { if((edges[i].get_ver_1().get_id() == vertices[src].get_id()) || (edges[i].get_ver_2().get_id() == vertices[src].get_id())) { track.push_back (edges[i]); edges.erase(edges.begin()+i); } }; for(unsigned int i = 0; i < track.size(); ++i) { if(track[i].get_ver_1().get_id() != vertices[src].get_id()) { track[i].get_ver_1().set_carried((track[i].get_weight()) + track[i].get_ver_2().get_carried()); track[i].get_ver_1().previous_nodes_update(vertices[src].get_id()); } else { track[i].get_ver_2().set_carried((track[i].get_weight()) + track[i].get_ver_1().get_carried()); track[i].get_ver_2().previous_nodes_update(vertices[src].get_id()); } } for(unsigned int i = 0; i < vertices.size(); ++i) if(vertices[i].get_id() == src) vertices.erase(vertices.begin() + i); // removing the sources vertex from the vertices vector ver_out.push_back (vertices[src]); track.clear(); if(vertices[0].get_id() != dis) {src = vertices[0].get_id();} else {src = vertices[1].get_id();} for(unsigned int i = 0; i < vertices.size(); ++i) if((vertices[i].get_carried() < vertices[src].get_carried()) && (vertices[i].get_id() != dis)) src = vertices[i].get_id(); //while(!edges.empty()) for(unsigned int round = 0; round < vertices.size(); ++round) { for(unsigned int k = 0; k < edges.size(); ++k) { if((edges[k].get_ver_1().get_id() == vertices[src].get_id()) || (edges[k].get_ver_2().get_id() == vertices[src].get_id())) { track.push_back (edges[k]); edges.erase(edges.begin()+k); } }; for(unsigned int n = 0; n < track.size(); ++n) if((track[n].get_ver_1().get_id() != vertices[src].get_id()) && (track[n].get_ver_1().get_carried() > (track[n].get_ver_2().get_carried() + track[n].get_weight()))) { track[n].get_ver_1().set_carried((track[n].get_weight()) + track[n].get_ver_2().get_carried()); track[n].get_ver_1().previous_nodes_update(vertices[src].get_id()); } else if(track[n].get_ver_2().get_carried() > (track[n].get_ver_1().get_carried() + track[n].get_weight())) { track[n].get_ver_2().set_carried((track[n].get_weight()) + track[n].get_ver_1().get_carried()); track[n].get_ver_2().previous_nodes_update(vertices[src].get_id()); } for(unsigned int t = 0; t < vertices.size(); ++t) if(vertices[t].get_id() == src) vertices.erase(vertices.begin() + t); track.clear(); if(vertices[0].get_id() != dis) {src = vertices[0].get_id();} else {src = vertices[1].get_id();} for(unsigned int tt = 0; tt < edges.size(); ++tt) { if(vertices[tt].get_carried() < vertices[src].get_carried()) { src = vertices[tt].get_id(); } } } return vertices[dis].get_carried(); } }; int main() { cout<< "Hello, This is a graph"<< endl; vector<Vertex> vers(5); vers[0].set_id(0); vers[1].set_id(1); vers[2].set_id(2); vers[3].set_id(3); vers[4].set_id(4); vector<Edge> eds(10); eds[0].set_first_vertex(vers[0]); eds[0].set_second_vertex(vers[1]); eds[0].set_weight(5); eds[1].set_first_vertex(vers[0]); eds[1].set_second_vertex(vers[2]); eds[1].set_weight(9); eds[2].set_first_vertex(vers[0]); eds[2].set_second_vertex(vers[3]); eds[2].set_weight(4); eds[3].set_first_vertex(vers[0]); eds[3].set_second_vertex(vers[4]); eds[3].set_weight(6); eds[4].set_first_vertex(vers[1]); eds[4].set_second_vertex(vers[2]); eds[4].set_weight(2); eds[5].set_first_vertex(vers[1]); eds[5].set_second_vertex(vers[3]); eds[5].set_weight(5); eds[6].set_first_vertex(vers[1]); eds[6].set_second_vertex(vers[4]); eds[6].set_weight(7); eds[7].set_first_vertex(vers[2]); eds[7].set_second_vertex(vers[3]); eds[7].set_weight(1); eds[8].set_first_vertex(vers[2]); eds[8].set_second_vertex(vers[4]); eds[8].set_weight(8); eds[9].set_first_vertex(vers[3]); eds[9].set_second_vertex(vers[4]); eds[9].set_weight(3); unsigned int path; Graph graf(vers, eds); path = graf.shortest(2, 4); cout<< path << endl; return 0; }

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• Dealing with "I-am-cool-and-you-are-dumb" manager [closed]

  - by Software Guy

  I have been working with a software company for about 6 months now. I like the projects I work on there and I really like all the people there except for 1 guy. That guy is technically smart, and he is a co-founder of the company. He is an okay guy in person (the kind you wouldn't want to care about much) but things get tricky when he is your manager. In general I am all okay but there are times when I feel I am not being treated fairly: He doesn't give much thought to when he makes mistakes and when I do something similar, he is super critical. Recently he went as far as to say "I am not sure if I can trust you with this feature". The detais of this specific case are this: I was working on this feature, and I was already a couple of hours over my normal working hours, and then I decided to stop and continue tomorrow. We use git, and I like to commit changes locally and only push when I feel they are ready. This manager insists that I push all the changes to the central repo (in case my hard drive crashes). So I push the change, and the ticket is marked as "to be tested". Next day I come in, he sits next to me and starts complaining and says that I posted above. I really didn't know what to say, I tried to explain to him that the ticket is still being worked upon but he didn't seem to listen. He interrupts me in-between when I am coding, which I do not mind, but when I do that same, his face turns like this :| and reacts as if his work was super important and I am just wasting his time. He asks me to accumulate all questions, and then ask him altogether which is not always possible, as you need a clarification before you can continue on a feature implementation. And when I am coding, he talks on the phone with his customers next to me (when he can go to the meeting room with his laptop) and doesn't care. He made me switch to a whole new IDE (from Netbeans to a commercial IDE costing a lot of money) for a really tiny feature (which I later found out was in Netbeans as well!). I didn't make a big deal out of it as I am equally comfortable working with this new IDE, but I couldn't get the science behind his obsession. He said this feature makes sure that if any method is updated by a programmer, the IDE will turn the method name to red in places where it is used. I told him that I do not have a problem since I always search for method usage in the project and make sure its updated. IDEs even have refactoring features for exactly that, but... I recently implemented a feature for a project, and I was happy about it and considering him a senior, I asked him his comments about the implementation quality.. he thought long and hard, made a few funny faces, and when he couldn't find anything, he said "ummm, your program will crash if JS is disabled" - he was wrong, since I had made sure it would work fine with default values even if JS was disabled. I told him that and then he said "oh okay". BUT, the funny thing is, a few days back, he implemented something and I objected with "But that would not run if JS is disabled" and his response was "We don't have to care about people who disable JS" :-/ Once he asked me to investigate if there was a way to modify a CMS generated menu programmatically by extending the CMS, I did my research and told him that the only was is to inject a menu item using JavaScript / jQuery and his reaction was "ah that's ugly, and hacky, not acceptable" and two days later, I see that feature implemented in the same way as I had suggested. The point is, his reaction was not respectful at all, even if what I proposed was hacky, he should be respectful, that I know what's hacky and if I am suggesting something hacky, there must be a reason for it. There are plenty of other reasons / examples where I feel I am not being treated fairly. I want your advice as to what is it that I am doing wrong and how to deal with such a situation. The other guys in the team are actually very good people, and I do not want to leave the job either (although I could, if I want to). All I want is respect and equal treatment. I have thought about talking to this guy in a face to face meeting, but that worries me that his attitude might get worse and make things more difficult for me (since he doesn't seem to be the guy who thinks he can be wrong too). I am also considering talking to the other co-founder but I am not sure how he will take it (as both founders have been friends forever). Thanks for reading the long message, I really appreciate your help.

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• Trying to use OpenGL in Java on Netbeans but getting an error. Please help [migrated]

  - by Steven Rogers

  I am on a Mac running Netbeans 6.9. I downloaded and installed LWJGL using this tutorial down to the letter: http://lwjgl.org/wiki/index.php?title=Setting_Up_LWJGL_with_NetBeans I finished the installation and copied sample code to see if my system is working. I got a bug, and was not sure if it was because of faulty code or i was doing something wrong. So i shortened down the code to this little simple bit: package javaopengl; import org.lwjgl.Sys; import org.lwjgl.opengl.Display; //Testing public class Main { public static void main(String[] args) { boolean fullscreen = (args.length == 1 && args[0].equals("-fullscreen")); try { Display.create(); Display.destroy(); } catch (Exception e) { e.printStackTrace(System.err); } System.exit(0); } } But i still get the same error, this is the error that i get: run: Exception in thread "main" java.lang.NoClassDefFoundError: = Caused by: java.lang.ClassNotFoundException: = at java.net.URLClassLoader$1.run(URLClassLoader.java:202) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:190) at java.lang.ClassLoader.loadClass(ClassLoader.java:306) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301) at java.lang.ClassLoader.loadClass(ClassLoader.java:247) Java Result: 1 BUILD SUCCESSFUL (total time: 0 seconds) I am not sure what exactly is going on, Would you please tell me what is going on and how to fix it? It would be greatly appreciated, and thank you. Note: When i am looking at the text in the development environment, it does not show those red lines indicating there are any errors.

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• Do you use your personal laptop for work?

  - by davekaro

  We're trying to get our company to let us use our own personal laptop for client work. We've agreed that any code/data will be encrypted using something like TrueCrypt, in case the laptop is stolen or lost. However, the company is still skeptical and not sure they want to allow us to use our personal machines for development. They would rather buy us laptops... but we want to use MacBook Pros and they don't want to pay for them. Even if they did buy us laptops, we would stil have the issue of needing to encrypt the code/data in case of theft/loss. Do you use your own laptop for work? What are the arguments for/against this?

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• Concurrency with listeners and upload: is this solution sound?

  - by cbrulak

  I'm working on an Android app. We have listeners for position data and camera capture which is timed on a background thread (not a service). The timer thread dictates when the image is captured and also when the data is cached in a local sqlite db. So, my question is how to properly store the location data as it comes in based on the listeners and pull that data so that the database can be updated as the camera capture is executed. I can't put the location data into the database as it arrives because it is processed more frequently than the camera images and the camera images are what dominates the architecture at the moment. (Location data is supplement). However I need the location data to get a rough location of the where the image is captured. My first thought was to have singleton store the location data. And have a semaphore on the getInstance method so if the database update is happening (after an image is captured) we don't have an error. The location data can wait for the database update or it can be lost for that particular event it doesn't really matter. What are you thoughts? Am I on the right track? (And is this the right sub-site or would this be better on stackoverflow?)

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• Relationship between Repository and Unit of Work

  - by NullOrEmpty

  I am going to implement a repository, and I would like to use the UOW pattern since the consumer of the repository could do several operations, and I want to commit them at once. After read several articles about the matter, I still don't get how to relate this two elements, depending on the article it is being done in a way u other. Sometimes the UOW is something internal to the repository: public class Repository { UnitOfWork _uow; public Repository() { _uow = IoC.Get<UnitOfWork>(); } public void Save(Entity e) { _uow.Track(e); } public void SubmittChanges() { SaveInStorage(_uow.GetChanges()); } } And sometimes it is external: public class Repository { public void Save(Entity e, UnitOfWork uow) { uow.Track(e); } public void SubmittChanges(UnitOfWork uow) { SaveInStorage(uow.GetChanges()); } } Other times, is the UOW whom references the Repository public class UnitOfWork { Repository _repository; public UnitOfWork(Repository repository) { _repository = repository; } public void Save(Entity e) { this.Track(e); } public void SubmittChanges() { _repository.Save(this.GetChanges()); } } How are these two elements related? UOW tracks the elements that needs be changed, and repository contains the logic to persist those changes, but... who call who? Does the last make more sense? Also, who manages the connection? If several operations have to be done in the repository, I think using the same connection and even transaction is more sound, so maybe put the connection object inside the UOW and this one inside the repository makes sense as well. Cheers

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• Is there a decent way to maintain development of wordpress sites using the same base?

  - by Joakim Johansson

  We've been churning out wordpress sites for a while, and we'd like to keep a base repository that can be used when starting a new project, as well as updating existing sites with changes to the wordpress base. Am I wrong in assuming this would be a good thing? We take care of updating the sites, so having a common base would make this easier. I've been looking at solutions using git, such as forking a base repository and using it to pull changes to the wordpress base, but committing the site to it's own repository. Or maybe, if it's possible, storing the base as a git submodule, but this would require storing themes and plugins outside of that. Is there any common way to go about this kind of website development?

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• How much effort should you put into a junior developer?

  - by Crazy Eddie

  At what point should one give up? I've tried helping them out by having them shadow me. We agree to break a minute, and then they go missing in action for a while...then just go back to their desk. Even when I know they've done this, part of me feels like I shouldn't have to go get them but that they should be showing interest in learning. Frankly, it's a bunch of time I don't have explaining things as I go when I could just do it. Am I expecting too much to expect that if they want to learn they'll make sure I know they're ready and willing? They go to meetings that they where not told they had to, good, but then sit in the corner and sleep...bad. I don't even know what to do with that. Sometimes I give them something small to do and they do it great, so I give them something just a touch harder and they totally fail, hard. Check in things without testing them. Part of me thinks that maybe I should be spending more time with them but at the same time I don't see a lot of interest and I really, honestly don't have time teaching the same things over and over. Sometimes I get asked questions that are really, really easy to answer if you just do a little bit of your own work trying to find out. Other times I'm not asked anything. I'm sure I could be doing better but honestly...I don't really want to anymore.

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• Securing credentials passed to web service

  - by Greg Smith

  I'm attempting to design a single sign on system for use in a distributed architecture. Specifically, I must provide a way for a client website (that is, a website on a different domain/server/network) to allow users to register accounts on my central system. So, when the user takes an action on a client website, and that action is deemed to require an account, the client will produce a page (on their site/domain) where the user can register for a new account by providing an email and password. The client must then send this information to a web service, which will register the account and return some session token type value. The client will need to hash the password before sending it across the wire, and the webservice will require https, but this doesn't feel like it's safe enough and I need some advice on how I can implement this in the most secure way possible. A few other bits of relevant information: Ideally we'd prefer not to share any code with the client We've considered just redirecting the user to a secure page on the same server as the webservice, but this is likely to be rejected for non-technical reasons. We almost certainaly need to salt the password before hashing and passing it over, but that requires the client to either a) generate the salt and communicate it to us, or b) come and ask us for the salt - both feel dirty. Any help or advice is most appreciated.

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• JavaScript evolution -- weeding out the confusion [closed]

  - by good_computer

  There was JavaScript v1.3 (I guess) that we all started with. Then there was JavaScript 2.0 that Adobe implemented (ActionScript) but was abandoned later. Then came E4X. Then ES5. There is also ES harmony. I am really confused about which version is the latest and where is the standards body going. Can someone describe the whole chronology of JavaScript / ECMAScript evolution and the important differences between those versions?

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• Would a professional, self taught programmer benefit from reading an algorithms book?

  - by user65483

  I'm a 100% self taught, professional programmer (I've worked at a few web startups and made a few independent games). I've read quite a few of the "essential" books (Clean Code, The Pragmatic Programmer, Code Complete, SICP, K&R). I'm considering reading Introduction to Algorithms. I've asked a few colleagues if reading it will improve my programming skills, and I got very mixed answers. A few said yes, a few said no, and a one said "only if you spend a lot of time implementing these algorithms" (I don't). So, I figured I'd ask Stack Exchange. Is it worth the time to read about algorithms if you're a professional programmer who seldom needs to use complex algorithms? For what it's worth, I have a strong mathematical background (have a 2 year degree in Mathematics; took Linear Algebra, Differential Equations, Calc I-III).

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• How important are unit tests in software development?

  - by Lo Wai Lun

  We are doing software testing by testing a lot of I/O cases, so developers and system analysts can open reviews and test for their committed code within a given time period (e.g. 1 week). But when it come across with extracting information from a database, how to consider the cases and the corresponding methodology to start with? Although that is more likely to be a case studies because the unit-testing depends on the project we have involved which is too specific and particular most of the time. What is the general overview of the steps and precautions for unit-testing?

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• Proper way to measure the scalability of web Application

  - by Jorge

  Let's say that I have a web Application where i'm going to have 300 users and each one have to see data on real time, imagine that each client make an ajax call to the server to see in real time what's happens with the changes of the data, this calls are made each 300 ms per user. I know that i can run a simulation to see if the hardware of my server supports this example. But what happen's if the number of users start to grow up. Is there a way that i can measure the hardware needed to handle this growing behavior, a software, a formula, algorithm or maybe recommend me if i need to implement an distributed application with multiplies servers and balance the loads.

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• What is required for a scope in an injection framework?

  - by johncarl

  Working with libraries like Seam, Guice and Spring I have become accustomed to dealing with variables within a scope. These libraries give you a handful of scopes and allow you to define your own. This is a very handy pattern for dealing with variable lifecycles and dependency injection. I have been trying to identify where scoping is the proper solution, or where another solution is more appropriate (context variable, singleton, etc). I have found that if the scope lifecycle is not well defined it is very difficult and often failure prone to manage injections in this way. I have searched on this topic but have found little discussion on the pattern. Is there some good articles discussing where to use scoping and what are required/suggested prerequisites for scoping? I interested in both reference discussion or your view on what is required or suggested for a proper scope implementation. Keep in mind that I am referring to scoping as a general idea, this includes things like globally scoped singletons, request or session scoped web variable, conversation scopes, and others. Edit: Some simple background on custom scopes: Google Guice custom scope Some definitions relevant to above: “scoping” - A set of requirements that define what objects get injected at what time. A simple example of this is Thread scope, based on a ThreadLocal. This scope would inject a variable based on what thread instantiated the class. Here's an example of this: “context variable” - A repository passed from one object to another holding relevant variables. Much like scoping this is a more brute force way of accessing variables based on the calling code. Example: methodOne(Context context){ methodTwo(context); } methodTwo(Context context){ ... //same context as method one, if called from method one } “globally scoped singleton” - Following the singleton pattern, there is one object per application instance. This applies to scopes because there is a basic lifecycle to this object: there is only one of these objects instantiated. Here's an example of a JSR330 Singleton scoped object: @Singleton public void SingletonExample{ ... } usage: public class One { @Inject SingeltonExample example1; } public class Two { @Inject SingeltonExample example2; } After instantiation: one.example1 == two.example2 //true;

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• How to deal with or survive with the information overload

  - by Name

  I will better explain my question. I have been struggling with this for long time Everytime i want to read something for e,g book on java , then i find so much stuff like many tutorials , many ebooks that i am not able to decide which one to choose. I spend some time reading one , then 2 and so on and in the end i leave and gain nothing. I like the old days when we had only few resources like one hard book and at least i finish that from start to finish and gained much but now days there is so much information that mind jumps from one source to other and gain nothing what should i do

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• Solutions for software using many calls to a server

  - by Val

  I am developing software that uses many calls to a server. On a client side it's a Silverlight application. Almost every time a user clicks on a button in it, it sends 1-5 WCF calls to a server. There can be up to dozen or so users at a time. The server is a database server that serves data to a client. I am an intermediate level developer and am thinking about caching some data and syncing my changes from time to time. Are there any official solutions or technologies for it, like, patterns and such?

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• saving and retrieving a text file in java?

  - by user3319432

  import java.sql. ; import java.awt.; import javax.swing.; import java.awt.event.; public class saving extends JFrame implements ActionListener{ JTextField edpno=new JTextField(10); JLabel l0= new JLabel ("EDP Number: "); JComboBox fname = new JComboBox(); JLabel l1= new JLabel("First Name: "); JTextField lname= new JTextField(20); JLabel l2= new JLabel("Last Name: "); // JTextField contno= new JTextField(20); // JLabel l3= new JLabel("Contact Number: "); JComboBox contno = new JComboBox(); JLabel l3 = new JLabel ("Contact Number: "); JButton bOK = new JButton("Save"); JButton bRetrieve = new JButton("Retrieve"); private ImageIcon icon; JPanel C=new JPanel(){ protected void paintComponent(Graphics g){ g.drawImage(icon.getImage(),0,0,null); super.paintComponent(g); } }; public Search Record (){ icon=new ImageIcon("images/canres.png"); C.setOpaque(false); C.setLayout(new GridLayout(5,2,4,4)); setTitle("Search Record"); C.add (l0); C.add (edpno); edpno.addActionListener(this); C.add (l1); C.add (fname); fname.setForeground(Color.BLUE); fname.setFont(new Font(" ", Font.BOLD,15)); C.add (l2); C.add (lname); C.add (l3); C.add (contno); contno.setForeground(Color.BLUE); contno.setFont(new Font(" ", Font.BOLD,15)); C.add(bOK); bOK.addActionListener(this); C.add (bRetrieve); bRetrieve.addActionListener(this); bOK.setBackground(Color.white); bRetrieve.setBackground(Color.white); } public void saverecord(){ try{ //Connect to the Database Class.forName("sun.jdbc.odbc.JdbcOdbcDriver"); String path ="jdbc:odbc:;DRIVER=Microsoft Access Driver (*.mdb);DBQ=Database/roomassign.mdb"; String DBPassword =""; String DBUserName =""; Connection con = DriverManager.getConnection(path,"",""); Statement s = con.createStatement(); s.executeQuery("select firstname, Lastname, contact number from name WHERE edpno ='"+edpno.getText()+"'"); ResultSet rs = s.getResultSet(); ResultSetMetaData md = rs.getMetaData(); while(rs.next()) { fname.setSelectedItem(rs.getString(1)); lname.setText(rs.getString(2)); contno.setSelectedItem(rs.getString(3)); // crs.setSelectedItem(rs.getString(4)); } s.close(); con.close(); } catch(Exception Q) { JOptionPane.showMessageDialog(this,Q); } } public void SaveRecord(){ try{ Class.forName("sun.jdbc.odbc.JdbcOdbcDriver"); String path = "jdbc:odbc:;DRIVER=Microsoft Access Driver (*.mdb);DBQ=Database/roomassign.mdb"; String DBPassword =""; String DBUsername =""; Connection con = DriverManager.getConnection(path,"",""); Statement s = con.createStatement(); String sql = "UPDATE rooms SET Firstname='"+fname.getSelectedItem()+"',Lastname='"+lname.getText()+"',Contactnumber='"+contno.getSelectedItem()+"' WHERE '"+edpno.getText()+"'=edpno"; s.executeUpdate(sql); JOptionPane.showMessageDialog(this,"New room Record has been successfully saved"); dispose(); s.close(); con.close(); } catch(Exception Mismatch){ JOptionPane.showMessageDialog(this,Mismatch); } } public void actionPerformed (ActionEvent ako){ if (ako.getSource() == bRetrieve){ dispose(); } else if (ako.getSource() == bOK){ SaveRecord(); } } public static void main (String [] awtsave){ new Search(); } }

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• Implementing the transport layer for a SIP UAC

  - by Jonathan Henson

  I have a somewhat simple, but specific, question about implementing the transport layer for a SIP UAC. Do I expect the response to a request on the same socket that I sent the request on, or do I let the UDP or TCP listener pick up the response and then route it to the correct transaction from there? The RFC does not seem to say anything on the matter. It seems that especially using UDP, which is connection-less, that I should just let the listeners pick up the response, but that seems sort of counter intuitive. Particularly, I have seen plenty of UAC implementations which do not depend on having a Listener in the transport layer. Also, most implementations I have looked at do not have the UAS receiving loop responding on the socket at all. This would tend to indicate that the client should not be expecting a reply on the socket that it sent the request on. For clarification: Suppose my transport layer consists of the following elements: TCPClient (Sends Requests for a UAC via TCP) UDPClient (Sends Requests for a UAC vid UDP) TCPSever (Loop receiving Requests and dispatching to transaction layer via TCP) UDPServer (Loop receiving Requests and dispatching to transaction layer via UDP) Obviously, the *Client sends my Requests. The question is, what receives the Response? The *Client waiting on a recv or recvfrom call on the socket it used to send the request, or the *Server? Conversely, the *Server receives my requests, What sends the Response? The *Client? doesn't this break the roles of each member a bit?

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• "Programming error" exceptions - Is my approach sound?

  - by Medo42

  I am currently trying to improve my use of exceptions, and found the important distinction between exceptions that signify programming errors (e.g. someone passed null as argument, or called a method on an object after it was disposed) and those that signify a failure in the operation that is not the caller's fault (e.g. an I/O exception). As far as I understand, it makes little sense for an immediate caller to actually handle programming error exceptions, he should instead assure that the preconditions are met. Only "outer" exception handlers at task boundaries should catch them, so they can keep the system running if a task fails. In order to ensure that client code can cleanly catch "failure" exceptions without catching error exceptions by mistake, I create my own exception classes for all failure exceptions now, and document them in the methods that throw them. I would make them checked exceptions in Java. Now I have a few questions: Before, I tried to document all exceptions that a method could throw, but that sometimes creates an unwiedly list that needs to be documented in every method up the call chain until you can show that the error won't happen. Instead, I document the preconditions in the summary / parameter descriptions and don't even mention what happens if they are not met. The idea is that people should not try to catch these exceptions explicitly anyway, so there is no need to document their types. Would you agree that this is enough? Going further, do you think all preconditions even need to be documented for every method? For example, calling methods in IDisposable objects after calling Dispose is an error, but since IDisposable is such a widely used interface, can I just assume a programmer will know this? A similar case is with reference type parameters where passing null makes no conceivable sense: Should I document "non-null" anyway? IMO, documentation should only cover things that are not obvious, but I am not sure where "obvious" ends.

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• What sort of security method is this called (if it has a name)?

  - by loosebruce

  I have thought of a way of securing access to an application interacting with another application. Using this method Application 1 - "What is the sum of 1+1?" Application 2 - "3" Application 1 - "Access granted" Is this method used a lot, does it have a classification in the programming world? The advantages for me of using this is that I do not have to spend more effort implementing security keys/certificates. Any unauthorized machine trying to interpret it would give the correct result and identify itself as untrusted. What sort of weaknesses are there to doing this?

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• Ways to dynamically render a real world 3d environment in Unity3D

  - by Jake M

  Using Unity3D and C# I am attempting to display a 3d version of a real world location. Inside my Unity3D app, the user will specify the GPS coordinates of a location, then my app will have to generate a 3d plane(anything doesn't have to be a plane) of that location. The plane will show a 500 metre by 500 metre 3d snapshot of that location. How would you suggest I achieve this in Unity3D? What methodology would you use to achieve this? NOTE: I understand that this is a very difficult endevour(to render real world locations dynamically in Unity3d) so I expect to perform many actions to achieve this. I just don't know of all the technologies out there and which would be best for my needs For example: Suggested methodology 1: Prompt user to specify GPS coords Use Google earth API and HTTP to programmatically obtain a .khm file describing that location(Not sure if google earth provides that capability does it?) Unzip the .khm so I have the .dae file Convert that file to a .3ds file using ??? third party converter(is there a converter that exists?) Import .3ds into Unity3D at runtime as a plane(is this possible)? Suggested methodology 2: Prompt user to specify GPS coords Use Google earth API and HTTP to programmatically obtain a .khm file describing that location(Not sure if google earth provides that capability does it?) Unzip the .khm so I have the .dae file Parse .dae file using my own C# parser I will write(do you think its possible to write a .dae parser that can parse the .dae into an array of Vector3 that describe the height map of that location?) Dynamically create a plane in Unity3D and populate it with my array/list of Vector3 points(is it possible to create a plane this way?) Maybe I am meant to create a mesh instead of a plane? Can you think of any other ways I could render a real world 3d environment in Unity3D?

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• High Usage of RAM by wxPython's GUI and need some advice to reduce it

  - by user67024

  I've recently developed a GUI in wxPython for windows platform. It contains a five tabs, 4 of them are just richTextCtrl boxes and the other one has controls for uploading files, buttons, textctrls, a slider etc.. As I was new to GUI development in Python, I used wxFormBuilder to generate some of the code using a good amount of sizers. So, now the problem is that the GUI starts off with a initial memory of around 40MB which is too much for such a simple application (Or so I think) . Also, when the functions handling the functions use huge lists as the program is for debugging large data logs and identifying the problems in'em implying that I can't afford memory for GUI. So, how can I reduce that start working memory size? Is it a general issue in wxPython? And currently trying use profilers but not sure if it's going to help.

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• OOP oriented PHP app source code samples and advice

  - by abel

  The day I have been dreading has arrived. I never felt OOP or good software design was important(I knew they were important, but I thought I could manage without them.). However having read otherwise almost everywhere on the interwebs, I started dreading the day when my client would ask me for new features in an existing app. The day has come and the pain is unbearable! I have never coded my PHP websites "properly"(PHP is my primary language and the bulk of my work. I am learning Python (using web2py)) I take care that the website doesn't fall apart in a daily use scenario. I code pages like I was creating a list of static html files with bits of "magic code" in each of them(this bugs me a lot). How do I make the whole app more or less a single object? For eg. How do I design the object model for an invoicing app? I use a lot of functions for doing any particular thing in the same fashion throughout the app(for eg. validation, generating ids, calculating taxes etc.). I know the basics of OOP in general. Can anyone point me to source code samples of functional apps written in php? Or can someone provide pointers so I can recode my existing apps in a more modular way.

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