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• Why Use !boolean_variable Over boolean_variable == false

  - by ell

  A comment on this question: Calling A Method that returns a boolean value inside a conditional statement says that you should use !boolean instead of boolean == false when testing conditions. Why? To me boolean == false is much more natural in English and is more explicit. I apologise if this is just a matter of style, but I was wondering if there was some other reason for this preference of !boolean?

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• Is an 'if password == XXXXXXX' enough for minimum security?

  - by Morgan Herlocker

  If I create a login for an app that has middle to low security risk (in other words, its not a banking app or anything), is it acceptable for me to verify a password entered by the user by just saying something like: if(enteredPassword == verifiedPassword) SendToRestrictedArea(); else DisplayPasswordUnknownMessage(); It seems to easy to be effective, but I certainly would not mind if that was all that was required. Is a simple check on username/password combo enough? Update: The particular project happens to be a web service, the verification is entirely server side, and it is not open-source. Does the domain change how you would deal with this?

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• What makes signed integers behave differently?

  - by 000

  In this example of x86_64 hex/disassembled code I see: 48B80000000000000000 mov rax, 0x0 Signed Byte 52 Unsigned Byte 52 Signed Short 14388 Unsigned Short 14388 Signed Int 943863860 Unsigned Int 943863860 Signed Int64 3472328296363079732 Unsigned Int64 3472328296363079732 Float 4.630555e-05 Double 1.39804332763832e-76 String 48B80000000000000000 which to me appears to have the same functionality as: 48C7C000000000 mov rax, 0x0 48C7C000000000 Signed Byte 52 Unsigned Byte 52 Signed Short 14388 Unsigned Short 14388 Signed Int 927152180 Unsigned Int 927152180 Signed Int64 3472328377950746676 Unsigned Int64 3472328377950746676 Float 1.163599e-05 Double 1.39806836023098e-76 String 48C7C000000000 How is the first example treated differently from the second example?

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• Clients with multiple proxy and multithreading callbacks

  - by enzom83

  I created a sessionful web service using WCF, and in particular I used the NetTcpBinding binding. In addition to methods to initiate and terminate a session, other methods allow the client to send to one or more tasks to be performed (the results are returned via callback, so the service is duplex), but they also allow you to know the status of the service. Assuming you activate the same service on multiple endpoints, and assuming that the client knows these endpoints (for example, it could maintain a List of endpoints), the client should connect with one or more replicas of the same service. The client periodically updates the status of the service, so when it needs to perform a new task (the task is submitted by the user via UI), it selects the service currently less loaded and sends the task to it. Periodically, the client also initiates a maintenance procedure in order to disconnect from one or more overloaded service and in order to connect with new services. I created a client proxy using the svcutil tool. I wish each proxy can be used simultaneously by different threads, for example, in addition to the thread that submits the tasks using a proxy, there are also the following two threads which act periodically: a thread that periodically sends a request to the service in order to obtain the updated state; a thread that periodically selects a proxy to close and instantiates a new proxy to replace the closed one. To achieve these objectives, is it sufficient to create an array of proxies and manage their opening and closing in separate threads? I think I read that the proxy method calls are thread safe, so I would not need to perform a lock before requesting updates to the service. However, when the maintenance procedure (which is activated on its own thread) decides to close a proxy, should I perform a lock? Finally, each proxy is also associated with an object that implements the callback interface for the service: are the callbacks (invoked on the client) executed on different threads on the client? I would like to wrap the management of the proxy in one or more classes so that it can then easily manage within a WPF application.

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• Building a Redundant / Distrubuted Application

  - by MattW

  This is more of a "point me in the right direction" question. I (and my team of 3) have built a hosted web app that queues and routes customer chat requests to available customer service agents (It does other things as well, but this is enough background to illustrate the issue). The basic dev architecture today is: a single page ajax web UI (ASP.NET MVC) with floating chat windows (think Gmail) a backend Windows service to queue and route the chat requests this service also logs the chats, calculates service levels, etc a Comet server product that routes data between the web frontend and the backend Windows service this also helps us detect which Agents are still connected (online) And our hardware architecture today is: 2 servers to host the web UI portion of the application a load balancer to route requests to the 2 different web app servers a third server to host the SQL Server DB and the backend Windows service responsible for queuing / delivering chats So as it stands today, one of the web app servers could go down and we would be ok. However, if something would happen to the SQL Server / Windows Service server we would be boned. My question - how can I make this backend Windows service logic be able to be spread across multiple machines (distributed)? The Windows service is written to accept requests from the Comet server, check for available Agents, and route the chat to those agents. How can I make this more distributed? How can I make it so that I can distribute the work of the backend Windows service can be spread across multiple machines for redundancy and uptime purposes? Will I need to re-write it with distributed computing in mind? I should also note that I am hosting all of this on Rackspace Cloud instances - so maybe it is something I should be less concerned about? Thanks in advance for any help!

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• Inspecting the model in a Rails application

  - by Matt Sherman

  I am learning some Ruby on Rails, and am a newbie. Most of my background is in ASP.net MVC on the back end. As I play with a basic scaffold project, I wonder about this case: you jump into an established Rails project and want to get to know the model. Based on what I have seen so far (again, simple scaffold), the properties for a given class are not immediately revealed. I don't see property accessors on the model classes. I do understand that this is because of the dynamic nature of Ruby and such things are not necessary or even perhaps desirable. Convention over code, I get that. (Am familiar with dynamic concepts, mostly via JS.) But if I am somewhere off in a view, and want to quickly know whether the (eg) Person object has a MiddleName property, how would I find that out? I don't have to go into the migrations, do I?

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• What is the ideal length of a method?

  - by iPhoneDeveloper

  In object-oriented programming, there is no exact rule on the maximum length of a method , but I still found these two qutes somewhat contradicting each other, so I would like to hear what you think. In Clean Code: A Handbook of Agile Software Craftsmanship, Robert Martin says: The first rule of functions is that they should be small. The second rule of functions is that they should be smaller than that. Functions should not be 100 lines long. Functions should hardly ever be 20 lines long. and he gives an example from Java code he sees from Kent Beck: Every function in his program was just two, or three, or four lines long. Each was transparently obvious. Each told a story. And each led you to the next in a compelling order. That’s how short your functions should be! This sounds great, but on the other hand, in Code Complete, Steve McConnell says something very different: The routine should be allowed to grow organically up to 100-200 lines, decades of evidence say that routines of such length no more error prone then shorter routines. And he gives a reference to a study that says routines 65 lines or long are cheaper to develop. So while there are diverging opinions about the matter, is there a functional best-practice towards determining the ideal length of a method for you?

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• Java Alphabetize Algorithm Insertion sort vs Bubble Sort

  - by Chris Okyen

  I am supposed to "Develop a program that alphabetizes three strings. The program should allow the user to enter the three strings, and then display the strings in alphabetical order." It's instructed that I need to use the String library compareTo()/charAt()/toLowerCase() to make all the characters lowercase so the Lexicon comparison is also a alphabetical comparison. Input Pseudo Code: String input[3]; Scanner keyboard = new Scanner(System.in); System.out.println("Enter three strings: "); for(byte i = 0; i < 3; i++) input[i] = keyboard.next() The sorting would be Insertion Sort: 321 2 3 1 2 31 231 1 23 1 2 3 1 23 1 23 123 Bubble Sort 321 231 213 123 Which would be more efficient in this case? The bubble sort seems to be more efficient though they seem to have equal stats for worst best and avg case, but I read the Insertion Sort is quicker for small amounts of data like my case.

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• How would you gather client's data on Google App Engine without using Datastore/Backend Instances too much?

  - by ruslan

  I'm relatively new to StackExchange and not sure if it's appropriate place to ask design question. Site gives me a hint "The question you're asking appears subjective and is likely to be closed". Please let me know. Anyway.. One of the projects I'm working on is online survey engine. It's my first big commercial project on Google App Engine. I need your advice on how to collect stats and efficiently record them in DataStore without bankrupting me. Initial requirements are: After user finishes survey client sends list of pairs [ID (int) + PercentHit (double)]. This list shows how close answers of this user match predefined answers of reference answerers (which identified by IDs). I call them "target IDs". Creator of the survey wants to see aggregated % for given IDs for last hour, particular timeframe or from the beginning of the survey. Some surveys may have thousands of target/reference answerers. So I created entity public class HitsStatsDO implements Serializable { @Id transient private Long id; transient private Long version = (long) 0; transient private Long startDate; @Parent transient private Key parent; // fake parent which contains target id @Transient int targetId; private double avgPercent; private long hitCount; } But writing HitsStatsDO for each target from each user would give a lot of data. For instance I had a survey with 3000 targets which was answered by ~4 million people within one week with 300K people taking survey in first day. Even if we assume they were answering it evenly for 24 hours it would give us ~1040 writes/second. Obviously it hits concurrent writes limit of Datastore. I decided I'll collect data for one hour and save that, that's why there are avgPercent and hitCount in HitsStatsDO. GAE instances are stateless so I had to use dynamic backend instance. There I have something like this: // Contains stats for one hour private class Shard { ReadWriteLock lock = new ReentrantReadWriteLock(); Map<Integer, HitsStatsDO> map = new HashMap<Integer, HitsStatsDO>(); // Key is target ID public void saveToDatastore(); public void updateStats(Long startDate, Map<Integer, Double> hits); } and map with shard for current hour and previous hour (which doesn't stay here for long) private HashMap<Long, Shard> shards = new HashMap<Long, Shard>(); // Key is HitsStatsDO.startDate So once per hour I dump Shard for previous hour to Datastore. Plus I have class LifetimeStats which keeps Map<Integer, HitsStatsDO> in memcached where map-key is target ID. Also in my backend shutdown hook method I dump stats for unfinished hour to Datastore. There is only one major issue here - I have only ONE backend instance :) It raises following questions on which I'd like to hear your opinion: Can I do this without using backend instance ? What if one instance is not enough ? How can I split data between multiple dynamic backend instances? It hard because I don't know how many I have because Google creates new one as load increases. I know I can launch exact number of resident backend instances. But how many ? 2, 5, 10 ? What if I have no load at all for a week. Constantly running 10 backend instances is too expensive. What do I do with data from clients while backend instance is dead/restarting? Thank you very much in advance for your thoughts.

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• Machine Learning Web Jobs

  - by gprime

  I always see job positions for web companies for Machine Learning. For example facebook always has this type of job opening. Anyways, i was curious as to what exactly do web companies use machine learning for. Is it for giving people ads based on their site surfing history or something like that. I want to know because i have some experience with machine learning and it sounds like a fun thing to work on as long as i can convince the business guys to go ahead with it.

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• OOP concept: is it possible to update the class of an instantiated object?

  - by Federico

  I am trying to write a simple program that should allow a user to save and display sets of heterogeneous, but somehow related data. For clarity sake, I will use a representative example of vehicles. The program flow is like this: The program creates a Garage object, which is basically a class that can contain a list of vehicles objects Then the users creates Vehicles objects, these Vehicles each have a property, lets say License Plate Nr. Once created, the Vehicle object get added to a list within the Garage object --Later on--, the user can specify that a given Vehicle object is in fact a Car object or a Truck object (thus giving access to some specific attributes such as Number of seats for the Car, or Cargo weight for the truck) At first sight, this might look like an OOP textbook question involving a base class and inheritance, but the problem is more subtle because at the object creation time (and until the user decides to give more info), the computer doesn't know the exact Vehicle type. Hence my question: how would you proceed to implement this program flow? Is OOP the way to go? Just to give an initial answer, here is what I've came up until now. There is only one Vehicle class and the various properties/values are handled by the main program (not the class) through a dictionary. However, I'm pretty sure that there must be a more elegant solution (I'm developing using VB.net): Public Class Garage Public GarageAdress As String Private _ListGarageVehicles As New List(Of Vehicles) Public Sub AddVehicle(Vehicle As Vehicles) _ListGarageVehicles.Add(Vehicle) End Sub End Class Public Class Vehicles Public LicensePlateNumber As String Public Enum VehicleTypes Generic = 0 Car = 1 Truck = 2 End Enum Public VehicleType As VehicleTypes Public DictVehicleProperties As New Dictionary(Of String, String) End Class NOTE that in the example above the public/private modifiers do not necessarily reflect the original code

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• Replicate GAE Datastore On A Server LAN in Java

  - by Franz Noel

  There may be instances wherein one Company Client may not have internet connection on their vicinity. Either their Internet Service Provider currently experience a down time or there are some other problems involving the network, but not their LAN. GAE seems to be needing a connection at all times in the internet. I only need GAE Datastore. I'm thinking about a different application. Creating a Java Swing Client, for instance, and connecting to the Office Server via HRD of GAE Datastore. When I tried to check on the solutions for Java, it does not say anything about uploading all data and I do not need the App. I just need the GAE Datastore. In Java GAE, only indexes can be able to be manipulated. So, is there any tricks/ideas that you can use HRD with GAE Datastore on Java with an Internal Office Server combined? This way, it may provide service even during network down times. (Can somebody create me a tag of gae-datastore, please.)

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• OOD: All classes at bottom of hierarchy contain the same field

  - by My Head Hurts

  I am creating a class diagram for what I thought was a fairly simple problem. However, when I get to the bottom of the hierarchy, all of the classes only contain one field and it is the same one. This to me looks very wrong, but this field does not belong in any of the parent classes. I was wondering if there are any suggested design patterns in a situation like this? A simplified version of the class diagram can be found below. Note, fields named differently cannot belong to any other class +------------------+ | ObjectA | |------------------| | String one | | String two | | | +---------+--------+ | +---------------+----------------+ | | +--------|--------+ +--------|--------+ | ObjectAA | | ObjectAB | |-----------------| |-----------------| | String three | | String four | | | | | +--------+--------+ +--------+--------+ | | | | +--------|--------+ +--------|--------+ | ObjectAAA | | ObjectABA | |-----------------| |-----------------| | String five | | String five | | | | | +-----------------+ +-----------------+ ASCII tables drawn using http://www.asciiflow.com/

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• Is It Worth It To Learn Experimental Languages

  - by Xander Lamkins

  I'm a young programmer who desires to work in the field someday as a programmer. I know Java, VB.NET and C#. I want to learn a new language (as I programmer, I know that it is valuable to extend what I know - to learn languages that make you think differently). I took a look online to see what languages were common. Everybody knows C and C++ (even those muggles who know so little about computers in general), so I thought, maybe I should push for C. C and C++ are nice but they are old. Things like Haskell and Forth (etc. etc. etc.) are old and have lost their popularity. I'm scared of learning C (or even C++) for this same reason. Java is pretty old as well and is slow because it's run by the JVM and not compiled to native code. I've been a Windows developer for quite a while. I recently started using Java - but only because it was more versatile and spreadable to other places. The problem is that it doesn't look like a very usable language for these reasons: It's most used purpose is for web application and cellphone apps (specifically Android) As far as actual products made with it, the only things that come to mind are Netbeans, Eclipse (hurrah for making and IDE with the language the IDE is for - it's like making a webpage for writing HTML/CSS/Javascript), and Minecraft which happens to be fun but laggy and bipolar as far as computer spec. support. Other than that it's used for servers but heck - I don't only want to make/configure servers. The .NET languages are nice, however: People laugh if I even mention VB.NET or C# in a serious conversation. It isn't cross-platform unless you use MONO (which is still in development and has some improvements to be made). Lacks low level stuff because, like Java with the JVM, it is run/managed by the CLR. My first thought was learning something like C and then using it to springboard into C++ (just to make sure I would have a strong understanding/base), but like I said earlier, it's getting older and older by the minute. What I've Looked Into Fantom looks nice. It's like a nice middleman between my two favorite languages and even lets me publish between the two interchangeably, but, unlike what I want, it compiles to the CLR or JVM (depending on what you publish it to) instead of it being a complete compile. D also looks nice. It seems like a very usable language and from multiple sources it appears to actually be better than C/C++. I would jump right with it, but I'm still unsure of its success because it obviously isn't very mainstream at this point. There are a couple others that looked pretty nice that focused on other things such as Opa with web development and Go by GOOGLE. My Question Is it worth learning these "experimental" languages? I've read other questions that say that if you aren't constantly learning languages and open to all languages that you aren't in the right mindset for programming. I understand this and I still might not quite be getting it, but in truth, if a language isn't going to become mainstream, should I spend my time learning something else? I don't want to learn old (or any going to soon be old) programming languages. I know that many people see this as something important, *but would any of you ever actually consider (assuming you didn't already know) FORTRAN? My goal is to stay current to make sure I'm successful in the future. Disclaimer Yes, I am a young programmer, so I probably made a lot of naive statements in my question. Feel free to correct me on ANYTHING! I have to start learning somewhere so I'm sure a lot of my knowledge is sketchy enough to have caused to incorrect statements or flaws in my thinking. Please leave any feelings you have in the comments.

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• Something confusing about Single Responsibility Principle

  - by user1483278

  1) In fact if two responsibilities are always expected to change at the same time you arguably should not separate them into different classes as this would lead, to quote Martin, to a "smell of Needless Complexity". The same is the case for responsibilities that never change - the behavior is invariant, and there is no need to split it. I assume even if non-related responsibilities are always expected to change for the same reason ( or if they never change ), we still shouldn't put them in the same class, since this would still violate high cohesion principle? 2) I've found two quite different definitions for SRP: Single Responsibility Principle says that a subsystem, module, class, or even a function, should not have more than one reason to change. and There should never be more than one reason for a class to change Doesn't the latter definition narrow SRP to a class level? If so, isn't first quote wrong by claiming that SRP can also be applied at subsystem, module and function levels? thank you

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• Best practice while marking a bug as resolved with Bugzilla (versioning of product and components)

  - by Vincent B.

  I am wondering what is the best way to handle the situation of marking a bug as resolved and providing a version of component/product in which this fix can be found. Context For a project I am working on, we are using Bugzilla for issue tracking, and we have the following: A product "A" with a version number like vA.B.C.D, This product "A" have the following components: Component "C1" with a version number like vA.B.C.D, Component "C2" with a version number like vA.B.C.D, Component "C3" with a version number like vA.B.C.D. Internally we keep track of which component versions have been used to generate the product A version vA.B.C.D. Example: Product "A" version v1.0.0.0 has been produced from component "C1" v1.0.0.3, component "C2" v1.3.0.0 and component "C3" v2.1.3.5. And Product "A" version v1.0.1.0 has been produced from component "C1" v1.0.0.4, component "C2" v1.3.0.0 and component "C3" v2.1.3.5. Each component is a SVN repository. The person in charge of generating the product "A" have only access to the different components tags folder in SVN, and not the trunk of each component repository. Problem Now the problem is the following, when a bug is found in the product "A", and that the bug is related to Component "C1", the version of product "A" is chosen (e.g. v1.0.0.0), and this version allow the developer to know which version of component "C1" has the bug (here it will be v1.0.0.3). A bug report is created. Now let's say that the developer responsible for component "C1" corrects the bug, then when the bug seems to be fixed and after some test and validation, the developer generates a new tag for component "C1", with the version v1.0.0.4. At this time, the developer of component "C1" needs to update the bug report, but what is the best to do: Mark the bug as resolved/fixed and add a comment saying "This bug has been fixed in the tags v1.0.0.4 of C1 component" ? Keep the bug as assigned, add a comment saying "This bug has been fixed in the tags v1.0.0.4 of C1 component, update this bug status to resolved for the next version of the product that will be generated with the newest version (v1.0.0.4 of C1)" ? Another possible way to deal with this problem. Right now the problem is that when a product component CX is fixed, it is not sure in which future version of the product A it will be included, so it is for me not possible to say in which version of the product it will be solved, but it is possible to say in which version of the Component CX it has been solved. So when do we need to mark a bug as solved, when the product A version include the fixed version of CX, or only when CX component has been fixed ? Thanks for your personal feedback and ideas about this !

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• Efficient Trie implementation for unicode strings

  - by U Mad

  I have been looking for an efficient String trie implementation. Mostly I have found code like this: Referential implementation in Java (per wikipedia) I dislike these implementations for mostly two reasons: They support only 256 ASCII characters. I need to cover things like cyrillic. They are extremely memory inefficient. Each node contains an array of 256 references, which is 4096 bytes on a 64 bit machine in Java. Each of these nodes can have up to 256 subnodes with 4096 bytes of references each. So a full Trie for every ASCII 2 character string would require a bit over 1MB. Three character strings? 256MB just for arrays in nodes. And so on. Of course I don't intend to have all of 16 million three character strings in my Trie, so a lot of space is just wasted. Most of these arrays are just null references as their capacity far exceeds the actual number of inserted keys. And if I add unicode, the arrays get even larger (char has 64k values instead of 256 in Java). Is there any hope of making an efficient trie for strings? I have considered a couple of improvements over these types of implementations: Instead of using array of references, I could use an array of primitive integer type, which indexes into an array of references to nodes whose size is close to the number of actual nodes. I could break strings into 4 bit parts which would allow for node arrays of size 16 at the cost of a deeper tree.

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• When do you use a struct instead of a class?

  - by jkohlhepp

  What are your rules of thumb for when to use structs vs. classes? I'm thinking of the C# definition of those terms but if your language has similar concepts I'd like to hear your opinion as well. I tend to use classes for almost everything, and use structs only when something is very simplistic and should be a value type, such as a PhoneNumber or something like that. But this seems like a relatively minor use and I hope there are more interesting use cases.

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• What is the convention for the star location in reference variables?

  - by Brett Ryan

  Have been learning Objective-C and different books and examples use differing conventions for the location of the star (*) when naming reference variables. MyType* x; MyType *y; MyType*z; // this also works Personally I prefer the first option as it illustrates that x is a "pointer type of MyType". I see the first two used interchangeably, and sometimes in the same code I've seen differing uses of both. I want to know what is the most common convention It's been a very long time since I've programmed in C (15 years) so I can't remember if all variants are legal for C also or if this is Objective-C specific. I'd prefer answers which state why one is better than the other, as how I explained how I read it above.

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• Do you think asking to sign contributor license agreement for a open source project creates a resistance for contributors?

  - by Appu

  I am working on a open-source project which is backed by an organization. Organization pays a team to make this open-source project. This project will be licensed with GPLv3. We are debating on having a CLA for contributors. Do you think mandating a CLA will reduce the number of contributors? I have observed that people have no issues in signing a CLA when the project is really popular. So do you think CLA will create a resistance to contribute?

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• Immutable Method Java

  - by Chris Okyen

  In Java, there is the final keyword in lieu of the const keyword in c and c++. In the latter languages their is mutable and immutable methods such as stated in one answer by Johannes Schaub - litb the question how-many-and-which-are-the-uses-of-const-in-ce Use const to tell others methods won't change the logical state of this object. struct SmartPtr { int getCopies() const { return mCopiesMade; } }ptr1; ... int var = ptr.getCopies(); // returns mCopiesMade and is specified that to not modify objects state. How is this performed in Java?

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• Quality Assurance activities

  - by MasloIed

  Having asked but deleted the question as it was a bit misunderstood. If Quality Control is the actual testing, what are the commonest true quality assurance activities? I have read that verification (reviews, inspections..) but it does not make much sense to me as it looks more like quality control as mentioned here: DEPARTMENT OF HEALTH AND HUMAN SERVICES ENTERPRISE PERFORMANCE LIFE CYCLE FRAMEWORK Practices guide Verification - “Are we building the product right?” Verification is a quality control technique that is used to evaluate the system or its components to determine whether or not the project’s products satisfy defined requirements. During verification, the project’s processes are reviewed and examined by members of the IV&V team with the goal of preventing omissions, spotting problems, and ensuring the product is being developed correctly. Some Verification activities may include items such as: • Verification of requirement against defined specifications • Verification of design against defined specifications • Verification of product code against defined standards • Verification of terms, conditions, payment, etc., against contracts

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• What to do when issue-tracker is down?

  - by Pablo

  It has happened in our team that our issue-tracker is down. Happens about once a week now (yes, wow), and there's not really much we can do to get it back up, since it's hosted by our client in a different timezone. It sometimes takes several hours for it to be operative again. In the meanwhile, we can't really tell which issues we were working on, and in case we do, we cannot update those issues, as in moving them through the workflow, logging used hours, checking the issue's description, leaving comments, and so on. So the question is: how can we, as a team, work in the meanwhile so that when the issue-tracker is up again, we have the least possible hassle updating it with what we've been working?

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• Materialized View does not import properly when importing on a second instance of a database

  - by marinus

  When I import a database with materialized view mv_mt in just one database (Oracle) everything is ok. create materialized view mv_mt refresh complete next trunc( sysdate ) + 1 as SELECT sysdate, media_type.* from media_type; But when I try to import the same database to a copy in another schema I get the following errors: IMP-00017: following statement failed with ORACLE error 1: "BEGIN DBMS_JOB.ISUBMIT(JOB=438,WHAT='dbms_refresh.refresh(''"ALEXANDRA"" "."MV_MT"'');',NEXT_DATE=TO_DATE('2012-07-02:14:22:36','YYYY-MM-DD:HH24:MI:" "SS'),INTERVAL='sysdate + 1 / 24 / 60 / 6 ',NO_PARSE=TRUE); END;" IMP-00003: ORACLE error 1 encountered ORA-00001: unique constraint (SYS.I_JOB_JOB) violated ORA-06512: at "SYS.DBMS_JOB", line 100 ORA-06512: at line 1 IMP-00017: following statement failed with ORACLE error 23421: "BEGIN dbms_refresh.make('"ALEXANDRA"."MV_MT"',list=null,next_date=null," "interval=null,implicit_destroy=TRUE,lax=FALSE,job=438,rollback_seg=NUL" "L,push_deferred_rpc=TRUE,refresh_after_errors=FALSE,purge_option = 1,par" "allelism = 0,heap_size = 0); END;" IMP-00003: ORACLE error 23421 encountered ORA-23421: job number 438 is not a job in the job queue ORA-06512: at "SYS.DBMS_SYS_ERROR", line 86 ORA-06512: at "SYS.DBMS_IJOB", line 793 ORA-06512: at "SYS.DBMS_REFRESH", line 86 ORA-06512: at "SYS.DBMS_REFRESH", line 62 ORA-06512: at line 1 IMP-00017: following statement failed with ORACLE error 23410: "BEGIN dbms_refresh.add(name='"ALEXANDRA"."MV_MT"',list='"ALEXANDRA"."MV" "_MT"',siteid=0,export_db='ORCL01'); END;" IMP-00003: ORACLE error 23410 encountered ORA-23410: materialized view "ALEXANDRA"."MV_MT" is already in a refresh group ORA-06512: at "SYS.DBMS_SYS_ERROR", line 95 ORA-06512: at "SYS.DBMS_IREFRESH", line 484 ORA-06512: at "SYS.DBMS_REFRESH", line 140 ORA-06512: at "SYS.DBMS_REFRESH", line 125 ORA-06512: at line 1 Anyone any ideas? Regards, Marinus

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• How I use RegExp in my Java program? [migrated]

  - by MIH1406

  I have the following string examples: 00001 1 12 123 00002 3 7 321 00003 99 23 332 00004 192 50 912 In a separate text file. Numbers are separated by tabs not spaces. I tried to read the file and print each line if it matches a given RegExp, but I could not find the suitable RegExp for these lines. private static void readFile() { String fileName = "processes.lst"; FileReader file = null; String result = ""; try { file = new FileReader(fileName); BufferedReader reader = new BufferedReader(file); String line = null; String regEx = "[0-9]\t[0-9]\t[0-9]\t[0-9]"; while((line = reader.readLine()) != null) { if(line.matches(regEx)) { result += "\n" + line; } } } catch(Exception e) { System.out.println(e.getMessage()); } finally { if(file != null) try { file.close(); } catch(Exception e) { System.out.println(e.getMessage()); } } System.out.println(result); } I ended up without any string being printed!!

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