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• Writing algorithm on 2D data set in plain english

  - by Alexandre P. Levasseur

  I have started an introductory Java class and the material is absolutely horrendous and I have to get excellent grades to be accepted into the master's degree, hence my very beginner question: In my assignment I have to write algorithms (no pseudo-code yet) to solve a board game (Sudoku). Essentially, the notes say that an algorithm is specification of the input(s), the output(s) and the treatments applied to the input to get the output. My question lies on the wording of algorithms because I could probably code it but I can't seem to put it on paper in a coherent way. The game has a 9x9 board and one of the algorithms to write has to find the solution by looking at 3 squares (either horizontal or vertical) and see if one of the three sub-squares match the number you are looking for. If none match then the number you are looking to place is in one of the other 2 set of 3 sub-squares (see image to get a better idea). I really can't get my head around how to formulate the solution into the terms described above or maybe it's just too simple, here's what I was thinking: Input: A 2-dimensional set of data of size 9 by 9 to be solved and a number to search for. Ouput: A 2-dimensional set of data of size 9 by 9 either solved or partially solved. Treatment: Scan each set of 3x9 and 9x3 squares. For each line or column of a 3x3 square check if the number matches a line (or column). If it does then move to the next line (or column). If not then proceed to the next 3x3 square in the same line (or column). Rinse and repeat. Does that make sense as an algorithm written in plain english ? I'm not looking for an answer to the algorithm per se but rather on the formulation of algorithms in plain english.

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• gl_PointCoord always zero

  - by Jonathan

  I am trying to draw point sprites in OpenGL with a shader but gl_PointCoord is always zero. Here is my code Setup: //Shader creation..(includes glBindAttribLocation(program, ATTRIB_P, "p");) glEnableVertexAttribArray(ATTRIB_P); In the rendering loop: glUseProgram(shader_particles); float vertices[]={0.0f,0.0f,0.0f}; glEnable(GL_TEXTURE_2D); glEnable(GL_POINT_SPRITE); glEnable(GL_VERTEX_PROGRAM_POINT_SIZE); //glTexEnvi(GL_POINT_SPRITE, GL_COORD_REPLACE, GL_TRUE);(tried with this on/off, doesn't work) glVertexAttribPointer(ATTRIB_P, 3, GL_FLOAT, GL_FALSE, 0, vertices); glDrawArrays(GL_POINTS, 0, 1); Vertex Shader: attribute highp vec4 p; void main() { gl_PointSize = 40.0f; gl_Position = p; } Fragment Shader: void main() { gl_FragColor = vec4(gl_PointCoord.st, 0, 1);//if the coords range from 0-1, this should draw a square with black,red,green,yellow corners } But this only draws a black square with a size of 40. What am I doing wrong? Edit: Point sprites work when i use the fixed function, but I need to use shaders because in the end the code will be for opengl es 2.0 glUseProgram(0); glEnable(GL_TEXTURE_2D); glEnable(GL_POINT_SPRITE); glTexEnvi(GL_POINT_SPRITE, GL_COORD_REPLACE, GL_TRUE); glPointSize(40); glBegin(GL_POINTS); glVertex3f(0.0f,0.0f,0.0f); glEnd(); Is anyone able to get point sprites working with shader? If so, please share some code.

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• Adding an Admin user to an ASP.NET MVC 4 application using a single drop-in file

  - by Jon Galloway

  I'm working on an ASP.NET MVC 4 tutorial and wanted to set it up so just dropping a file in App_Start would create a user named "Owner" and assign them to the "Administrator" role (more explanation at the end if you're interested). There are reasons why this wouldn't fit into most application scenarios: It's not efficient, as it checks for (and creates, if necessary) the user every time the app starts up The username, password, and role name are hardcoded in the app (although they could be pulled from config) Automatically creating an administrative account in code (without user interaction) could lead to obvious security issues if the user isn't informed However, with some modifications it might be more broadly useful - e.g. creating a test user with limited privileges, ensuring a required account isn't accidentally deleted, or - as in my case - setting up an account for demonstration or tutorial purposes. Challenge #1: Running on startup without requiring the user to install or configure anything I wanted to see if this could be done just by having the user drop a file into the App_Start folder and go. No copying code into Global.asax.cs, no installing addition NuGet packages, etc. That may not be the best approach - perhaps a NuGet package with a dependency on WebActivator would be better - but I wanted to see if this was possible and see if it offered the best experience. Fortunately ASP.NET 4 and later provide a PreApplicationStartMethod attribute which allows you to register a method which will run when the application starts up. You drop this attribute in your application and give it two parameters: a method name and the type that contains it. I created a static class named PreApplicationTasks with a static method named, then dropped this attribute in it: [assembly: PreApplicationStartMethod(typeof(PreApplicationTasks), "Initializer")] That's it. One small gotcha: the namespace can be a problem with assembly attributes. I decided my class didn't need a namespace. Challenge #2: Only one PreApplicationStartMethod per assembly In .NET 4, the PreApplicationStartMethod is marked as AllMultiple=false, so you can only have one PreApplicationStartMethod per assembly. This was fixed in .NET 4.5, as noted by Jon Skeet, so you can have as many PreApplicationStartMethods as you want (allowing you to keep your users waiting for the application to start indefinitely!). The WebActivator NuGet package solves the multiple instance problem if you're in .NET 4 - it registers as a PreApplicationStartMethod, then calls any methods you've indicated using [assembly: WebActivator.PreApplicationStartMethod(type, method)]. David Ebbo blogged about that here:  Light up your NuGets with startup code and WebActivator. In my scenario (bootstrapping a beginner level tutorial) I decided not to worry about this and stick with PreApplicationStartMethod. Challenge #3: PreApplicationStartMethod kicks in before configuration has been read This is by design, as Phil explains. It allows you to make changes that need to happen very early in the pipeline, well before Application_Start. That's fine in some cases, but it caused me problems when trying to add users, since the Membership Provider configuration hadn't yet been read - I got an exception stating that "Default Membership Provider could not be found." The solution here is to run code that requires configuration in a PostApplicationStart method. But how to do that? Challenge #4: Getting PostApplicationStartMethod without requiring WebActivator The WebActivator NuGet package, among other things, provides a PostApplicationStartMethod attribute. That's generally how I'd recommend running code that needs to happen after Application_Start: [assembly: WebActivator.PostApplicationStartMethod(typeof(TestLibrary.MyStartupCode), "CallMeAfterAppStart")] This works well, but I wanted to see if this would be possible without WebActivator. Hmm. Well, wait a minute - WebActivator works in .NET 4, so clearly it's registering and calling PostApplicationStartup tasks somehow. Off to the source code! Sure enough, there's even a handy comment in ActivationManager.cs which shows where PostApplicationStartup tasks are being registered: public static void Run() { if (!_hasInited) { RunPreStartMethods(); // Register our module to handle any Post Start methods. But outside of ASP.NET, just run them now if (HostingEnvironment.IsHosted) { Microsoft.Web.Infrastructure.DynamicModuleHelper.DynamicModuleUtility.RegisterModule(typeof(StartMethodCallingModule)); } else { RunPostStartMethods(); } _hasInited = true; } } Excellent. Hey, that DynamicModuleUtility seems familiar... Sure enough, K. Scott Allen mentioned it on his blog last year. This is really slick - a PreApplicationStartMethod can register a new HttpModule in code. Modules are run right after application startup, so that's a perfect time to do any startup stuff that requires configuration to be read. As K. Scott says, it's this easy: using System; using System.Web; using Microsoft.Web.Infrastructure.DynamicModuleHelper; [assembly:PreApplicationStartMethod(typeof(MyAppStart), "Start")] public class CoolModule : IHttpModule { // implementation not important // imagine something cool here } public static class MyAppStart { public static void Start() { DynamicModuleUtility.RegisterModule(typeof(CoolModule)); } } Challenge #5: Cooperating with SimpleMembership The ASP.NET MVC Internet template includes SimpleMembership. SimpleMembership is a big improvement over traditional ASP.NET Membership. For one thing, rather than forcing a database schema, it can work with your database schema. In the MVC 4 Internet template case, it uses Entity Framework Code First to define the user model. SimpleMembership bootstrap includes a call to InitializeDatabaseConnection, and I want to play nice with that. There's a new [InitializeSimpleMembership] attribute on the AccountController, which calls \Filters\InitializeSimpleMembershipAttribute.cs::OnActionExecuting(). That comment in that method that says "Ensure ASP.NET Simple Membership is initialized only once per app start" which sounds like good advice. I figured the best thing would be to call that directly: new Mvc4SampleApplication.Filters.InitializeSimpleMembershipAttribute().OnActionExecuting(null); I'm not 100% happy with this - in fact, it's my least favorite part of this solution. There are two problems - first, directly calling a method on a filter, while legal, seems odd. Worse, though, the Filter lives in the application's namespace, which means that this code no longer works well as a generic drop-in. The simplest workaround would be to duplicate the relevant SimpleMembership initialization code into my startup code, but I'd rather not. I'm interested in your suggestions here. Challenge #6: Module Init methods are called more than once When debugging, I noticed (and remembered) that the Init method may be called more than once per page request - it's run once per instance in the app pool, and an individual page request can cause multiple resource requests to the server. While SimpleMembership does have internal checks to prevent duplicate user or role entries, I'd rather not cause or handle those exceptions. So here's the standard single-use lock in the Module's init method: void IHttpModule.Init(HttpApplication context) { lock (lockObject) { if (!initialized) { //Do stuff } initialized = true; } } Putting it all together With all of that out of the way, here's the code I came up with: using Mvc4SampleApplication.Filters; using System.Web; using System.Web.Security; using WebMatrix.WebData; [assembly: PreApplicationStartMethod(typeof(PreApplicationTasks), "Initializer")] public static class PreApplicationTasks { public static void Initializer() { Microsoft.Web.Infrastructure.DynamicModuleHelper.DynamicModuleUtility .RegisterModule(typeof(UserInitializationModule)); } } public class UserInitializationModule : IHttpModule { private static bool initialized; private static object lockObject = new object(); private const string _username = "Owner"; private const string _password = "p@ssword123"; private const string _role = "Administrator"; void IHttpModule.Init(HttpApplication context) { lock (lockObject) { if (!initialized) { new InitializeSimpleMembershipAttribute().OnActionExecuting(null); if (!WebSecurity.UserExists(_username)) WebSecurity.CreateUserAndAccount(_username, _password); if (!Roles.RoleExists(_role)) Roles.CreateRole(_role); if (!Roles.IsUserInRole(_username, _role)) Roles.AddUserToRole(_username, _role); } initialized = true; } } void IHttpModule.Dispose() { } } The Verdict: Is this a good thing? Maybe. I think you'll agree that the journey was undoubtedly worthwhile, as it took us through some of the finer points of hooking into application startup, integrating with membership, and understanding why the WebActivator NuGet package is so useful Will I use this in the tutorial? I'm leaning towards no - I think a NuGet package with a dependency on WebActivator might work better: It's a little more clear what's going on Installing a NuGet package might be a little less error prone than copying a file A novice user could uninstall the package when complete It's a good introduction to NuGet, which is a good thing for beginners to see This code either requires either duplicating a little code from that filter or modifying the file to use the namespace Honestly I'm undecided at this point, but I'm glad that I can weigh the options. If you're interested: Why are you doing this? I'm updating the MVC Music Store tutorial to ASP.NET MVC 4, taking advantage of a lot of new ASP.NET MVC 4 features and trying to simplify areas that are giving people trouble. One change that addresses both needs us using the new OAuth support for membership as much as possible - it's a great new feature from an application perspective, and we get a fair amount of beginners struggling with setting up membership on a variety of database and development setups, which is a distraction from the focus of the tutorial - learning ASP.NET MVC. Side note: Thanks to some great help from Rick Anderson, we had a draft of the tutorial that was looking pretty good earlier this summer, but there were enough changes in ASP.NET MVC 4 all the way up to RTM that there's still some work to be done. It's high priority and should be out very soon. The one issue I ran into with OAuth is that we still need an Administrative user who can edit the store's inventory. I thought about a number of solutions for that - making the first user to register the admin, or the first user to use the username "Administrator" is assigned to the Administrator role - but they both ended up requiring extra code; also, I worried that people would use that code without understanding it or thinking about whether it was a good fit.

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• C#/.NET Little Wonders: Fun With Enum Methods

  - by James Michael Hare

  Once again lets dive into the Little Wonders of .NET, those small things in the .NET languages and BCL classes that make development easier by increasing readability, maintainability, and/or performance. So probably every one of us has used an enumerated type at one time or another in a C# program.  The enumerated types we create are a great way to represent that a value can be one of a set of discrete values (or a combination of those values in the case of bit flags). But the power of enum types go far beyond simple assignment and comparison, there are many methods in the Enum class (that all enum types “inherit” from) that can give you even more power when dealing with them. IsDefined() – check if a given value exists in the enum Are you reading a value for an enum from a data source, but are unsure if it is actually a valid value or not?  Casting won’t tell you this, and Parse() isn’t guaranteed to balk either if you give it an int or a combination of flags.  So what can we do? Let’s assume we have a small enum like this for result codes we want to return back from our business logic layer: 1: public enum ResultCode 2: { 3: Success, 4: Warning, 5: Error 6: } In this enum, Success will be zero (unless given another value explicitly), Warning will be one, and Error will be two. So what happens if we have code like this where perhaps we’re getting the result code from another data source (could be database, could be web service, etc)? 1: public ResultCode PerformAction() 2: { 3: // set up and call some method that returns an int. 4: int result = ResultCodeFromDataSource(); 5:  6: // this will suceed even if result is < 0 or > 2. 7: return (ResultCode) result; 8: } So what happens if result is –1 or 4?  Well, the cast does not fail, so what we end up with would be an instance of a ResultCode that would have a value that’s outside of the bounds of the enum constants we defined. This means if you had a block of code like: 1: switch (result) 2: { 3: case ResultType.Success: 4: // do success stuff 5: break; 6:  7: case ResultType.Warning: 8: // do warning stuff 9: break; 10:  11: case ResultType.Error: 12: // do error stuff 13: break; 14: } That you would hit none of these blocks (which is a good argument for always having a default in a switch by the way). So what can you do?  Well, there is a handy static method called IsDefined() on the Enum class which will tell you if an enum value is defined.  1: public ResultCode PerformAction() 2: { 3: int result = ResultCodeFromDataSource(); 4:  5: if (!Enum.IsDefined(typeof(ResultCode), result)) 6: { 7: throw new InvalidOperationException("Enum out of range."); 8: } 9:  10: return (ResultCode) result; 11: } In fact, this is often recommended after you Parse() or cast a value to an enum as there are ways for values to get past these methods that may not be defined. If you don’t like the syntax of passing in the type of the enum, you could clean it up a bit by creating an extension method instead that would allow you to call IsDefined() off any isntance of the enum: 1: public static class EnumExtensions 2: { 3: // helper method that tells you if an enum value is defined for it's enumeration 4: public static bool IsDefined(this Enum value) 5: { 6: return Enum.IsDefined(value.GetType(), value); 7: } 8: }   HasFlag() – an easier way to see if a bit (or bits) are set Most of us who came from the land of C programming have had to deal extensively with bit flags many times in our lives.  As such, using bit flags may be almost second nature (for a quick refresher on bit flags in enum types see one of my old posts here). However, in higher-level languages like C#, the need to manipulate individual bit flags is somewhat diminished, and the code to check for bit flag enum values may be obvious to an advanced developer but cryptic to a novice developer. For example, let’s say you have an enum for a messaging platform that contains bit flags: 1: // usually, we pluralize flags enum type names 2: [Flags] 3: public enum MessagingOptions 4: { 5: None = 0, 6: Buffered = 0x01, 7: Persistent = 0x02, 8: Durable = 0x04, 9: Broadcast = 0x08 10: } We can combine these bit flags using the bitwise OR operator (the ‘|’ pipe character): 1: // combine bit flags using 2: var myMessenger = new Messenger(MessagingOptions.Buffered | MessagingOptions.Broadcast); Now, if we wanted to check the flags, we’d have to test then using the bit-wise AND operator (the ‘&’ character): 1: if ((options & MessagingOptions.Buffered) == MessagingOptions.Buffered) 2: { 3: // do code to set up buffering... 4: // ... 5: } While the ‘|’ for combining flags is easy enough to read for advanced developers, the ‘&’ test tends to be easy for novice developers to get wrong.  First of all you have to AND the flag combination with the value, and then typically you should test against the flag combination itself (and not just for a non-zero)!  This is because the flag combination you are testing with may combine multiple bits, in which case if only one bit is set, the result will be non-zero but not necessarily all desired bits! Thanks goodness in .NET 4.0 they gave us the HasFlag() method.  This method can be called from an enum instance to test to see if a flag is set, and best of all you can avoid writing the bit wise logic yourself.  Not to mention it will be more readable to a novice developer as well: 1: if (options.HasFlag(MessagingOptions.Buffered)) 2: { 3: // do code to set up buffering... 4: // ... 5: } It is much more concise and unambiguous, thus increasing your maintainability and readability. It would be nice to have a corresponding SetFlag() method, but unfortunately generic types don’t allow you to specialize on Enum, which makes it a bit more difficult.  It can be done but you have to do some conversions to numeric and then back to the enum which makes it less of a payoff than having the HasFlag() method.  But if you want to create it for symmetry, it would look something like this: 1: public static T SetFlag<T>(this Enum value, T flags) 2: { 3: if (!value.GetType().IsEquivalentTo(typeof(T))) 4: { 5: throw new ArgumentException("Enum value and flags types don't match."); 6: } 7:  8: // yes this is ugly, but unfortunately we need to use an intermediate boxing cast 9: return (T)Enum.ToObject(typeof (T), Convert.ToUInt64(value) | Convert.ToUInt64(flags)); 10: } Note that since the enum types are value types, we need to assign the result to something (much like string.Trim()).  Also, you could chain several SetFlag() operations together or create one that takes a variable arg list if desired. Parse() and ToString() – transitioning from string to enum and back Sometimes, you may want to be able to parse an enum from a string or convert it to a string - Enum has methods built in to let you do this.  Now, many may already know this, but may not appreciate how much power are in these two methods. For example, if you want to parse a string as an enum, it’s easy and works just like you’d expect from the numeric types: 1: string optionsString = "Persistent"; 2:  3: // can use Enum.Parse, which throws if finds something it doesn't like... 4: var result = (MessagingOptions)Enum.Parse(typeof (MessagingOptions), optionsString); 5:  6: if (result == MessagingOptions.Persistent) 7: { 8: Console.WriteLine("It worked!"); 9: } Note that Enum.Parse() will throw if it finds a value it doesn’t like.  But the values it likes are fairly flexible!  You can pass in a single value, or a comma separated list of values for flags and it will parse them all and set all bits: 1: // for string values, can have one, or comma separated. 2: string optionsString = "Persistent, Buffered"; 3:  4: var result = (MessagingOptions)Enum.Parse(typeof (MessagingOptions), optionsString); 5:  6: if (result.HasFlag(MessagingOptions.Persistent) && result.HasFlag(MessagingOptions.Buffered)) 7: { 8: Console.WriteLine("It worked!"); 9: } Or you can parse in a string containing a number that represents a single value or combination of values to set: 1: // 3 is the combination of Buffered (0x01) and Persistent (0x02) 2: var optionsString = "3"; 3:  4: var result = (MessagingOptions) Enum.Parse(typeof (MessagingOptions), optionsString); 5:  6: if (result.HasFlag(MessagingOptions.Persistent) && result.HasFlag(MessagingOptions.Buffered)) 7: { 8: Console.WriteLine("It worked again!"); 9: } And, if you really aren’t sure if the parse will work, and don’t want to handle an exception, you can use TryParse() instead: 1: string optionsString = "Persistent, Buffered"; 2: MessagingOptions result; 3:  4: // try parse returns true if successful, and takes an out parm for the result 5: if (Enum.TryParse(optionsString, out result)) 6: { 7: if (result.HasFlag(MessagingOptions.Persistent) && result.HasFlag(MessagingOptions.Buffered)) 8: { 9: Console.WriteLine("It worked!"); 10: } 11: } So we covered parsing a string to an enum, what about reversing that and converting an enum to a string?  The ToString() method is the obvious and most basic choice for most of us, but did you know you can pass a format string for enum types that dictate how they are written as a string?: 1: MessagingOptions value = MessagingOptions.Buffered | MessagingOptions.Persistent; 2:  3: // general format, which is the default, 4: Console.WriteLine("Default : " + value); 5: Console.WriteLine("G (default): " + value.ToString("G")); 6:  7: // Flags format, even if type does not have Flags attribute. 8: Console.WriteLine("F (flags) : " + value.ToString("F")); 9:  10: // integer format, value as number. 11: Console.WriteLine("D (num) : " + value.ToString("D")); 12:  13: // hex format, value as hex 14: Console.WriteLine("X (hex) : " + value.ToString("X")); Which displays: 1: Default : Buffered, Persistent 2: G (default): Buffered, Persistent 3: F (flags) : Buffered, Persistent 4: D (num) : 3 5: X (hex) : 00000003 Now, you may not really see a difference here between G and F because I used a [Flags] enum, the difference is that the “F” option treats the enum as if it were flags even if the [Flags] attribute is not present.  Let’s take a non-flags enum like the ResultCode used earlier: 1: // yes, we can do this even if it is not [Flags] enum. 2: ResultCode value = ResultCode.Warning | ResultCode.Error; And if we run that through the same formats again we get: 1: Default : 3 2: G (default): 3 3: F (flags) : Warning, Error 4: D (num) : 3 5: X (hex) : 00000003 Notice that since we had multiple values combined, but it was not a [Flags] marked enum, the G and default format gave us a number instead of a value name.  This is because the value was not a valid single-value constant of the enum.  However, using the F flags format string, it broke out the value into its component flags even though it wasn’t marked [Flags]. So, if you want to get an enum to display appropriately for whether or not it has the [Flags] attribute, use G which is the default.  If you always want it to attempt to break down the flags, use F.  For numeric output, obviously D or  X are the best choice depending on whether you want decimal or hex. Summary Hopefully, you learned a couple of new tricks with using the Enum class today!  I’ll add more little wonders as I think of them and thanks for all the invaluable input!   Technorati Tags: C#,.NET,Little Wonders,Enum,BlackRabbitCoder

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• Conflict between variable substitution and CJK characters in BASH

  - by AndreasT

  I encountered a problem with variable substitution in the BASH shell. Say you define a variable a. Then the command $> echo ${a//[0-4]/} prints its value with all the numbers ranged between 0 and 4 removed: $> a="Hello1265-3World" $> echo ${a//[0-4]/} Hello65-World This seems to work just fine, but let's take a look at the next example: $> b="?1265-3?" $> echo ${b//[0-4]/} ?1265-3? Substitution did not take place: I assume that is because b contains CJK characters. This issue extends to all cases in which square brackets are involved. Surprisingly enough, variable substitution without square brackets works fine in both cases: $> a="Hello1265-3World" $> echo ${a//2/} Hello165-3World $> b="?1265-3?" $> echo ${b//2/} ?165-3? Is it a bug or am I missing something? I use Lubuntu 12.04, terminal is lxterminal and echo $BASH_VERSION returns 4.2.24(1)-release. EDIT: Andrew Johnson in his comment stated that with gnome-terminal 4.2.37(1)-release the command works fine. I wonder whether it is a problem of lxterminal or of its specific 4.2.24(1)-release version.

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• Explain DNS/Content/Registration with services such as Blogger and Go Daddy

  - by user8926

  I have this kind of settings for Google Sites and Blogger in Godaddy, below. I cannot get URL Framing (not URL masking) working with them. I am unsure what the problem, cannot understand what services such as Blogger and Godaddy really do. Wrong A-records in Go Daddy! ; A Records @ 3600 IN A 216.239.32.21 art 3600 IN A 64.202.189.170 abc 3600 IN A 64.202.189.170 @ 3600 IN A 216.239.34.21 @ 3600 IN A 216.239.36.21 @ 3600 IN A 216.239.38.21 lol 3600 IN A 64.202.189.170 ; CNAME Records www 3600 IN CNAME ghs.google.com mobilemail 3600 IN CNAME mobilemail-v01.prod.mesa1.secureserver.net pda 3600 IN CNAME mobilemail-v01.prod.mesa1.secureserver.net email 3600 IN CNAME email.secureserver.net imap 3600 IN CNAME imap.secureserver.net mail 3600 IN CNAME pop.secureserver.net pop 3600 IN CNAME pop.secureserver.net smtp 3600 IN CNAME smtp.secureserver.net ftp 3600 IN CNAME @ webmail 3600 IN CNAME webmail.secureserver.net e 3600 IN CNAME email.secureserver.net Please, explain the "Custom Domain" and how can I hide my blogger url? ok I am still unsure what the "custom domain" in blogger really mean, does it mean that the content hosting is moved to some other site? Or does it mean that it just hides the blogspot url with other url? Or is it this so-called "301" thing or "URL redirection" or something else? Related questions Control Content Hosting, DNS Hosting and Registration with command line?

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• Code Reuse is (Damn) Hard

  - by James Michael Hare

  Being a development team lead, the task of interviewing new candidates was part of my job.  Like any typical interview, we started with some easy questions to get them warmed up and help calm their nerves before hitting the hard stuff. One of those easier questions was almost always: “Name some benefits of object-oriented development.”  Nearly every time, the candidate would chime in with a plethora of canned answers which typically included: “it helps ease code reuse.”  Of course, this is a gross oversimplification.  Tools only ease reuse, its developers that ultimately can cause code to be reusable or not, regardless of the language or methodology. But it did get me thinking…  we always used to say that as part of our mantra as to why Object-Oriented Programming was so great.  With polymorphism, inheritance, encapsulation, etc. we in essence set up the concepts to help facilitate reuse as much as possible.  And yes, as a developer now of many years, I unquestionably held that belief for ages before it really struck me how my views on reuse have jaded over the years.  In fact, in many ways Agile rightly eschews reuse as taking a backseat to developing what's needed for the here and now.  It used to be I was in complete opposition to that view, but more and more I've come to see the logic in it.  Too many times I've seen developers (myself included) get lost in design paralysis trying to come up with the perfect abstraction that would stand all time.  Nearly without fail, all of these pieces of code become obsolete in a matter of months or years. It’s not that I don’t like reuse – it’s just that reuse is hard.  In fact, reuse is DAMN hard.  Many times it is just a distraction that eats up architect and developer time, and worse yet can be counter-productive and force wrong decisions.  Now don’t get me wrong, I love the idea of reusable code when it makes sense.  These are in the few cases where you are designing something that is inherently reusable.  The problem is, most business-class code is inherently unfit for reuse! Furthermore, the code that is reusable will often fail to be reused if you don’t have the proper framework in place for effective reuse that includes standardized versioning, building, releasing, and documenting the components.  That should always be standard across the board when promoting reusable code.  All of this is hard, and it should only be done when you have code that is truly reusable or you will be exerting a large amount of development effort for very little bang for your buck. But my goal here is not to get into how to reuse (that is a topic unto itself) but what should be reused.  First, let’s look at an extension method.  There’s many times where I want to kick off a thread to handle a task, then when I want to reign that thread in of course I want to do a Join on it.  But what if I only want to wait a limited amount of time and then Abort?  Well, I could of course write that logic out by hand each time, but it seemed like a great extension method: 1: public static class ThreadExtensions 2: { 3: public static bool JoinOrAbort(this Thread thread, TimeSpan timeToWait) 4: { 5: bool isJoined = false; 6:  7: if (thread != null) 8: { 9: isJoined = thread.Join(timeToWait); 10:  11: if (!isJoined) 12: { 13: thread.Abort(); 14: } 15: } 16: return isJoined; 17: } 18: } 19:  When I look at this code, I can immediately see things that jump out at me as reasons why this code is very reusable.  Some of them are standard OO principles, and some are kind-of home grown litmus tests: Single Responsibility Principle (SRP) – The only reason this extension method need change is if the Thread class itself changes (one responsibility). Stable Dependencies Principle (SDP) – This method only depends on classes that are more stable than it is (System.Threading.Thread), and in itself is very stable, hence other classes may safely depend on it. It is also not dependent on any business domain, and thus isn't subject to changes as the business itself changes. Open-Closed Principle (OCP) – This class is inherently closed to change. Small and Stable Problem Domain – This method only cares about System.Threading.Thread. All-or-None Usage – A user of a reusable class should want the functionality of that class, not parts of that functionality.  That’s not to say they most use every method, but they shouldn’t be using a method just to get half of its result. Cost of Reuse vs. Cost to Recreate – since this class is highly stable and minimally complex, we can offer it up for reuse very cheaply by promoting it as “ready-to-go” and already unit tested (important!) and available through a standard release cycle (very important!). Okay, all seems good there, now lets look at an entity and DAO.  I don’t know about you all, but there have been times I’ve been in organizations that get the grand idea that all DAOs and entities should be standardized and shared.  While this may work for small or static organizations, it’s near ludicrous for anything large or volatile. 1: namespace Shared.Entities 2: { 3: public class Account 4: { 5: public int Id { get; set; } 6:  7: public string Name { get; set; } 8:  9: public Address HomeAddress { get; set; } 10:  11: public int Age { get; set;} 12:  13: public DateTime LastUsed { get; set; } 14:  15: // etc, etc, etc... 16: } 17: } 18:  19: ... 20:  21: namespace Shared.DataAccess 22: { 23: public class AccountDao 24: { 25: public Account FindAccount(int id) 26: { 27: // dao logic to query and return account 28: } 29:  30: ... 31:  32: } 33: } Now to be fair, I’m not saying there doesn’t exist an organization where some entites may be extremely static and unchanging.  But at best such entities and DAOs will be problematic cases of reuse.  Let’s examine those same tests: Single Responsibility Principle (SRP) – The reasons to change for these classes will be strongly dependent on what the definition of the account is which can change over time and may have multiple influences depending on the number of systems an account can cover. Stable Dependencies Principle (SDP) – This method depends on the data model beneath itself which also is largely dependent on the business definition of an account which can be very inherently unstable. Open-Closed Principle (OCP) – This class is not really closed for modification.  Every time the account definition may change, you’d need to modify this class. Small and Stable Problem Domain – The definition of an account is inherently unstable and in fact may be very large.  What if you are designing a system that aggregates account information from several sources? All-or-None Usage – What if your view of the account encompasses data from 3 different sources but you only care about one of those sources or one piece of data?  Should you have to take the hit of looking up all the other data?  On the other hand, should you have ten different methods returning portions of data in chunks people tend to ask for?  Neither is really a great solution. Cost of Reuse vs. Cost to Recreate – DAOs are really trivial to rewrite, and unless your definition of an account is EXTREMELY stable, the cost to promote, support, and release a reusable account entity and DAO are usually far higher than the cost to recreate as needed. It’s no accident that my case for reuse was a utility class and my case for non-reuse was an entity/DAO.  In general, the smaller and more stable an abstraction is, the higher its level of reuse.  When I became the lead of the Shared Components Committee at my workplace, one of the original goals we looked at satisfying was to find (or create), version, release, and promote a shared library of common utility classes, frameworks, and data access objects.  Now, of course, many of you will point to nHibernate and Entity for the latter, but we were looking at larger, macro collections of data that span multiple data sources of varying types (databases, web services, etc). As we got deeper and deeper in the details of how to manage and release these items, it quickly became apparent that while the case for reuse was typically a slam dunk for utilities and frameworks, the data access objects just didn’t “smell” right.  We ended up having session after session of design meetings to try and find the right way to share these data access components. When someone asked me why it was taking so long to iron out the shared entities, my response was quite simple, “Reuse is hard...”  And that’s when I realized, that while reuse is an awesome goal and we should strive to make code maintainable, often times you end up creating far more work for yourself than necessary by trying to force code to be reusable that inherently isn’t. Think about classes the times you’ve worked in a company where in the design session people fight over the best way to implement a class to make it maximally reusable, extensible, and any other buzzwordable.  Then think about how quickly that design became obsolete.  Many times I set out to do a project and think, “yes, this is the best design, I can extend it easily!” only to find out the business requirements change COMPLETELY in such a way that the design is rendered invalid.  Code, in general, tends to rust and age over time.  As such, writing reusable code can often be difficult and many times ends up being a futile exercise and worse yet, sometimes makes the code harder to maintain because it obfuscates the design in the name of extensibility or reusability. So what do I think are reusable components? Generic Utility classes – these tend to be small classes that assist in a task and have no business context whatsoever. Implementation Abstraction Frameworks – home-grown frameworks that try to isolate changes to third party products you may be depending on (like writing a messaging abstraction layer for publishing/subscribing that is independent of whether you use JMS, MSMQ, etc). Simplification and Uniformity Frameworks – To some extent this is similar to an abstraction framework, but there may be one chosen provider but a development shop mandate to perform certain complex items in a certain way.  Or, perhaps to simplify and dumb-down a complex task for the average developer (such as implementing a particular development-shop’s method of encryption). And what are less reusable? Application and Business Layers – tend to fluctuate a lot as requirements change and new features are added, so tend to be an unstable dependency.  May be reused across applications but also very volatile. Entities and Data Access Layers – these tend to be tuned to the scope of the application, so reusing them can be hard unless the abstract is very stable. So what’s the big lesson?  Reuse is hard.  In fact it’s damn hard.  And much of the time I’m not convinced we should focus too hard on it. If you’re designing a utility or framework, then by all means design it for reuse.  But you most also really set down a good versioning, release, and documentation process to maximize your chances.  For anything else, design it to be maintainable and extendable, but don’t waste the effort on reusability for something that most likely will be obsolete in a year or two anyway.

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• Warnings When Undo Isn't Possible

  - by ultan o'broin

  Enjoyed this post Never Use a Warning When you Mean Undo by Aza Raskin. It makes sense never to warn users if an undo option is possible. The examples given are from the web space. Here's the conclusion: Warnings cause us to lose our work, to mistrust our computers, and to blame ourselves. A simple but foolproof design methodology solves the problem: "Never use a warning when you mean undo." And when a user is deleting their work, you always mean undo. However, in enterprise apps you may find that an undo option isn't technically possible or desirable. Objects may be shared, part of a flow elsewhere, or undoing something committed to the database (a rollback I guess) may not be feasible if it becomes locked by another process. Plus, what constitutes user ownership of objects isn't always clear to users. The implications of delete (and other) actions need to be clearly communicated out in advance. Really, warnings are important in the enterprise space. Data has a very high value, and users can perform a wide variety of actions that may risk that data, not always within the application itself (at browser level, for example). That said, throwing warnings all over the place when an undo option is possible is annoying. Instead, treat warnings with respect. When there is no undo option possible, use warning messages to communicate potentially dangerous or irrecoverable actions or the downstream consequences of user actions on the process or task flow. Force the user to respond to a warning message by using a modal dialog with clearly labeled action buttons. Here's a couple of examples. A great article that got me thinking. Let's see more like that. Let's not forget there's more types of messages than just error messages. User assistance and user experience professionals need to understand when best to use confirmation, information, and warning types too!

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• Alt-Tab looses focus and have to hit Alt-Grave Accent to get focus

  - by John Hamill

  Alt-Tab looses focus and have to hit Alt-Grave Accent to get focus I have ubuntu 12.4 with Unity window manager. I have a gvim window and a firefox window open. I hit Alt-Tab to switch between the two. Sometimes the gvim window doesn't have focus and I have to hit Alt-GraveAccent (Alt-`) to get the gvim window to have focus (ie: have the cursor a solid white square instead of a outline of a square) I do this to move between firefox where I highlight some text and do a copy, then Alt-Tab to gvim and do a paste. Sometimes the focus isn't in gvim and the paste doesn't work. I then have to do an Alt-graveAccent to get the focus into gvim or click the gvim window. These extra steps slow my process down and it makes it difficult to get into a smooth rythum. I saw this: ALT+TAB loses focus Maybe the Alt-GraveAccent may help someone. It's a unity bug: https://bugs.launchpad.net/ubuntu/+source/unity/+bug/1035628 Your best bet is to wait until an update comes through fixing it.

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• How can I move a polygon edge 1 unit away from the center?

  - by Stephen

  Let's say I have a polygon class that is represented by a list of vector classes as vertices, like so: var Vector = function(x, y) { this.x = x; this.y = y; }, Polygon = function(vectors) { this.vertices = vectors; }; Now I make a polygon (in this case, a square) like so: var poly = new Polygon([ new Vector(2, 2), new Vector(5, 2), new Vector(5, 5), new Vector(2, 5) ]); So, the top edge would be [poly.vertices[0], poly.vertices[1]]. I need to stretch this polygon by moving each edge away from the center of the polygon by one unit, along that edge's normal. The following example shows the first edge, the top, moved one unit up: The final polygon should look like this new one: var finalPoly = new Polygon([ new Vector(1, 1), new Vector(6, 1), new Vector(6, 6), new Vector(1, 6) ]); It is important that I iterate, moving one edge at a time, because I will be doing some collision tests after moving each edge. Here is what I tried so far (simplified for clarity), which fails triumphantly: for(var i = 0; i < vertices.length; i++) { var a = vertices[i], b = vertices[i + 1] || vertices[0]; // in case of final vertex var ax = a.x, ay = a.y, bx = b.x, by = b.y; // get some new perpendicular vectors var a2 = new Vector(-ay, ax), b2 = new Vector(-by, bx); // make into unit vectors a2.convertToUnitVector(); b2.convertToUnitVector(); // add the new vectors to the original ones a.add(a2); b.add(b2); // the rest of the code, collision tests, etc. } This makes my polygon start slowly rotating and sliding to the left, instead of what I need. Finally, the example shows a square, but the polygons in question could be anything. They will always be convex, and always with vertices in clockwise order.

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• Performance issues with visibility detection and object transparency

  - by maul

  I'm working on a 3d game that has a view similar to classic isometric games (diablo, etc.). One of the things I'm trying to implement is the effect of turning walls transparent when the player walks behind them. By itself this is not a huge issue, but I'm having trouble determining which walls should be transparent exactly. I can't use a circle or square mask. There are a lot of cases where the wall piece at the same (relative) position has different visibility depending on the surrounding area. With the help of a friend I came up with this algorithm: Create a grid around the player that contains a lot of "visibility points" (my game is semi tile-based so I create one point for every tile on the grid) - the size of the square's side is close to the radius where I make objects transparent. I found 6x6 to be a good value, so that's 36 visibility points total. For every visibility point on the grid, check if that point is in the player's line of sight. For every visibility point that is in the LOS, cast a ray from the camera to that point and mark all objects the ray hits as transparent. This algorithm works - not perfectly, but only requires some tuning - however this is very slow. As you can see, it requries 36 ray casts minimum, but most of the time 60-70 depending on the position. That's simply too much for the CPU. Is there a better way to do this? I'm using Unity 3D but I'm not looking for an engine-specific solution.

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• NRF Big Show 2011 -- Part 1

  - by David Dorf

  When Apple decided to open retail stores, they came to 360Commerce (now part of Oracle Retail) to help with the secret project. Similarly, when Disney Stores decided to reinvent itself, they also came to us for their POS system. In both cases visiting a store is an experience where sales take a backseat to entertainment, exploration, and engagement This quote from a recent Stores Magazine article says it all: "We compete based on an experience, emotion and immersion like Disney," says Neal Lassila, vice president of global information technology for Disney. "That's opposed to [competing] on price and hawking a doll for $19.99. There is no sales pressure technique." Instead, it's about delivering "a great time." While you're attending the NRF conference in New York next week, you'll definitely want to stop by the new 20,000 square-foot Disney store in Times Square. If you're not attending, you can always check out the videos to get a feel for the stores' vibe. This year we've invited Disney Stores to open a pop-up store within the Oracle Retail booth. There will be lots of items on sale that fit in your suitcase, and there's no better way to demonstrate our POS, including the mobile POS running on an iPod Touch. You should also plan to attend Tuesday morning's super-session The Magic of the Disney Store: An Immersive Retail Experience with Steve Finney. In the case of Apple and Disney, less POS is actually a good thing. In both cases it was important to make the checkout process fast and easy so as not to detract from the overall experience. There will be ample opportunities to see this play out in New York next week, so I hope you take advantage.

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• Pythonic use of the isinstance function?

  - by Pace

  Whenever I find myself wanting to use the isinstance() function I usually know that I'm doing something wrong and end up changing my ways. However, in this case I think I have a valid use for it. I will use shapes to illustrate my point although I am not actually working with shapes. I am parsing XML configuration files that look like the following: <square> <width>7</width> </square> <rectangle> <width>5</width> <height>7</height> </rectangle> <circle> <radius>4</radius> </circle> For each element I create an instance of the Shape class and build up a list of Shape objects in a class called the ShapeContainer. Different parts of the rest of my application need to refer to the ShapeContainer to get certain shapes. Depending on what the code is doing it might need just rectangles, or it might operate on all quadrangles, or it might operate on all shapes. I have created the following function in the ShapeContainer class (the actual function uses a list comprehension but I have expanded it here for readability): def locate(self, shapeClass): result = [] for shape in self.__shapes: if isinstance(shape,shapeClass): result.append(shape) return result Is this a valid use of the isinstance function? Is there another way I can do this which might be more pythonic?

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• Checking if an object is inside bounds of an isometric chunk

  - by gopgop

  How would I check if an object is inside the bounds of an isometric chunk? for example I have a player and I want to check if its inside the bounds of this isometric chunk. I draw the isometric chunk's tiles using OpenGL Quads. My first try was checking in a square pattern kind of thing: e = object; this = isometric chunk; if (e.getLocation().getX() < this.getLocation().getX()+World.CHUNK_WIDTH*World.TILE_WIDTH && e.getLocation().getX() > this.getLocation().getX()) { if (e.getLocation().getY() > this.getLocation().getY() && e.getLocation().getY() < this.getLocation().getY()+World.CHUNK_HEIGHT*World.TILE_HEIGHT) { return true; } } return false; What happens here is that it checks in a SQUARE around the chunk so not the real isometric bounds. Image example: (THE RED IS WHERE THE PROGRAM CHECKS THE BOUNDS) What I have now: Desired check: Ultimately I want to do the same for each tile in the chunk. EXTRA INFO: Till now what I had in my game is you could only move tile by tile but now I want them to move freely but I still need them to have a tile location so no matter where they are on the tile their tile location will be that certain tile. then when they are inside a different tile's bounding box then their tile location becomes the new tile. Same thing goes with chunks. the player does have an area but the area does not matter in this case. and as long as the X and Y are inside the bounding box then it should return true. they don't have to be completely on the tile.

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• How broad should a computer science/engineering student go?

  - by AskQuestions

  I have less than 2 years of college left and I still don't know what to focus on. But this is not about me, this is about being a future developer. I realize that questions like "Which language should I learn next?" are not really popular, but I think my question is broader than that. I often see people write things like "You have to learn many different things. Being a developer is not about learning one programming language / technology and then doing that for the rest of your life". Well, sure, but it's impossible to really learn everything thoroughly. Does that mean that one should just learn the basics of everything and then learn some things more thoroughly AFTER getting a particular job? I mean, the best way to learn programming is by actually programming stuff... But projects take time. Does an average developer really switch between (for example) being a web developer, doing artificial intelligence and machine learning related stuff and programming close to the hardware? I mean, I know a lot of different things, but I don't feel proficient in any of those things. If I want to find a job as a web developer (that's just an example) after I finish college, shouldn't I do some web related project (maybe using something I still don't know) rather than try to learn functional programming? So, the question is: How broad should a computer science student's field of focus be? One programming language is surely far too narrow, but what is too broad?

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• Question about separating game core engine from game graphics engine...

  - by Conrad Clark

  Suppose I have a SquareObject class, which implements IDrawable, an interface which contains the method void Draw(). I want to separate drawing logic itself from the game core engine. My main idea is to create a static class which is responsible to dispatch actions to the graphic engine. public static class DrawDispatcher<T> { private static Action<T> DrawAction = new Action<T>((ObjectToDraw)=>{}); public static void SetDrawAction(Action<T> action) { DrawAction = action; } public static void Dispatch(this T Obj) { DrawAction(Obj); } } public static class Extensions { public static void DispatchDraw<T>(this object Obj) { DrawDispatcher<T>.DispatchDraw((T)Obj); } } Then, on the core side: public class SquareObject: GameObject, IDrawable { #region Interface public void Draw() { this.DispatchDraw<SquareObject>(); } #endregion } And on the graphics side: public static class SquareRender{ //stuff here public static void Initialize(){ DrawDispatcher<SquareObject>.SetDrawAction((Square)=>{//my square rendering logic}); } } Do this "pattern" follow best practices? And a plus, I could easily change the render scheme of each object by changing the DispatchDraw parameter, as in: public class SuperSquareObject: GameObject, IDrawable { #region Interface public void Draw() { this.DispatchDraw<SquareObject>(); } #endregion } public class RedSquareObject: GameObject, IDrawable { #region Interface public void Draw() { this.DispatchDraw<RedSquareObject>(); } #endregion } RedSquareObject would have its own render method, but SuperSquareObject would render as a normal SquareObject I'm just asking because i do not want to reinvent the wheel, and there may be a design pattern similar (and better) to this that I may be not acknowledged of. Thanks in advance!

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• Auto-hydrate your objects with ADO.NET

  - by Jake Rutherford

  Recently while writing the monotonous code for pulling data out of a DataReader to hydrate some objects in an application I suddenly wondered "is this really necessary?" You've probably asked yourself the same question, and many of you have: - Used a code generator - Used a ORM such as Entity Framework - Wrote the code anyway because you like busy work     In most of the cases I've dealt with when making a call to a stored procedure the column names match up with the properties of the object I am hydrating. Sure that isn't always the case, but most of the time it's 1 to 1 mapping.  Given that fact I whipped up the following method of hydrating my objects without having write all of the code. First I'll show the code, and then explain what it is doing.      /// <summary>     /// Abstract base class for all Shared objects.     /// </summary>     /// <typeparam name="T"></typeparam>     [Serializable, DataContract(Name = "{0}SharedBase")]     public abstract class SharedBase<T> where T : SharedBase<T>     {         private static List<PropertyInfo> cachedProperties;         /// <summary>         /// Hydrates derived class with values from record.         /// </summary>         /// <param name="dataRecord"></param>         /// <param name="instance"></param>         public static void Hydrate(IDataRecord dataRecord, T instance)         {             var instanceType = instance.GetType();                         //Caching properties to avoid repeated calls to GetProperties.             //Noticable performance gains when processing same types repeatedly.             if (cachedProperties == null)             {                 cachedProperties = instanceType.GetProperties().ToList();             }                         foreach (var property in cachedProperties)             {                 if (!dataRecord.ColumnExists(property.Name)) continue;                 var ordinal = dataRecord.GetOrdinal(property.Name);                 var isNullable = property.PropertyType.IsGenericType &&                                  property.PropertyType.GetGenericTypeDefinition() == typeof (Nullable<>);                 var isNull = dataRecord.IsDBNull(ordinal);                 var propertyType = property.PropertyType;                 if (isNullable)                 {                     if (!string.IsNullOrEmpty(propertyType.FullName))                     {                         var nullableType = Type.GetType(propertyType.FullName);                         propertyType = nullableType != null ? nullableType.GetGenericArguments()[0] : propertyType;                     }                 }                 switch (Type.GetTypeCode(propertyType))                 {                     case TypeCode.Int32:                         property.SetValue(instance,                                           (isNullable && isNull) ? (int?) null : dataRecord.GetInt32(ordinal), null);                         break;                     case TypeCode.Double:                         property.SetValue(instance,                                           (isNullable && isNull) ? (double?) null : dataRecord.GetDouble(ordinal),                                           null);                         break;                     case TypeCode.Boolean:                         property.SetValue(instance,                                           (isNullable && isNull) ? (bool?) null : dataRecord.GetBoolean(ordinal),                                           null);                         break;                     case TypeCode.String:                         property.SetValue(instance, (isNullable && isNull) ? null : isNull ? null : dataRecord.GetString(ordinal),                                           null);                         break;                     case TypeCode.Int16:                         property.SetValue(instance,                                           (isNullable && isNull) ? (int?) null : dataRecord.GetInt16(ordinal), null);                         break;                     case TypeCode.DateTime:                         property.SetValue(instance,                                           (isNullable && isNull)                                               ? (DateTime?) null                                               : dataRecord.GetDateTime(ordinal), null);                         break;                 }             }         }     }   Here is a class which utilizes the above: [Serializable] [DataContract] public class foo : SharedBase<foo> {     [DataMember]     public int? ID { get; set; }     [DataMember]     public string Name { get; set; }     [DataMember]     public string Description { get; set; }     [DataMember]     public string Subject { get; set; }     [DataMember]     public string Body { get; set; }            public foo(IDataRecord record)     {         Hydrate(record, this);                }     public foo() {} }   Explanation: - Class foo inherits from SharedBase specifying itself as the type. (NOTE SharedBase is abstract here in the event we want to provide additional methods which could be overridden by the instance class) public class foo : SharedBase<foo> - One of the foo class constructors accepts a data record which then calls the Hydrate method on SharedBase passing in the record and itself. public foo(IDataRecord record) {      Hydrate(record, this); } - Hydrate method on SharedBase will use reflection on the object passed in to determine its properties. At the same time, it will effectively cache these properties to avoid repeated expensive reflection calls public static void Hydrate(IDataRecord dataRecord, T instance) {      var instanceType = instance.GetType();      //Caching properties to avoid repeated calls to GetProperties.      //Noticable performance gains when processing same types repeatedly.      if (cachedProperties == null)      {           cachedProperties = instanceType.GetProperties().ToList();      } . . . - Hydrate method on SharedBase will iterate each property on the object and determine if a column with matching name exists in data record foreach (var property in cachedProperties) {      if (!dataRecord.ColumnExists(property.Name)) continue;      var ordinal = dataRecord.GetOrdinal(property.Name); . . . NOTE: ColumnExists is an extension method I put on IDataRecord which I’ll include at the end of this post. - Hydrate method will determine if the property is nullable and whether the value in the corresponding column of the data record has a null value var isNullable = property.PropertyType.IsGenericType && property.PropertyType.GetGenericTypeDefinition() == typeof (Nullable<>); var isNull = dataRecord.IsDBNull(ordinal); var propertyType = property.PropertyType; . . .  - If Hydrate method determines the property is nullable it will determine the underlying type and set propertyType accordingly - Hydrate method will set the value of the property based upon the propertyType   That’s it!!!   The magic here is in a few places. First, you may have noticed the following: public abstract class SharedBase<T> where T : SharedBase<T> This says that SharedBase can be created with any type and that for each type it will have it’s own instance. This is important because of the static members within SharedBase. We want this behavior because we are caching the properties for each type. If we did not handle things in this way only 1 type could be cached at a time, or, we’d need to create a collection that allows us to cache the properties for each type = not very elegant.   Second, in the constructor for foo you may have noticed this (literally): public foo(IDataRecord record) {      Hydrate(record, this); } I wanted the code for auto-hydrating to be as simple as possible. At first I wasn’t quite sure how I could call Hydrate on SharedBase within an instance of the class and pass in the instance itself. Fortunately simply passing in “this” does the trick. I wasn’t sure it would work until I tried it out, and fortunately it did.   So, to actually use this feature when utilizing ADO.NET you’d do something like the following:        public List<foo> GetFoo(int? fooId)         {             List<foo> fooList;             const string uspName = "usp_GetFoo";             using (var conn = new SqlConnection(_dbConnection))             using (var cmd = new SqlCommand(uspName, conn))             {                 cmd.CommandType = CommandType.StoredProcedure;                 cmd.Parameters.Add(new SqlParameter("@FooID", SqlDbType.Int)                                        {Direction = ParameterDirection.Input, Value = fooId});                 conn.Open();                 using (var dr = cmd.ExecuteReader())                 {                     fooList= (from row in dr.Cast<DbDataRecord>()                                             select                                                 new foo(row)                                            ).ToList();                 }             }             return fooList;         }   Nice! Instead of having line after line manually assigning values from data record to an object you simply create a new instance and pass in the data record. Note that there are certainly instances where columns returned from stored procedure do not always match up with property names. In this scenario you can still use the above method and simply do your manual assignments afterward.

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• Does your programming knowledge decrease if you don't practice?

  - by Codereview

  I'm a beginner programmer, I study languages such as C/C++/Python and Java (Mainly focused on C++). I'm What you'd call "Young and inexperienced" and I admit that because I can't claim otherwise. As a student I have many other problems besides programming.I practice programming as often as I can, and especially because my teacher gives me a lot more exercises than the rest of the class (It's a very low level), so oftentimes I spend weeks doing something else such as school projects or sports, or travelling, anything besides programming. Don't get me wrong though, I love programming, I love to build functional code, to watch as a program comes alive at the push of a button and to learn as much as I can - I simply don't have much time for it. Straight to the question, now: does your programming knowledge decrease as time passes and you don't practice? You may ask "How much time do you mean?". I don't mean a specific amount of time, but for reference you could take a month-two or even a year as an example. By knowledge I mean anything: From syntax to language functionality.

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• Parsing mathematical experssions with two values that have parenthesis and minus signs

  - by user45921

  I'm trying to parse equations like these which only has two values or the square root of a certain value from a text file: 100+100 -100-100 -(100)+(-100) sqrt(100) by the minues signs, parenthesis and the operator symbol in the middle and the square root, and I have no idea how to start off... I've got the file part done and the simple calculation parts except that I couldnt get my program to solve the equations in the above. #include <stdio.h> #include <string.h> #include <stdlib.h> #include <math.h> main(){ FILE *fp; char buff[255], sym,sym2,del1,del2,del3,del4; double num1, num2; int ret; fp = fopen("input.txt","r"); while(fgets(buff,sizeof(buff),fp)!=NULL){ char *tok = buff; sscanf(tok,"%lf%c%lf",&num1,&sym,&num2); switch(sym){ case '+': printf("%lf\n", num1+num2); break; case '-': printf("%lf\n", num1-num2); break; case '*': printf("%lf\n", num1*num2); break; case '/': printf("%lf\n", num1/num2); break; default: printf("The input value is not correct\n"); break; } } fclose(fp); } that is what have I written for the other basic operations without parenthesis and the minus sign for the second value and it works great for the simple ones. I'm using a switch method to calculate the add, sub, mul and divide but I'm not sure how to properly use the sscanf function (if I am not using it properly) or if there is another way using a function like strtok to properly parse the parenthesis and the minus signs. Any kind help?

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• How can I learn more about ADF?

  - by jhpierce -Oracle

  Look to the Oracle Technology Network for a wealth of information, tutorials, best practices and coding examples. The place to start is the Oracle Application Development Framework (ADF) web page. The Oracle ADF page has basic information and downloads for ADF, but the real wealth is in the links to other pages. One of the pages is the Oracle ADF Code Corner,  which is a blog-style column that provides hints, tips and coding examples for ADF developers. The content on this page ranges from easy to complex and often contains advanced programming concepts. The content is inspired by questions asked on the Oracle JDeveloper customer forum on OTN. The ADF Code Corner has many articles that will inspire your imagination and possibly solve your coding problem.How about the Oracle ADF Architecture Square link? The Oracle ADF Architecture Square focuses on architectural issues and developer guidelines for writing ADF software solutions. The goal is to give ADF developers an understanding of the necessary decisions for building a successful ADF application, to offer potential architectural blueprints to choose from when putting the ADF application together, and to provide potential ADF best practices to take back to your development team. The Oracle ADF Mobile link gives information on developing mobile applications for iOS and Android based applications. There are links to ADF Mobile Overview, ADF Mobile demos and ADF Mobile courses.The Sample ADF Applications link lists sample applications and other resources where you can find code samples for ADF. These are complete ADF applications that can be downloaded into JDeveloper and give you insight into coding an application.There are many more links found under the "Learn More" tab that can equip the developer with the knowledge they need to develop their applications. There are links to overview papers, technical resources, related topics and available training. The information you need IS just a click away.

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• What could cause a sudden stop in Box2D?

  - by alexanderpine

  I'm using Box2d for a game, and I have a bug that's driving me nuts. I've simplified the situation down to a square player sliding back and forth frictionlessly on top of a floor composed of a series of square tiles, driven by the left and right keys (which apply a horizontal force). Works great, sliding back and forth across the whole floor. Except... Every once in a while, the player will suddenly stick at the edge of one of the tiles as if it is hitting a (nonexistent) wall. Further pushes in the same direction it was traveling will fail, but as soon as I push backwards once in the opposite direction, I can push forwards past the sticking point again. The sticking point seems to be random, except for being on the edge of a tile. Happens while going left or right. For debugging purposes, I keep the Positions/velocity values for the previous two update ticks and print them out when this stop occurs. As an example, here you see the player moving right, decelerating slightly; pos2 should be about 8.7, but it stops dead instead. tick0: pos= 8.4636 vel= 7.1875 tick1: pos= 8.5816 vel= 7.0833 tick2: pos= 8.5816 vel= 0.0000 So, as the player is 0.8 and the tiles 1.0 wide, the player is stopping just as it is about to cross onto the next tile (8.5816 + 0.8/2 = 8.9816). In fact, I get a collision message (which I ignore except noting that it happened). It only seems to happen at x.5816 (or -x.4184) while moving right, and x.4167 (or -x.5833) while moving left I said that it's like hitting a wall, but in fact, when it hits a wall, the numbers look more like: tick0: pos0= 12.4131 vel2= 8.4375 tick1: pos1= 12.5555 vel1= 8.5417 tick2: pos2= 12.5850 vel0= 0.0000 so it moves further right on the last tick, which puts it in contact with the wall. Anyone seen anything like this. Any suggestion on how I could be causing this behavior.

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• One sentence descriptions of the various common software licenses?

  - by Rich

  Instead of having to read entire documentation and sift through all the legalese, can someone outline the more common licenses in language that is short and sweet and gets right to the point? Specifically, I'm using a 3rd party control that uses the Apache 2.0 license. My intention is to use this in a proprietary application that I am building for a corporation's use (not resold, but I'm being paid for my work). Does this mean I can or cannot use this control? Does it mean that I must maintain copyright/license information in my code? Does it mean that I must mention copyright/license information in a clearly visible location in the app? EDIT In response to an answer below with a link to an article by Jeff Atwood, the Apache license is described as follows: Apache License Open Permissive 9 Requires derivative works to provide notification of any licensed or proprietary code in a common location. Does this notification need to be in a "common location" in my source code or a common location visible within the app? What if this were a non GUI app (I'm assuming that could very well be my answer)? Thanks for the responses!!!

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• Network(ing) to the Limit

  - by Oracle OpenWorld Blog Team

   By Karen Shamban While Oracle OpenWorld attendees are networking, there's an Oracle Global IT team that builds and maintains the massive networks that help run the show. The objective? To keep things running as seamlessly and smoothly as possible, constantly evaluate priorities, mitigate risk, and be ready for whatever might happen -- because things do happen when there are 50,000 plus attendees, tens of thousands of devices, unexpected requirements, and a constant flow of up-to-the-minute information. Here's just some of what it takes to keep the conference going, network style: 100 Oracle network, voice, and desktop engineers; security, risk management, and other IT experts, who come in from 17 countries  1000+ network switches 300+ miles of copper and fiber 485 wireless access points 2,500 wired laptops 300 VoIP phones And just where are all these networks and devices deployed? This is what the team had to build and manage: Moscone North, South, and West, including: The keynote hall Oracle DEMOgrounds in the Exhibition Halls Hundreds of session rooms Connection Centers, Social Avenue, Lounges Registration The Howard Street Tent and Taylor Street Cafe tented venues Oracle Square (Union Square) Yerba Buena Gardens Masonic Auditorium Sessions and demos at 8 hotel venues That's a whole lot of networking going on. And here's the kicker: the team has only 4 days to bring get it all up and running across these many venues, and exactly 12 hours to take it all down once the show ends. The Global IT team puts in the equivalent of 152 24-hour days for set-up, 227 24-hour days of support during the conferences, and then tears it all down in about 20 24-hour days. And in case you were wondering, the planning for next year's Oracle OpenWorld starts ... next week. No rest for the weary.  Now THAT's networking!  So hats off to the Global IT team -- the job ain't easy, but somebody's got to do it, and they do it remarkably well.

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• l2tp / ipsec debian Openswan U2.6.38 does not connect

  - by locojay

  i am trying to get ipsec/l2tp running on a debian server with an iphone as a client but always get: Dec 2 21:00:04 vpn pluto[22711]: packet from <clientip>:43598: received Vendor ID payload [RFC 3947] method set to=115 Dec 2 21:00:04 vpn pluto[22711]: packet from <clientip>:43598: received Vendor ID payload [draft-ietf-ipsec-nat-t-ike] meth=114, but already using method 115 Dec 2 21:00:04 vpn pluto[22711]: packet from <clientip>:43598: received Vendor ID payload [draft-ietf-ipsec-nat-t-ike-08] meth=113, but already using method 115 Dec 2 21:00:04 vpn pluto[22711]: packet from <clientip>:43598: received Vendor ID payload [draft-ietf-ipsec-nat-t-ike-07] meth=112, but already using method 115 Dec 2 21:00:04 vpn pluto[22711]: packet from <clientip>:43598: received Vendor ID payload [draft-ietf-ipsec-nat-t-ike-06] meth=111, but already using method 115 Dec 2 21:00:04 vpn pluto[22711]: packet from <clientip>:43598: received Vendor ID payload [draft-ietf-ipsec-nat-t-ike-05] meth=110, but already using method 115 Dec 2 21:00:04 vpn pluto[22711]: packet from <clientip>:43598: received Vendor ID payload [draft-ietf-ipsec-nat-t-ike-04] meth=109, but already using method 115 Dec 2 21:00:04 vpn pluto[22711]: packet from <clientip>:43598: received Vendor ID payload [draft-ietf-ipsec-nat-t-ike-03] meth=108, but already using method 115 Dec 2 21:00:04 vpn pluto[22711]: packet from <clientip>:43598: received Vendor ID payload [draft-ietf-ipsec-nat-t-ike-02] meth=107, but already using method 115 Dec 2 21:00:04 vpn pluto[22711]: packet from <clientip>:43598: received Vendor ID payload [draft-ietf-ipsec-nat-t-ike-02_n] meth=106, but already using method 115 Dec 2 21:00:04 vpn pluto[22711]: packet from <clientip>:43598: ignoring Vendor ID payload [FRAGMENTATION 80000000] Dec 2 21:00:04 vpn pluto[22711]: packet from <clientip>:43598: received Vendor ID payload [Dead Peer Detection] Dec 2 21:00:04 vpn pluto[22711]: "L2TP-PSK-noNAT"[4] <clientip> #20: responding to Main Mode from unknown peer <clientip> Dec 2 21:00:04 vpn pluto[22711]: "L2TP-PSK-noNAT"[4] <clientip> #20: transition from state STATE_MAIN_R0 to state STATE_MAIN_R1 Dec 2 21:00:04 vpn pluto[22711]: "L2TP-PSK-noNAT"[4] <clientip> #20: STATE_MAIN_R1: sent MR1, expecting MI2 Dec 2 21:00:04 vpn pluto[22711]: "L2TP-PSK-noNAT"[4] <clientip> #20: NAT-Traversal: Result using draft-ietf-ipsec-nat-t-ike (MacOS X): both are NATed Dec 2 21:00:04 vpn pluto[22711]: "L2TP-PSK-noNAT"[4] <clientip> #20: transition from state STATE_MAIN_R1 to state STATE_MAIN_R2 Dec 2 21:00:04 vpn pluto[22711]: "L2TP-PSK-noNAT"[4] <clientip> #20: STATE_MAIN_R2: sent MR2, expecting MI3 Dec 2 21:00:04 vpn pluto[22711]: "L2TP-PSK-noNAT"[4] <clientip> #20: ignoring informational payload, type IPSEC_INITIAL_CONTACT msgid=00000000 Dec 2 21:00:04 vpn pluto[22711]: "L2TP-PSK-noNAT"[4] <clientip> #20: Main mode peer ID is ID_IPV4_ADDR: '10.2.210.176' Dec 2 21:00:04 vpn pluto[22711]: "L2TP-PSK-noNAT"[4] <clientip> #20: switched from "L2TP-PSK-noNAT" to "L2TP-PSK-noNAT" Dec 2 21:00:04 vpn pluto[22711]: "L2TP-PSK-noNAT"[5] <clientip> #20: deleting connection "L2TP-PSK-noNAT" instance with peer <clientip> {isakmp=#0/ipsec=#0} Dec 2 21:00:04 vpn pluto[22711]: "L2TP-PSK-noNAT"[5] <clientip> #20: transition from state STATE_MAIN_R2 to state STATE_MAIN_R3 Dec 2 21:00:04 vpn pluto[22711]: "L2TP-PSK-noNAT"[5] <clientip> #20: new NAT mapping for #20, was <clientip>:43598, now <clientip>:49826 Dec 2 21:00:04 vpn pluto[22711]: "L2TP-PSK-noNAT"[5] <clientip> #20: STATE_MAIN_R3: sent MR3, ISAKMP SA established {auth=OAKLEY_PRESHARED_KEY cipher=aes_256 prf=oakley_sha group=modp1024} Dec 2 21:00:04 vpn pluto[22711]: "L2TP-PSK-noNAT"[5] <clientip> #20: Dead Peer Detection (RFC 3706): enabled Dec 2 21:00:05 vpn pluto[22711]: "L2TP-PSK-noNAT"[5] <clientip> #20: the peer proposed: <public ip>/32:17/1701 -> 10.2.210.176/32:17/0 Dec 2 21:00:05 vpn pluto[22711]: "L2TP-PSK-noNAT"[5] <clientip> #20: NAT-Traversal: received 2 NAT-OA. using first, ignoring others Dec 2 21:00:05 vpn pluto[22711]: "L2TP-PSK-noNAT"[5] <clientip> #21: responding to Quick Mode proposal {msgid:311d3282} Dec 2 21:00:05 vpn pluto[22711]: "L2TP-PSK-noNAT"[5] <clientip> #21: us: 171.138.2.13<171.138.2.13>:17/1701 Dec 2 21:00:05 vpn pluto[22711]: "L2TP-PSK-noNAT"[5] <clientip> #21: them: <clientip>[10.2.210.176]:17/61719 Dec 2 21:00:05 vpn pluto[22711]: "L2TP-PSK-noNAT"[5] <clientip> #21: transition from state STATE_QUICK_R0 to state STATE_QUICK_R1 Dec 2 21:00:05 vpn pluto[22711]: "L2TP-PSK-noNAT"[5] <clientip> #21: STATE_QUICK_R1: sent QR1, inbound IPsec SA installed, expecting QI2 Dec 2 21:00:05 vpn pluto[22711]: "L2TP-PSK-noNAT"[5] <clientip> #21: Dead Peer Detection (RFC 3706): enabled Dec 2 21:00:05 vpn pluto[22711]: "L2TP-PSK-noNAT"[5] <clientip> #21: transition from state STATE_QUICK_R1 to state STATE_QUICK_R2 Dec 2 21:00:05 vpn pluto[22711]: "L2TP-PSK-noNAT"[5] <clientip> #21: STATE_QUICK_R2: IPsec SA established transport mode {ESP=>0x05e23c9a <0x216077a9 xfrm=AES_256-HMAC_SHA1 NATOA=10.2.210.176 NATD=<clientip>:49826 DPD=enabled} Dec 2 21:00:26 vpn pluto[22711]: "L2TP-PSK-noNAT"[5] <clientip> #20: received Delete SA(0x05e23c9a) payload: deleting IPSEC State #21 Dec 2 21:00:26 vpn pluto[22711]: "L2TP-PSK-noNAT"[5] <clientip> #20: received and ignored informational message Dec 2 21:00:27 vpn pluto[22711]: "L2TP-PSK-noNAT"[5] <clientip> #20: received Delete SA payload: deleting ISAKMP State #20 Dec 2 21:00:27 vpn pluto[22711]: "L2TP-PSK-noNAT"[5] <clientip>: deleting connection "L2TP-PSK-noNAT" instance with peer <clientip> {isakmp=#0/ipsec=#0} Dec 2 21:00:27 vpn pluto[22711]: packet from <clientip>:49826: received and ignored informational message Dec 2 21:00:27 vpn pluto[22711]: ERROR: asynchronous network error report on eth0 (sport=4500) for message to <clientip> port 49826, complainant <clientip>: Connection refused [errno 111, origin ICMP type 3 code 3 (not authenticated)] my setup looks like this verizon fios actiontec -- DMZ-- ddwrt router -- debian xen instance actiontec : 192.168.1.1 ddwrt: 171.138.2.1 debian xen server: 171.138.2.13 forwarded udp 500, 4500, 1701 on ddwrt to debian xen instance. vpn passthrough is enabled /etc/ipsec.conf config setup dumpdir=/var/run/pluto/ nat_traversal=yes virtual_private=%v4:10.0.0.0/8,%v4:192.168.0.0/16,%v4:172.16.0.0/12,%v4:25.0.0.0/8,%v6:fd00::/8,%v6:fe80::/10,%v4:!171.138.2.0/24,%v4:!192.168.1.0/24 protostack=netkey # Add connections here conn L2TP-PSK-NAT rightsubnet=vhost:%priv also=L2TP-PSK-noNAT conn L2TP-PSK-noNAT authby=secret pfs=no auto=add keyingtries=3 # we cannot rekey for %any, let client rekey rekey=no # Apple iOS doesn't send delete notify so we need dead peer detection # to detect vanishing clients dpddelay=30 dpdtimeout=120 dpdaction=clear # Set ikelifetime and keylife to same defaults windows has ikelifetime=8h keylife=1h # l2tp-over-ipsec is transport mode type=transport # left=171.138.2.13 # # For updated Windows 2000/XP clients, # to support old clients as well, use leftprotoport=17/%any leftprotoport=17/1701 # # The remote user. # right=%any # Using the magic port of "%any" means "any one single port". This is # a work around required for Apple OSX clients that use a randomly # high port. rightprotoport=17/%any #force all to be nat'ed. because of ios conn passthrough-for-non-l2tp type=passthrough left=171.138.2.13 leftnexthop=171.138.2.1 right=0.0.0.0 rightsubnet=0.0.0.0/0 auto=route /etc/xl2tp/xl2tp.conf [global] ipsec saref = no listen-addr = 171.138.2.13 ;port = 1701 ;debug network = yes ;debug tunnel = yes ;debug network = yes ;debug packet = yes [lns default] ip range = 171.138.2.231-171.138.2.239 local ip = 171.138.2.13 assign ip = yes require chap = no refuse pap = no require authentication = no ;name = OpenswanVPN ppp debug = yes pppoptfile = /etc/ppp/options.xlt2tpd lenght bit = yes /etc/ppp/options.xl2tpd ;require-mschap-v2 pcp-accept-local ipcp-accept-local ipcp-accept-remote ;ms-dns 171.138.2.1 ms-dns 192.168.1.1 ms-dns 8.8.8.8 name l2tpd noccp auth crtscts idle 1800 mtu 1410 mru 1410 lock proxyarp connect-delay 5000 debug dump logfd 2 logfile /var/log/xl2tpd.log ipsec verify Checking your system to see if IPsec got installed and started correctly: Version check and ipsec on-path [OK] Linux Openswan U2.6.38/K3.0.0-1-amd64 (netkey) Checking for IPsec support in kernel [OK] SAref kernel support [N/A] NETKEY: Testing XFRM related proc values [OK] [OK] [OK] Checking that pluto is running [OK] Pluto listening for IKE on udp 500 [OK] Pluto listening for NAT-T on udp 4500 [OK] Two or more interfaces found, checking IP forwarding [FAILED] Checking NAT and MASQUERADEing [OK] Checking for 'ip' command [OK] Checking /bin/sh is not /bin/dash [WARNING] Checking for 'iptables' command [OK] Opportunistic Encryption Support [DISABLED] The failed can be ignored i guess since cat /proc/sys/net/ipv4/ip_forward returns 1 any help would be much appreciated as i don't have any idea why this is not working

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• JSON error Caused by: java.lang.NullPointerException

  - by user3821853

  im trying to make a register page on android using JSON. everytime i press register button on avd, i get an error "unfortunately database has stopped". i have a error on my logcat that i cannot understand. this my code. please someone help me. this my register.java import android.app.Activity; import android.app.ProgressDialog; import android.os.AsyncTask; import android.os.Bundle; import android.util.Log; import android.view.View; import android.view.View.OnClickListener; import android.widget.Button; import android.widget.EditText; import android.widget.Toast; import org.apache.http.NameValuePair; import org.apache.http.message.BasicNameValuePair; import org.json.JSONException; import org.json.JSONObject; import java.util.ArrayList; import java.util.List; public class Register extends Activity implements OnClickListener{ private EditText user, pass; private Button mRegister; // Progress Dialog private ProgressDialog pDialog; // JSON parser class JSONParser jsonParser = new JSONParser(); //php register script //localhost : //testing on your device //put your local ip instead, on windows, run CMD > ipconfig //or in mac's terminal type ifconfig and look for the ip under en0 or en1 // private static final String REGISTER_URL = "http://xxx.xxx.x.x:1234/webservice/register.php"; //testing on Emulator: private static final String REGISTER_URL = "http://10.0.2.2:1234/webservice/register.php"; //testing from a real server: //private static final String REGISTER_URL = "http://www.mybringback.com/webservice/register.php"; //ids private static final String TAG_SUCCESS = "success"; private static final String TAG_MESSAGE = "message"; @Override protected void onCreate(Bundle savedInstanceState) { // TODO Auto-generated method stub super.onCreate(savedInstanceState); setContentView(R.layout.register); user = (EditText)findViewById(R.id.username); pass = (EditText)findViewById(R.id.password); mRegister = (Button)findViewById(R.id.register); mRegister.setOnClickListener(this); } @Override public void onClick(View v) { // TODO Auto-generated method stub new CreateUser().execute(); } class CreateUser extends AsyncTask<String, String, String> { @Override protected void onPreExecute() { super.onPreExecute(); pDialog = new ProgressDialog(Register.this); pDialog.setMessage("Creating User..."); pDialog.setIndeterminate(false); pDialog.setCancelable(true); pDialog.show(); } @Override protected String doInBackground(String... args) { // TODO Auto-generated method stub // Check for success tag int success; String username = user.getText().toString(); String password = pass.getText().toString(); try { // Building Parameters List<NameValuePair> params = new ArrayList<NameValuePair>(); params.add(new BasicNameValuePair("username", username)); params.add(new BasicNameValuePair("password", password)); Log.d("request!", "starting"); //Posting user data to script JSONObject json = jsonParser.makeHttpRequest( REGISTER_URL, "POST", params); // full json response Log.d("Registering attempt", json.toString()); // json success element success = json.getInt(TAG_SUCCESS); if (success == 1) { Log.d("User Created!", json.toString()); finish(); return json.getString(TAG_MESSAGE); }else{ Log.d("Registering Failure!", json.getString(TAG_MESSAGE)); return json.getString(TAG_MESSAGE); } } catch (JSONException e) { e.printStackTrace(); } return null; } protected void onPostExecute(String file_url) { // dismiss the dialog once product deleted pDialog.dismiss(); if (file_url != null){ Toast.makeText(Register.this, file_url, Toast.LENGTH_LONG).show(); } } } } this is JSONparser.java import android.util.Log; import org.apache.http.HttpEntity; import org.apache.http.HttpResponse; import org.apache.http.NameValuePair; import org.apache.http.client.ClientProtocolException; import org.apache.http.client.entity.UrlEncodedFormEntity; import org.apache.http.client.methods.HttpGet; import org.apache.http.client.methods.HttpPost; import org.apache.http.client.utils.URLEncodedUtils; import org.apache.http.impl.client.DefaultHttpClient; import org.json.JSONException; import org.json.JSONObject; import java.io.BufferedReader; import java.io.IOException; import java.io.InputStream; import java.io.InputStreamReader; import java.io.UnsupportedEncodingException; import java.util.List; public class JSONParser { static InputStream is = null; static JSONObject jObj = null; static String json = ""; // constructor public JSONParser() { } public JSONObject getJSONFromUrl(final String url) { // Making HTTP request try { // Construct the client and the HTTP request. DefaultHttpClient httpClient = new DefaultHttpClient(); HttpPost httpPost = new HttpPost(url); // Execute the POST request and store the response locally. HttpResponse httpResponse = httpClient.execute(httpPost); // Extract data from the response. HttpEntity httpEntity = httpResponse.getEntity(); // Open an inputStream with the data content. is = httpEntity.getContent(); } catch (UnsupportedEncodingException e) { e.printStackTrace(); } catch (ClientProtocolException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } try { // Create a BufferedReader to parse through the inputStream. BufferedReader reader = new BufferedReader(new InputStreamReader( is, "iso-8859-1"), 8); // Declare a string builder to help with the parsing. StringBuilder sb = new StringBuilder(); // Declare a string to store the JSON object data in string form. String line = null; // Build the string until null. while ((line = reader.readLine()) != null) { sb.append(line + "\n"); } // Close the input stream. is.close(); // Convert the string builder data to an actual string. json = sb.toString(); } catch (Exception e) { Log.e("Buffer Error", "Error converting result " + e.toString()); } // Try to parse the string to a JSON object try { jObj = new JSONObject(json); } catch (JSONException e) { Log.e("JSON Parser", "Error parsing data " + e.toString()); } // Return the JSON Object. return jObj; } // function get json from url // by making HTTP POST or GET mehtod public JSONObject makeHttpRequest(String url, String method, List<NameValuePair> params) { // Making HTTP request try { // check for request method if(method == "POST"){ // request method is POST // defaultHttpClient DefaultHttpClient httpClient = new DefaultHttpClient(); HttpPost httpPost = new HttpPost(url); httpPost.setEntity(new UrlEncodedFormEntity(params)); HttpResponse httpResponse = httpClient.execute(httpPost); HttpEntity httpEntity = httpResponse.getEntity(); is = httpEntity.getContent(); }else if(method == "GET"){ // request method is GET DefaultHttpClient httpClient = new DefaultHttpClient(); String paramString = URLEncodedUtils.format(params, "utf-8"); url += "?" + paramString; HttpGet httpGet = new HttpGet(url); HttpResponse httpResponse = httpClient.execute(httpGet); HttpEntity httpEntity = httpResponse.getEntity(); is = httpEntity.getContent(); } } catch (UnsupportedEncodingException e) { e.printStackTrace(); } catch (ClientProtocolException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } try { BufferedReader reader = new BufferedReader(new InputStreamReader( is, "iso-8859-1"), 8); StringBuilder sb = new StringBuilder(); String line = null; while ((line = reader.readLine()) != null) { sb.append(line + "\n"); } is.close(); json = sb.toString(); } catch (Exception e) { Log.e("Buffer Error", "Error converting result " + e.toString()); } // try parse the string to a JSON object try { jObj = new JSONObject(json); } catch (JSONException e) { Log.e("JSON Parser", "Error parsing data " + e.toString()); } // return JSON String return jObj; } } and this my error 08-18 23:40:02.381 2000-2018/com.example.blackcustomzier.database E/Buffer Error? Error converting result java.lang.NullPointerException: lock == null 08-18 23:40:02.381 2000-2018/com.example.blackcustomzier.database E/JSON Parser? Error parsing data org.json.JSONException: End of input at character 0 of 08-18 23:40:02.391 2000-2018/com.example.blackcustomzier.database W/dalvikvm? threadid=15: thread exiting with uncaught exception (group=0xb0f37648) 08-18 23:40:02.391 2000-2018/com.example.blackcustomzier.database E/AndroidRuntime? FATAL EXCEPTION: AsyncTask #4 java.lang.RuntimeException: An error occured while executing doInBackground() at android.os.AsyncTask$3.done(AsyncTask.java:299) at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:352) at java.util.concurrent.FutureTask.setException(FutureTask.java:219) at java.util.concurrent.FutureTask.run(FutureTask.java:239) at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573) at java.lang.Thread.run(Thread.java:841) Caused by: java.lang.NullPointerException at com.example.blackcustomzier.database.Register$CreateUser.doInBackground(Register.java:108) at com.example.blackcustomzier.database.Register$CreateUser.doInBackground(Register.java:74) at android.os.AsyncTask$2.call(AsyncTask.java:287) at java.util.concurrent.FutureTask.run(FutureTask.java:234)             at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)             at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)             at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)             at java.lang.Thread.run(Thread.java:841) 08-18 23:40:02.501 2000-2000/com.example.blackcustomzier.database W/EGL_emulation? eglSurfaceAttrib not implemented 08-18 23:40:02.591 2000-2000/com.example.blackcustomzier.database W/EGL_emulation? eglSurfaceAttrib not implemented 08-18 23:40:02.981 2000-2000/com.example.blackcustomzier.database E/WindowManager? Activity com.example.blackcustomzier.database.Register has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView{b1294c60 V.E..... R......D 0,0-1026,288} that was originally added here android.view.WindowLeaked: Activity com.example.blackcustomzier.database.Register has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView{b1294c60 V.E..... R......D 0,0-1026,288} that was originally added here at android.view.ViewRootImpl.<init>(ViewRootImpl.java:345) at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:239) at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:69) at android.app.Dialog.show(Dialog.java:281) at com.example.blackcustomzier.database.Register$CreateUser.onPreExecute(Register.java:85) at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:586) at android.os.AsyncTask.execute(AsyncTask.java:534) at com.example.blackcustomzier.database.Register.onClick(Register.java:70) at android.view.View.performClick(View.java:4240) at android.view.View.onKeyUp(View.java:7928) at android.widget.TextView.onKeyUp(TextView.java:5606) at android.view.KeyEvent.dispatch(KeyEvent.java:2647) at android.view.View.dispatchKeyEvent(View.java:7343) at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1393) at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1393) at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1393) at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1393) at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchKeyEvent(PhoneWindow.java:1933) at com.android.internal.policy.impl.PhoneWindow.superDispatchKeyEvent(PhoneWindow.java:1408) at android.app.Activity.dispatchKeyEvent(Activity.java:2384) at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchKeyEvent(PhoneWindow.java:1860) at android.view.ViewRootImpl$ViewPostImeInputStage.processKeyEvent(ViewRootImpl.java:3791) at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:3774) at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3379) at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3429) at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3398) at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:3483) at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3406) at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:3540) at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3379) at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3429) at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3398) at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3406) at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3379) at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3429) at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3398) at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:3516) at android.view.ViewRootImpl$ImeInputStage.onFinishedInputEvent(ViewRootImpl.java:3666) at android.view.inputmethod.InputMethodManager$PendingEvent.run(InputMethodManager.java:1982) at android.view.inputmethod.InputMethodManager.invokeFinishedInputEventCallback(InputMethodManager.java:1698) at android.view.inputmethod.InputMethodManager.finishedInputEvent(InputMethodManager.java:1689) at android.view.inputmethod.InputMethodManager$ImeInputEventSender.onInputEventFinished(InputMethodManager.java:1959) at android.view.InputEventSender.dispatchInputEventFinished(InputEventSender.java:141) at android.os.MessageQueue.nativePollOnce(Native Method) at android.os.MessageQueue.next(MessageQueue.java:132) at android.os.Looper.loop(Looper.java:124) at android.app.ActivityThread.main(ActivityThread.java:5103) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:525) at com.android.internal.os.ZygoteInit$MethodAndArgsCal please help me to solve this thx

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