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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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• MySql query optimization help

  - by rohitgu

  I have few queries and am not able to figure out how to optimize them, QUERY 1 select * from t_twitter_tracking where classified is null and tweetType='ENGLISH' order by id limit 500; QUERY 2 Select count(*) as cnt, DATE_FORMAT(CONVERT_TZ(wrdTrk.createdOnGMTDate,'+00:00','+05:30'),'%Y-%m-%d') as dat from t_twitter_tracking wrdTrk where wrdTrk.word like ('dell') and CONVERT_TZ(wrdTrk.createdOnGMTDate,'+00:00','+05:30') between '2010-12-12 00:00:00' and '2010-12-26 00:00:00' group by dat; Both these queries run on the same table, CREATE TABLE `t_twitter_tracking` ( `id` BIGINT(20) NOT NULL AUTO_INCREMENT, `word` VARCHAR(200) NOT NULL, `tweetId` BIGINT(100) NOT NULL, `twtText` VARCHAR(800) NULL DEFAULT NULL, `language` TEXT NULL, `links` TEXT NULL, `tweetType` VARCHAR(20) NULL DEFAULT NULL, `source` TEXT NULL, `sourceStripped` TEXT NULL, `isTruncated` VARCHAR(40) NULL DEFAULT NULL, `inReplyToStatusId` BIGINT(30) NULL DEFAULT NULL, `inReplyToUserId` INT(11) NULL DEFAULT NULL, `rtUsrProfilePicUrl` TEXT NULL, `isFavorited` VARCHAR(40) NULL DEFAULT NULL, `inReplyToScreenName` VARCHAR(40) NULL DEFAULT NULL, `latitude` BIGINT(100) NOT NULL, `longitude` BIGINT(100) NOT NULL, `retweetedStatus` VARCHAR(40) NULL DEFAULT NULL, `statusInReplyToStatusId` BIGINT(100) NOT NULL, `statusInReplyToUserId` BIGINT(100) NOT NULL, `statusFavorited` VARCHAR(40) NULL DEFAULT NULL, `statusInReplyToScreenName` TEXT NULL, `screenName` TEXT NULL, `profilePicUrl` TEXT NULL, `twitterId` BIGINT(100) NOT NULL, `name` TEXT NULL, `location` VARCHAR(100) NULL DEFAULT NULL, `bio` TEXT NULL, `url` TEXT NULL COLLATE 'latin1_swedish_ci', `utcOffset` INT(11) NULL DEFAULT NULL, `timeZone` VARCHAR(100) NULL DEFAULT NULL, `frenCnt` BIGINT(20) NULL DEFAULT '0', `createdAt` DATETIME NULL DEFAULT NULL, `createdOnGMT` VARCHAR(40) NULL DEFAULT NULL, `createdOnServerTime` DATETIME NULL DEFAULT NULL, `follCnt` BIGINT(20) NULL DEFAULT '0', `favCnt` BIGINT(20) NULL DEFAULT '0', `totStatusCnt` BIGINT(20) NULL DEFAULT NULL, `usrCrtDate` VARCHAR(200) NULL DEFAULT NULL, `humanSentiment` VARCHAR(30) NULL DEFAULT NULL, `replied` BIT(1) NULL DEFAULT NULL, `replyMsg` TEXT NULL, `classified` INT(32) NULL DEFAULT NULL, `createdOnGMTDate` DATETIME NULL DEFAULT NULL, `locationDetail` TEXT NULL, `geonameid` INT(11) NULL DEFAULT NULL, `country` VARCHAR(255) NULL DEFAULT NULL, `continent` CHAR(2) NULL DEFAULT NULL, `placeLongitude` FLOAT NULL DEFAULT NULL, `placeLatitude` FLOAT NULL DEFAULT NULL, PRIMARY KEY (`id`), INDEX `id` (`id`, `word`), INDEX `createdOnGMT_index` (`createdOnGMT`) USING BTREE, INDEX `word_index` (`word`) USING BTREE, INDEX `location_index` (`location`) USING BTREE, INDEX `classified_index` (`classified`) USING BTREE, INDEX `tweetType_index` (`tweetType`) USING BTREE, INDEX `getunclassified_index` (`classified`, `tweetType`) USING BTREE, INDEX `timeline_index` (`word`, `createdOnGMTDate`, `classified`) USING BTREE, INDEX `createdOnGMTDate_index` (`createdOnGMTDate`) USING BTREE, INDEX `locdetail_index` (`country`, `id`) USING BTREE, FULLTEXT INDEX `twtText_index` (`twtText`) ) COLLATE='utf8_general_ci' ENGINE=MyISAM ROW_FORMAT=DEFAULT AUTO_INCREMENT=12608048; The table has more than 10 million records. How can I optimize it?

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• Why "object reference not set to an instance of an object" doesn't tell us which object?

  - by Saeed Neamati

  We're launching a system, and we sometimes get the famous exception NullReferenceException with the message Object reference not set to an instance of an object. However, in a method where we have almost 20 objects, having a log which says an object is null, is really of no use at all. It's like telling you, when you are the security agent of a seminar, that a man among 100 attendees is a terrorist. That's really of no use to you at all. You should get more information, if you want to detect which man is the threatening man. Likewise, if we want to remove the bug, we do need to know which object is null. Now, something has obsessed my mind for several months, and that is: Why .NET doesn't give us the name, or at least the type of the object reference, which is null?. Can't it understand the type from reflection or any other source? Also, what are the best practices to understand which object is null? Should we always test nullability of objects in these contexts manually and log the result? Is there a better way?

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• PHP: why is this null different from the other null

  - by matthy

  hi i tried 2 things what should be the same however it my testing says different does anyone know why the only thing i do is put it in a variable... if ($_SESSION[$something] === null) echo("this is null"); $_SESSION[$something] does not exists so it indeed says: "this is null". now look at this $theSession = $_SESSION[$something]; if (theSession === null) echo("this is null"); now it does not say "this is null" while it should be exactly the same right?

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• "Null" is null or not an object error in IE javascript

  - by user89691

  The following code executes fine in Firefox and Chrome, but gives an error: 'null' is null or not an object when executed in Internet Explorer. if (xmlhttp.responseXML != null) { var xmlDoc = xmlhttp.responseXML.documentElement ; var ResultNodes = xmlDoc.getElementsByTagName ("Result") ; <---- error here if (ResultNodes != null) { (I would have thought the line after the one indicated would be more likely to return the error but the debugger says the run-time error is at the line indicated) Any ideas why?

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• "Null" is null or not an object error in IE javascript

  - by rossmcm

  The following code executes fine in Firefox and Chrome, but gives an error: 'null' is null or not an object when executed in Internet Explorer. if (xmlhttp.responseXML != null) { var xmlDoc = xmlhttp.responseXML.documentElement ; var ResultNodes = xmlDoc.getElementsByTagName ("Result") ; <---- error here if (ResultNodes != null) { (I would have thought the line after the one indicated would be more likely to return the error but the debugger says the run-time error is at the line indicated) Any ideas why?

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• Returning null vs Throwing exceptions

  - by Svish

  Is in a bit of disagreement with a more experienced developer on this issue, and was wondering what you guys here think about this. Environment is Java, EJB 3, services, etc. The code I wrote calls a service to get things and to create things. Problem was that I got null pointer exceptions in places that didn't make sense. For example when I asked the service to create an object, I got null back. And when I tried to look up an object with an id I knew existed, I still got null back. Was like it was ignoring me. Spent some time trying to figure out what was wrong in my code (since I'm less experienced I usually assume I have messed up). Turns out the reason was security. If the user principal using my service didn't have the right permissions to use the service I called from my service, then that service simply returned null. The services that are here already are usually not documented either, so this is just something you have to know... somehow... So here is the thing: I mean that this is rather confusing as a developer interacting with this service. To me it would make much more sense if that service thew an exception which would tell me that hey, you don't have the proper permissions to get info about this thing or to create this new thing. I would then immediately know why my service wasn't working as expected. However, he argued that asking is not wrong. Exceptions should only be thrown when there is an error and asking for a thing is not an error. Even if you don't have permission to "see" that the thing you asked for. The things are often looked up in a GUI by users and for those users not having the right permissions, these things simply "do not exist". So, in short: Asking is not wrong, hence no exception. Get methods return null because to those users those things "doesn't exist". Create methods return null because nothing was created, since the user wasn't allowed to create anything. So, what do you guys think? Is this normal and/or good practice? I prefer exceptions as I prefer throwing and catching exceptions because I find it much easier to know what's going on. So I would for example also prefer to throw a NotFoundException if you asked for an id which didn't exist, rather than returning null. Anyways, just curious to what others think about this as I'm not the most experienced developer yet.

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• Is DataAdapter use facade pattern or Adapter pattern.

  - by Krirk

  When i see Update(),Fill() method of DataAdapter object I always think Is DataAdapter use facade pattern ? It looks like behind the scenes It will create Command object, Connection object and execute it for us. Or DataAdapter use Adapter pattern because it is adapter between Dataset and Comamand object ,Connection object ?

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• #define NULL NULL

  - by sheepsimulator

  #ifndef NULL #define NULL NULL #endif This code compiles in gcc with no warnings/errors. Can someone explain what the preprocessor is doing here?

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• which is more effective [ if(NULL==variables) or if(variables==NULL) ]

  - by Apache

  hi expert, want to ask, in java if(NULL==variables) or if(variables==NULL) which will be more effective and what are the difference, thanks

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• Generic object to object mapping with parametrized constructor

  - by Rody van Sambeek

  I have a data access layer which returns an IDataRecord. I have a WCF service that serves DataContracts (dto's). These DataContracts are initiated by a parametrized constructor containing the IDataRecord as follows: [DataContract] public class DataContractItem { [DataMember] public int ID; [DataMember] public string Title; public DataContractItem(IDataRecord record) { this.ID = Convert.ToInt32(record["ID"]); this.Title = record["title"].ToString(); } } Unfortanately I can't change the DAL, so I'm obliged to work with the IDataRecord as input. But in generat this works very well. The mappings are pretty simple most of the time, sometimes they are a bit more complex, but no rocket science. However, now I'd like to be able to use generics to instantiate the different DataContracts to simplify the WCF service methods. I want to be able to do something like: public T DoSomething<T>(IDataRecord record) { ... return new T(record); } So I'd tried to following solutions: Use a generic typed interface with a constructor. doesn't work: ofcourse we can't define a constructor in an interface Use a static method to instantiate the DataContract and create a typed interface containing this static method. doesn't work: ofcourse we can't define a static method in an interface Use a generic typed interface containing the new() constraint doesn't work: new() constraint cannot contain a parameter (the IDataRecord) Using a factory object to perform the mapping based on the DataContract Type. does work, but: not very clean, because I now have a switch statement with all mappings in one file. I can't find a real clean solution for this. Can somebody shed a light on this for me? The project is too small for any complex mapping techniques and too large for a "switch-based" factory implementation.

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• MySQL Database Query Problem

  - by moustafa

  I need your help!!!. I need to query a table in my database that has record of goods sold. I want the query to detect a particular product and also calculate the quantity sold. The product are 300 now, but it would increase in the future. Below is a sample of my DB Table #---------------------------- # Table structure for litorder #---------------------------- CREATE TABLE `litorder` ( `id` int(10) NOT NULL auto_increment, `name` varchar(50) NOT NULL default '', `address` varchar(50) NOT NULL default '', `xdate` date NOT NULL default '0000-00-00', `ref` varchar(20) NOT NULL default '', `code1` varchar(50) NOT NULL default '', `code2` varchar(50) NOT NULL default '', `code3` varchar(50) NOT NULL default '', `code4` varchar(50) NOT NULL default '', `code5` varchar(50) NOT NULL default '', `code6` varchar(50) NOT NULL default '', `code7` varchar(50) NOT NULL default '', `code8` varchar(50) NOT NULL default '', `code9` varchar(50) NOT NULL default '', `code10` varchar(50) NOT NULL default '', `code11` varchar(50) character set latin1 collate latin1_bin NOT NULL default '', `code12` varchar(50) NOT NULL default '', `code13` varchar(50) NOT NULL default '', `code14` varchar(50) NOT NULL default '', `code15` varchar(50) NOT NULL default '', `product1` varchar(100) NOT NULL default '0', `product2` varchar(100) NOT NULL default '0', `product3` varchar(100) NOT NULL default '0', `product4` varchar(100) NOT NULL default '0', `product5` varchar(100) NOT NULL default '0', `product6` varchar(100) NOT NULL default '0', `product7` varchar(100) NOT NULL default '0', `product8` varchar(100) NOT NULL default '0', `product9` varchar(100) NOT NULL default '0', `product10` varchar(100) NOT NULL default '0', `product11` varchar(100) NOT NULL default '0', `product12` varchar(100) NOT NULL default '0', `product13` varchar(100) NOT NULL default '0', `product14` varchar(100) NOT NULL default '0', `product15` varchar(100) NOT NULL default '0', `price1` int(10) NOT NULL default '0', `price2` int(10) NOT NULL default '0', `price3` int(10) NOT NULL default '0', `price4` int(10) NOT NULL default '0', `price5` int(10) NOT NULL default '0', `price6` int(10) NOT NULL default '0', `price7` int(10) NOT NULL default '0', `price8` int(10) NOT NULL default '0', `price9` int(10) NOT NULL default '0', `price10` int(10) NOT NULL default '0', `price11` int(10) NOT NULL default '0', `price12` int(10) NOT NULL default '0', `price13` int(10) NOT NULL default '0', `price14` int(10) NOT NULL default '0', `price15` int(10) NOT NULL default '0', `quantity1` int(10) NOT NULL default '0', `quantity2` int(10) NOT NULL default '0', `quantity3` int(10) NOT NULL default '0', `quantity4` int(10) NOT NULL default '0', `quantity5` int(10) NOT NULL default '0', `quantity6` int(10) NOT NULL default '0', `quantity7` int(10) NOT NULL default '0', `quantity8` int(10) NOT NULL default '0', `quantity9` int(10) NOT NULL default '0', `quantity10` int(10) NOT NULL default '0', `quantity11` int(10) NOT NULL default '0', `quantity12` int(10) NOT NULL default '0', `quantity13` int(10) NOT NULL default '0', `quantity14` int(10) NOT NULL default '0', `quantity15` int(10) NOT NULL default '0', `amount1` int(10) NOT NULL default '0', `amount2` int(10) NOT NULL default '0', `amount3` int(10) NOT NULL default '0', `amount4` int(10) NOT NULL default '0', `amount5` int(10) NOT NULL default '0', `amount6` int(10) NOT NULL default '0', `amount7` int(10) NOT NULL default '0', `amount8` int(10) NOT NULL default '0', `amount9` int(10) NOT NULL default '0', `amount10` int(10) NOT NULL default '0', `amount11` int(10) NOT NULL default '0', `amount12` int(10) NOT NULL default '0', `amount13` int(10) NOT NULL default '0', `amount14` int(10) NOT NULL default '0', `amount15` int(10) NOT NULL default '0', `totalNaira` double(20,0) NOT NULL default '0', `totalDollar` int(20) NOT NULL default '0', PRIMARY KEY (`id`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 COMMENT='InnoDB free: 4096 kB; InnoDB free: 4096 kB; InnoDB free: 409'; #---------------------------- # Records for table litorder #---------------------------- insert into litorder values (27, 'Sanyaolu Fisayo', '14 Adegboyega Street Palmgrove Lagos', '2010-05-31', '', 'DL 001', 'DL 002', 'DL 003', '', '', '', '', '', '', '', '', '', '', '', '', 'AILMENT & PREVENTION DVD- ENGLISH', 'AILMENT & PREVENTION DVD- HAUSA', 'BEAUTY CD', '', '', '', '', '', '', '', '', '', '', '', '', 800, 800, 3000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 16, 16, 20, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 12800, 12800, 60000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, '85600', 563), (28, 'Irenonse Esther', 'Lagos,Nigeria', '2010-06-01', '', 'DL 005', 'DL 008', 'FC 004', '', '', '', '', '', '', '', '', '', '', '', '', 'GET HEALTHY DVD', 'YOUR FUTURE DVD', 'FOREVER FACE CAP (YELLOW)', '', '', '', '', '', '', '', '', '', '', '', '', 1000, 900, 2000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 2, 3, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2000, 1800, 6000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, '9800', 64), (29, 'Kalu Lekway', 'Lagos, Nigeria', '2010-06-01', '', 'DL 001', 'DL 003', '', '', '', '', '', '', '', '', '', '', '', '', '', 'AILMENT & PREVENTION DVD- ENGLISH', 'BEAUTY CD', '', '', '', '', '', '', '', '', '', '', '', '', '', 800, 3000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 3, 6, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2400, 18000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, '20400', 133), (30, 'Dele', 'Ilupeju', '2010-06-02', '', 'DL 001', 'DL 003', '', '', '', '', '', '', '', '', '', '', '', '', '', 'AILMENT & PREVENTION DVD- ENGLISH', 'BEAUTY CD', '', '', '', '', '', '', '', '', '', '', '', '', '', 800, 3000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 10, 10, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 8000, 30000, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, '38000', 250);

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• What are the disadvantages of self-encapsulation?

  - by Dave Jarvis

  Background Tony Hoare's billion dollar mistake was the invention of null. Subsequently, a lot of code has become riddled with null pointer exceptions (segfaults) when software developers try to use (dereference) uninitialized variables. In 1989, Wirfs-Brock and Wikerson wrote: Direct references to variables severely limit the ability of programmers to re?ne existing classes. The programming conventions described here structure the use of variables to promote reusable designs. We encourage users of all object-oriented languages to follow these conventions. Additionally, we strongly urge designers of object-oriented languages to consider the effects of unrestricted variable references on reusability. Problem A lot of software, especially in Java, but likely in C# and C++, often uses the following pattern: public class SomeClass { private String someAttribute; public SomeClass() { this.someAttribute = "Some Value"; } public void someMethod() { if( this.someAttribute.equals( "Some Value" ) ) { // do something... } } public void setAttribute( String s ) { this.someAttribute = s; } public String getAttribute() { return this.someAttribute; } } Sometimes a band-aid solution is used by checking for null throughout the code base: public void someMethod() { assert this.someAttribute != null; if( this.someAttribute.equals( "Some Value" ) ) { // do something... } } public void anotherMethod() { assert this.someAttribute != null; if( this.someAttribute.equals( "Some Default Value" ) ) { // do something... } } The band-aid does not always avoid the null pointer problem: a race condition exists. The race condition is mitigated using: public void anotherMethod() { String someAttribute = this.someAttribute; assert someAttribute != null; if( someAttribute.equals( "Some Default Value" ) ) { // do something... } } Yet that requires two statements (assignment to local copy and check for null) every time a class-scoped variable is used to ensure it is valid. Self-Encapsulation Ken Auer's Reusability Through Self-Encapsulation (Pattern Languages of Program Design, Addison Wesley, New York, pp. 505-516, 1994) advocated self-encapsulation combined with lazy initialization. The result, in Java, would resemble: public class SomeClass { private String someAttribute; public SomeClass() { setAttribute( "Some Value" ); } public void someMethod() { if( getAttribute().equals( "Some Value" ) ) { // do something... } } public void setAttribute( String s ) { this.someAttribute = s; } public String getAttribute() { String someAttribute = this.someAttribute; if( someAttribute == null ) { setAttribute( createDefaultValue() ); } return someAttribute; } protected String createDefaultValue() { return "Some Default Value"; } } All duplicate checks for null are superfluous: getAttribute() ensures the value is never null at a single location within the containing class. Efficiency arguments should be fairly moot -- modern compilers and virtual machines can inline the code when possible. As long as variables are never referenced directly, this also allows for proper application of the Open-Closed Principle. Question What are the disadvantages of self-encapsulation, if any? (Ideally, I would like to see references to studies that contrast the robustness of similarly complex systems that use and don't use self-encapsulation, as this strikes me as a fairly straightforward testable hypothesis.)

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• When modeling a virtual circuit board, what is the best design pattern to check for cycles?

  - by Wallace Brown

  To make it simple assume you have only AND and OR gates. Each has two inputs and one output. The output of two inputs can be used as an input for the next gate For example: A AND B - E C AND D - F E OR F - G Assuming an arbitrary number of gates, we want to check if the circuit ever connects back into itself at an earlier state? For example: E AND F - A This should be illegal since it creates an endless cycle. What design pattern would best be able to check for these cycles?

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• would a composite design pattern be useful for group membership?

  - by changokun

  I'm trying to think about the best way to handle group memberships on a website. People sign up and select checkboxes in a list of interests. Every week we send out interest-themed emails to those members that indicated that interest. however i store the information in the database, while i am working with the lists and generating lists of email addresses or manipulating group memberships, the composite design pattern looked interesting. it would be easy to populate the group, then do some aggregating functions that say... generate the list of email addresses based on the interests. but i'm not sure i'm seeing any other advantages. i do need something scalable, and flexible. thoughts?

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• null coalescing operator for javascript?

  - by Daniel Schaffer

  I assumed this question has already been asked here, but I couldn't find any, so here it goes: Is there a null coalescing operator in Javascript? For example, in C#, I can do this: String someString = null; var whatIWant = someString ?? "Cookies!"; The best approximation I can figure out for Javascript is using the conditional operator: var someString = null; var whatIWant = someString ? someString : 'Cookies!'; Which is sorta icky IMHO. Can I do better?

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• Design pattern for cost calculator app?

  - by Anders Svensson

  Hi, I have a problem that I’ve tried to get help for before, but I wasn’t able to solve it then, so I’m trying to simplify the problem now to see if I can get some more concrete help with this because it is driving me crazy… Basically, I have a working (more complex) version of this application, which is a project cost calculator. But because I am at the same time trying to learn to design my applications better, I would like some input on how I could improve this design. Basically the main thing I want is input on the conditionals that (here) appear repeated in two places. The suggestions I got before was to use the strategy pattern or factory pattern. I also know about the Martin Fowler book with the suggestion to Refactor conditional with polymorphism. I understand that principle in his simpler example. But how can I do either of these things here (if any would be suitable)? The way I see it, the calculation is dependent on a couple of conditions: 1. What kind of service is it, writing or analysis? 2. Is the project small, medium or large? (Please note that there may be other parameters as well, equally different, such as “are the products new or previously existing?” So such parameters should be possible to add, but I tried to keep the example simple with only two parameters to be able to get concrete help) So refactoring with polymorphism would imply creating a number of subclasses, which I already have for the first condition (type of service), and should I really create more subclasses for the second condition as well (size)? What would that become, AnalysisSmall, AnalysisMedium, AnalysisLarge, WritingSmall, etc…??? No, I know that’s not good, I just don’t see how to work with that pattern anyway else? I see the same problem basically for the suggestions of using the strategy pattern (and the factory pattern as I see it would just be a helper to achieve the polymorphism above). So please, if anyone has concrete suggestions as to how to design these classes the best way I would be really grateful! Please also consider whether I have chosen the objects correctly too, or if they need to be redesigned. (Responses like "you should consider the factory pattern" will obviously not be helpful... I've already been down that road and I'm stumped at precisely how in this case) Regards, Anders The code (very simplified, don’t mind the fact that I’m using strings instead of enums, not using a config file for data etc, that will be done as necessary in the real application once I get the hang of these design problems): public abstract class Service { protected Dictionary<string, int> _hours; protected const int SMALL = 2; protected const int MEDIUM = 8; public int NumberOfProducts { get; set; } public abstract int GetHours(); } public class Writing : Service { public Writing(int numberOfProducts) { NumberOfProducts = numberOfProducts; _hours = new Dictionary<string, int> { { "small", 125 }, { "medium", 100 }, { "large", 60 } }; } public override int GetHours() { if (NumberOfProducts <= SMALL) return _hours["small"] * NumberOfProducts; if (NumberOfProducts <= MEDIUM) return (_hours["small"] * SMALL) + (_hours["medium"] * (NumberOfProducts - SMALL)); return (_hours["small"] * SMALL) + (_hours["medium"] * (MEDIUM - SMALL)) + (_hours["large"] * (NumberOfProducts - MEDIUM)); } } public class Analysis : Service { public Analysis(int numberOfProducts) { NumberOfProducts = numberOfProducts; _hours = new Dictionary<string, int> { { "small", 56 }, { "medium", 104 }, { "large", 200 } }; } public override int GetHours() { if (NumberOfProducts <= SMALL) return _hours["small"]; if (NumberOfProducts <= MEDIUM) return _hours["medium"]; return _hours["large"]; } } public partial class Form1 : Form { public Form1() { InitializeComponent(); List<int> quantities = new List<int>(); for (int i = 0; i < 100; i++) { quantities.Add(i); } comboBoxNumberOfProducts.DataSource = quantities; } private void comboBoxNumberOfProducts_SelectedIndexChanged(object sender, EventArgs e) { Service writing = new Writing((int) comboBoxNumberOfProducts.SelectedItem); Service analysis = new Analysis((int) comboBoxNumberOfProducts.SelectedItem); labelWriterHours.Text = writing.GetHours().ToString(); labelAnalysisHours.Text = analysis.GetHours().ToString(); } }

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• A talk about observer pattern

  - by Martin

  As part of a university course I'm taking, I have to hold a 10 minute talk about the observer pattern. So far these are my points: What is it? (defenition) Polling is an alternative Polling VS Observer When Observer is better When Polling is better (taken from here) A statement that Mediator pattern is worth checking out. (I won't have time to cover it in 10 minutes) I would be happy to hear about: Any suggestions to add something? Another alternative (if exists)

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• wcf web service in post method, object properties are null, although the object is not null

  - by Abdalhadi Kolayb

  i have this problem in post method when i send object parameter to the method, then the object is not null, but all its properties have the default values. here is data module: [DataContract] public class Products { [DataMember(Order = 1)] public int ProdID { get; set; } [DataMember(Order = 2)] public string ProdName { get; set; } [DataMember(Order = 3)] public float PrpdPrice { get; set; } } and here is the interface: [OperationContract] [WebInvoke( Method = "POST", UriTemplate = "AddProduct", ResponseFormat = WebMessageFormat.Json, BodyStyle = WebMessageBodyStyle.WrappedRequest, RequestFormat = WebMessageFormat.Json)] string AddProduct([MessageParameter(Name = "prod")]Products prod); public string AddProduct(Products prod) { ProductsList.Add(prod); return "return string"; } here is the json request: Content-type:application/json {"prod":[{"ProdID": 111,"ProdName": "P111","PrpdPrice": 111}]} but in the server the object received: {"prod":[{"ProdID": 0,"ProdName": NULL,"PrpdPrice": 0}]}

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• Can a loosely typed language be considered true object oriented?

  - by user61852

  Can a loosely typed programming language like PHP be really considered object oriented? I mean, the methods don't have returning types and method parameters has no declared type either. Doesn't class design require methods to have a return type? Don't methods signatures have specifically-typed parameters? How can OOP techniques help you code in PHP if you always have to check the types of parameters received because the language doesn't enforce types? Please, if I'm wrong, explain it to me. When you design things using UML, then code classes in PHP with no return-typed methods and no-type parameters... Is the code really compliant with the UML design? You spend time designing the architecture of your software, then the compiler doesn't force the programmer to follow your design while coding, letting he/she assign any object variable to any other variable with no "type-mismatch" warning.

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• A couple of pattern matching issues with pattern matching in Lua

  - by Josh

  I'm fairly new to lua programming, but I'm also a quick study. I've been working on a weather forecaster for a program that I use, and it's working well, for the most part. Here is what I have so far. (Pay no attention to the zs.stuff. That is program specific and has no bearing on the lua coding.) if not http then http = require("socket.http") end local locale = string.gsub(zs.params(1),"%s+","%%20") local page = http.request("http://www.wunderground.com/cgi-bin/findweather/getForecast?query=" .. locale .. "&wuSelect=WEATHER") local location = string.match(page,'title="([%w%s,]+) RSS"') --print("Gathering weather information for " .. location .. ".") --local windspeed = string.match(page,'<span class="nobr"><span class="b">([%d.]+)</span>&nbsp;mph</span>') --print(windspeed) local condition = string.match(page, '<td class="vaM taC"><img src="http://icons-ecast.wxug.com/i/c/a/[%w_]+.gif" width="42" height="42" alt="[%w%s]+" class="condIcon" />') --local image = string.match(page, '<img src="http://icons-ecast.wxug.com/i/c/a/(.+).gif" width="42" height="42" alt="[%w%s]+" class="condIcon" />') local temperature = string.match(page,'pwsvariable="tempf" english="&deg;F" metric="&deg;C" value="([%d.]+)">') local humidity = string.match(page,'pwsvariable="humidity" english="" metric="" value="(%d+)"') zs.say(location) --zs.say("image ./Images/" .. image .. ".gif") zs.say("<color limegreen>Condition:</color> <color white>" .. condition .. "</color>") zs.say("<color limegreen>Temperature: </color><color white>" .. temperature .. "F</color>") zs.say("<color limegreen>Humidity: </color><color white>" .. humidity .. "%</color>") My main issue is this: I changed the 'condition' and added the 'image' variables to what they are now. Even though the line it's supposed to be matching comes directly from the webpage, it fails to match at all. So I'm wondering what it is I'm missing that's preventing this code from working. If I take out the <td class="vaM taC">< img src="http://icons-ecast.wxug.com/i/c/a/[%w_]+.gif" it'll match condition flawlessly. (For whatever reason, I can't get the above line to display correctly, but there is no space between the `< and img) Can anyone point out what is wrong with it? Aside from the pattern matching, I assure you the line is verbatim from the webpage. Another question I had is the ability to match across line breaks. Is there any possible way to do this? The reason why I ask is because on that same page, a few of the things I need to match are broken up on separate lines, and since the actual pattern I'm wanting to match shows up in other places on the page, I need to be able to match across line breaks to get the exact pattern. I appreciate any help in this matter!

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• NHibernate IUserType convert nullable DateTime to DB not-null value

  - by barakbbn

  I have legacy DB that store dates that means no-date as 9999-21-31, The column Till_Date is of type DateTime not-null="true". in the application i want to build persisted class that represent no-date as null, So i used nullable DateTime in C# //public DateTime? TillDate {get; set; } I created IUserType that knows to convert the entity null value to DB 9999-12-31 but it seems that NHibernate doesn't call SafeNullGet, SafeNullSet on my IUserType when the entity value is null, and report a null is used for not-null column. I tried to by-pass it by mapping the column as not-null="false" (changed only the mapping file, not the DB) but it still didn't help, only now it tries to insert the null value to the DB and get ADOException. Any knowledge if NHibernate doesn't support IUseType that convert null to not-null values? Thanks //Implementation public class NullableDateTimeToNotNullUserType : IUserType { private static readonly DateTime MaxDate = new DateTime(9999, 12, 31); public new bool Equals(object x, object y) { //This didn't work as well if (ReferenceEquals(x, y)) return true; //if(x == null && y == null) return false; if (x == null || y == null) return false; return x.Equals(y); } public int GetHashCode(object x) { return x == null ? 0 : x.GetHashCode(); } public object NullSafeGet(IDataReader rs, string[] names, object owner) { var value = rs.GetDateTime(rs.GetOrdinal(names[0])); return (value == MaxDate)? null : value; } public void NullSafeSet(IDbCommand cmd, object value, int index) { var dateValue = (DateTime?)value; var dbValue = (dateValue.HasValue) ? dateValue.Value : MaxDate; ((IDataParameter)cmd.Parameters[index]).Value = dbValue; } public object DeepCopy(object value) { return value; } public object Replace(object original, object target, object owner) { return original; } public object Assemble(object cached, object owner) { return cached; } public object Disassemble(object value) { return value; } public SqlType[] SqlTypes { get { return new[] { NHibernateUtil.DateTime.SqlType }; } } public Type ReturnedType { get { return typeof(DateTime?); } } public bool IsMutable { get { return false; } } } } //Final Implementation with fixes. make the column mapping in hbm.xml not-null="false" public class NullableDateTimeToNotNullUserType : IUserType { private static readonly DateTime MaxDate = new DateTime(9999, 12, 31); public new bool Equals(object x, object y) { //This didn't work as well if (ReferenceEquals(x, y)) return true; //if(x == null && y == null) return false; if (x == null || y == null) return false; return x.Equals(y); } public int GetHashCode(object x) { return x == null ? 0 : x.GetHashCode(); } public object NullSafeGet(IDataReader rs, string[] names, object owner) { var value = NHibernateUtil.Date.NullSafeGet(rs, names[0]); return (value == MaxDate)? default(DateTime?) : value; } public void NullSafeSet(IDbCommand cmd, object value, int index) { var dateValue = (DateTime?)value; var dbValue = (dateValue.HasValue) ? dateValue.Value : MaxDate; NHibernateUtil.Date.NullSafeSet(cmd, valueToSet, index); } public object DeepCopy(object value) { return value; } public object Replace(object original, object target, object owner) { return original; } public object Assemble(object cached, object owner) { return cached; } public object Disassemble(object value) { return value; } public SqlType[] SqlTypes { get { return new[] { NHibernateUtil.DateTime.SqlType }; } } public Type ReturnedType { get { return typeof(DateTime?); } } public bool IsMutable { get { return false; } } } }

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• The Endeca UI Design Pattern Library Returns

  - by Joe Lamantia

  I'm happy to announce that the Endeca UI Design Pattern Library - now titled the Endeca Discovery Pattern Library - is once again providing guidance and good practices on the design of discovery experiences.  Launched publicly in 2010 following several years of internal development and usage, the Endeca Pattern Library is a unique and valued source of industry-leading perspective on discovery - something I've come to appreciate directly through  fielding the consistent stream of inquiries about the library's status, and requests for its rapid return to public availability. Restoring the library as a public resource is only the first step!  For the next stage of the library's evolution, we plan to increase the scope of the guidance it offers beyond user interface design to the broader topic of discovery.  This could include patterns for architecture at the systems, user experience, and business levels; information and process models; analytical method and activity patterns for conducting discovery; and organizational and resource patterns for provisioning discovery capability in different settings.  We'd like guidance from the community on the kinds of patterns that are most valuable - so make sure to let us know. And we're also considering ways to increase the number of patterns the library offers, possibly by expanding the set of contributors and the authoring mechanisms. If you'd like to contribute, please get in touch. Here's the new address of the library: http://www.oracle.com/goto/EndecaDiscoveryPatterns And I should say 'Many thanks' to the UXDirect team and all the others within the Oracle family who helped - literally - keep the library alive, and restore it as a public resource.

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• Fetching Strategy example in repository pattern with pure POCO Entity framework

  - by Shawn Mclean

  I'm trying to roll out a strategy pattern with entity framework and the repository pattern using a simple example such as User and Post in which a user has many posts. From this answer here, I have the following domain: public interface IUser { public Guid UserId { get; set; } public string UserName { get; set; } public IEnumerable<Post> Posts { get; set; } } Add interfaces to support the roles in which you will use the user. public interface IAddPostsToUser : IUser { public void AddPost(Post post); } Now my repository looks like this: public interface IUserRepository { User Get<TRole>(Guid userId) where TRole : IUser; } Strategy (Where I'm stuck). What do I do with this code? Can I have an example of how to implement this, where do I put this? public interface IFetchingStrategy<TRole> { TRole Fetch(Guid id, IRepository<TRole> role) } My basic problem was what was asked in this question. I'd like to be able to get Users without posts and users with posts using the strategy pattern.

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• Using visitor pattern with large object hierarchy

  - by T. Fabre

  Context I've been using with a hierarchy of objects (an expression tree) a "pseudo" visitor pattern (pseudo, as in it does not use double dispatch) : public interface MyInterface { void Accept(SomeClass operationClass); } public class MyImpl : MyInterface { public void Accept(SomeClass operationClass) { operationClass.DoSomething(); operationClass.DoSomethingElse(); // ... and so on ... } } This design was, however questionnable, pretty comfortable since the number of implementations of MyInterface is significant (~50 or more) and I didn't need to add extra operations. Each implementation is unique (it's a different expression or operator), and some are composites (ie, operator nodes that will contain other operator/leaf nodes). Traversal is currently performed by calling the Accept operation on the root node of the tree, which in turns calls Accept on each of its child nodes, which in turn... and so on... But the time has come where I need to add a new operation, such as pretty printing : public class MyImpl : MyInterface { // Property does not come from MyInterface public string SomeProperty { get; set; } public void Accept(SomeClass operationClass) { operationClass.DoSomething(); operationClass.DoSomethingElse(); // ... and so on ... } public void Accept(SomePrettyPrinter printer) { printer.PrettyPrint(this.SomeProperty); } } I basically see two options : Keep the same design, adding a new method for my operation to each derived class, at the expense of maintainibility (not an option, IMHO) Use the "true" Visitor pattern, at the expense of extensibility (not an option, as I expect to have more implementations coming along the way...), with about 50+ overloads of the Visit method, each one matching a specific implementation ? Question Would you recommand using the Visitor pattern ? Is there any other pattern that could help solve this issue ?

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