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• Advice on a good comeback strategy after years of java abstinence

  - by simou

  It's almost 5 yrs since I left the java IT-project/enterprise business. Before I was a highly skilled enterprise developer / OO architect with more than 10 years experience in the business. I was proficient in many of those enterprise related technologies, including DWHing. Since then I haven't been doing any large scale programming, a little bit of C, Python, some dips into Scala, hacking a small java-plugin framework, opengl, but only as fun projects. Now I want to re-enter the java stage again, i.e. I'm looking for job opportunities as a developer. But I fear I might have lost much of my former punching strength, e.g. I would have to give my SQL knowledge a deep refreshing breath, re-visit basic stuff like design patterns, enterprise architectures, etc. and probably learn the new stuff like EJB3.1, JEE 6 too. I also missed the whole scrum craze. So from your own experience, what subject should I tackle first? Like technology (which ones?) or design skills (uml..)? But what I'm also wondering is since the basic design / architectural principles haven't changed much by now, what would be the chance on the job market for someone like me who left the java-world at a time where everything was less fragmented and EJB2.1 and XDoclet were de-facto standards? And how could I convince a potential employer that I'm still an effective on-the-job learner? Should I rather aim for "junior positions" ? Lots of questions but I'd be really glad if you could share your (encouraging :) thoughts with me. cheers! (btw I'm based in Austria)

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• How do NTP Servers Manage to Stay so Accurate?

  - by Akemi Iwaya

  Many of us have had the occasional problem with our computers and other devices retaining accurate time settings, but a quick sync with an NTP server makes all well again. But if our own devices can lose accuracy, how do NTP servers manage to stay so accurate? Today’s Question & Answer session comes to us courtesy of SuperUser—a subdivision of Stack Exchange, a community-driven grouping of Q&A web sites. Photo courtesy of LEOL30 (Flickr). The Question SuperUser reader Frank Thornton wants to know how NTP servers are able to remain so accurate: I have noticed that on my servers and other machines, the clocks always drift so that they have to sync up to remain accurate. How do the NTP server clocks keep from drifting and always remain so accurate? How do the NTP servers manage to remain so accurate? The Answer SuperUser contributor Michael Kjorling has the answer for us: NTP servers rely on highly accurate clocks for precision timekeeping. A common time source for central NTP servers are atomic clocks, or GPS receivers (remember that GPS satellites have atomic clocks onboard). These clocks are defined as accurate since they provide a highly exact time reference. There is nothing magical about GPS or atomic clocks that make them tell you exactly what time it is. Because of how atomic clocks work, they are simply very good at, having once been told what time it is, keeping accurate time (since the second is defined in terms of atomic effects). In fact, it is worth noting that GPS time is distinct from the UTC that we are more used to seeing. These atomic clocks are in turn synchronized against International Atomic Time or TAI in order to not only accurately tell the passage of time, but also the time. Once you have an exact time on one system connected to a network like the Internet, it is a matter of protocol engineering enabling transfer of precise times between hosts over an unreliable network. In this regard a Stratum 2 (or farther from the actual time source) NTP server is no different from your desktop system syncing against a set of NTP servers. By the time you have a few accurate times (as obtained from NTP servers or elsewhere) and know the rate of advancement of your local clock (which is easy to determine), you can calculate your local clock’s drift rate relative to the “believed accurate” passage of time. Once locked in, this value can then be used to continuously adjust the local clock to make it report values very close to the accurate passage of time, even if the local real-time clock itself is highly inaccurate. As long as your local clock is not highly erratic, this should allow keeping accurate time for some time even if your upstream time source becomes unavailable for any reason. Some NTP client implementations (probably most ntpd daemon or system service implementations) do this, and others (like ntpd’s companion ntpdate which simply sets the clock once) do not. This is commonly referred to as a drift file because it persistently stores a measure of clock drift, but strictly speaking it does not have to be stored as a specific file on disk. In NTP, Stratum 0 is by definition an accurate time source. Stratum 1 is a system that uses a Stratum 0 time source as its time source (and is thus slightly less accurate than the Stratum 0 time source). Stratum 2 again is slightly less accurate than Stratum 1 because it is syncing its time against the Stratum 1 source and so on. In practice, this loss of accuracy is so small that it is completely negligible in all but the most extreme of cases. Have something to add to the explanation? Sound off in the comments. Want to read more answers from other tech-savvy Stack Exchange users? Check out the full discussion thread here.

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• Google Keyword Research Easy But Powerful - Real Time Results - Real Time Traffic

  The below is not just an information section, it's a job! You have to do something here. You need to take action, don't just read it, and think "OK, this is a good idea, I should do it". You see that word "should" we need to change it to "I WILL".

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• Liskov substitution and abstract classes / strategy pattern

  - by Kolyunya

  I'm trying to follow LSP in practical programming. And I wonder if different constructors of subclasses violate it. It would be great to hear an explanation instead of just yes/no. Thanks much! P.S. If the answer is no, how do I make different strategies with different input without violating LSP? class IStrategy { public: virtual void use() = 0; }; class FooStrategy : public IStrategy { public: FooStrategy(A a, B b) { c = /* some operations with a, b */ } virtual void use() { std::cout << c; } private: C c; }; class BarStrategy : public IStrategy { public: BarStrategy(D d, E e) { f = /* some operations with d, e */ } virtual void use() { std::cout << f; } private: F f; };

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• Deciding on a company-wide javascript strategy [on hold]

  - by drogon

  Our company is moving most of its software from thick-client winforms apps to web apps. We are using asp.net mvc on the server side. Most of the developers are brand new to the web and need to become efficient and knowledgeable at writing client-side web code (javascript). We are deciding on a number of things and would appreciate feedback on the following: Angular.js or Backbone.js? Backbone (w/ Underscore) is certainly more light weight, but requires more custom development. Angular seems to be a full-fledged framework, but would require everyone to embrace it and probably a longer learning curve(??). (Note: I know nothing about Angular at this point) Require.js or script includes w/ MVC bundleconfig? Require.js makes development "feel like" c# (importing namespaces). But, integrating the build/minification process can be a pain (especially the configuration). Bundling via mvc requires developers to worry more about which scripts to include but has less overall development friction. Typescript vs Javascript Regardless of frameworks, our developers are going to need to learn the basics. Typescript is more like c# and MAY be easier for c# developers to understand. However, learning TypeScript before javascript may hinder their mastery of javascript at the expense of efficiency.

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• Real-time chat in Ruby on Rails

  - by Skydreamer

  First, I'm sorry because I know this question has been asked many times but I'm still looking forward to finding the answer to my problem. I'd want to implement a Real-time chat for my Rails app but I can't really host the server which handles the sockets. I've tried Faye but it needs a server. I've also heard of pusher but it's limited to 20 users at a time on the chat and I can't really be sure they won't be more. I've thought of irc but I think I can't really embed it into a rails app, maybe it needs sockets... So here's my problem, can I implement a real-time chat without owning a server ? What can you advice me ? Thank you for your answers.

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• heroku time zone problem, logging local server time

  - by Ole Morten Amundsen

  UPDATE: Ok, I didn't formulate a good Q to be answered. I still struggle with heroku being on -07:00 UTC and I at +02:200 UTC. Q: How do I get the log written in the correct Time.zone ? The 9 hours difference, heroku (us west) - norway, is distracting to work with. I get this in my production.log (using heroku logs): Processing ProductionController#create to xml (for 81.26.51.35 at 2010-04-28 23:00:12) [POST] How do I get it to write 2010-04-29 08:00:12 +02:00 GMT ? Note that I'm running at heroku and cannot set the server time myself, as one could do at your amazon EC2 servers. Below is my previous question, I'll leave it be as it holds some interesting information about time and zones. Why does Time.now yield the server local time when I have set the another time zone in my environment.rb config.time_zone = 'Copenhagen' I've put this in a view <p> Time.zone <%= Time.zone %> </p> <p> Time.now <%= Time.now %> </p> <p> Time.now.utc <%= Time.now.utc %> </p> <p> Time.zone.now <%= Time.zone.now %> </p> <p> Time.zone.today <%= Time.zone.today %> </p> rendering this result on my app at heroku Time.zone (GMT+01:00) Copenhagen Time.now Mon Apr 26 08:28:21 -0700 2010 Time.now.utc Mon Apr 26 15:28:21 UTC 2010 Time.zone.now 2010-04-26 17:28:21 +0200 Time.zone.today 2010-04-26 Time.zone.now yields the correct result. Do I have to switch from Time.now to Time.zone.now, everywhere? Seems cumbersome. I truly don't care what the local time of the server is, it's giving me loads of trouble due to extensive use of Time.now. Am I misunderstanding anything fundamental here?

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• Real time web services

  - by daliz

  Hi everybody, I have a little (maybe the answer could require a book) question about web services and server side programming. But first, a little preamble. Recently we have seen new kind of applications & games using some kind of real-time interaction with a database, or more generally, with other users. I'm talking about shared drawing canvas, games like this , or simple chats, or the Android app "a World of Photo", where in real time you see who is online, to share your photos, etc. Now my question: Are all these apps based on classic TCP client/server architectures or is there a way to make them in a simpler way, like a web platform like LAMP? What I'm asking, in other words is: Can PHP+MySQL (or JSP, or RoR, or any other server language) provide a way to make online users communicate in real time and share data? Is there a way to do that without the ugly and heavy mechanism of temporary tables? Thank you! I hope I've been clear.

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• Is context inheritance, as shown by Head First Design Patterns' Duck example, irrelevant to strategy pattern?

  - by Korey Hinton

  In Head First Design Patterns it teaches the strategy pattern by using a Duck example where different subclasses of Duck can be assigned a particular behavior at runtime. From my understanding the purpose of the strategy pattern is to change an object's behavior at runtime. Emphasis on "an" meaning one. Could I further simplify this example by just having a Duck class (no derived classes)? Then when implementing one duck object it can be assigned different behaviors based on certain circumstances that aren't dependent on its own object type. For example: FlyBehavior changes based on the weather or QuackBehavior changes based on the time of day or how hungry a duck is. Would my example above constitute the strategy pattern as well? Is context inheritance (Duck) irrelevant to the strategy pattern or is that the reason for the strategy pattern? Here is the UML diagram from the Head First book:

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• Using real fonts in HTML 5 & CSS 3 pages

  - by nikolaosk

  This is going to be the fifth post in a series of posts regarding HTML 5. You can find the other posts here, here , here and here.In this post I will provide a hands-on example on how to use real fonts in HTML 5 pages with the use of CSS 3.Font issues have been appearing in all websites and caused all sorts of problems for web designers.The real problem with fonts for web developers until now was that they were forced to use only a handful of fonts.CSS 3 allows web designers not to use only web-safe fonts.These fonts are in wide use in most user's operating systems.Some designers (when they wanted to make their site stand out) resorted in various techniques like using images instead of fonts. That solution is not very accessible-friendly and definitely less SEO friendly.CSS (through CSS3's Fonts module) 3 allows web developers to embed fonts directly on a web page.First we need to define the font and then attach the font to elements.Obviously we have various formats for fonts. Some are supported by all modern browsers and some are not.The most common formats are, Embedded OpenType (EOT),TrueType(TTF),OpenType(OTF). I will use the @font-face declaration to define the font used in this page.  Before you download fonts (in any format) make sure you have understood all the licensing issues. Please note that all these real fonts will be downloaded in the client's computer.A great resource on the web (maybe the best) is http://www.typekit.com/.They have an abundance of web fonts for use. Please note that they sell those fonts.Another free (best things in life a free, aren't they?) resource is the http://www.google.com/webfonts website. I have visited the website and downloaded the Aladin webfont.When you download any font you like make sure you read the license first. Aladin webfont is released under the Open Font License (OFL) license. Before I go on with the actual demo I will use the (http://www.caniuse.com) to see the support for web fonts from the latest versions of modern browsers.Please have a look at the picture below. We see that all the latest versions of modern browsers support this feature. In order to be absolutely clear this is not (and could not be) a detailed tutorial on HTML 5. There are other great resources for that.Navigate to the excellent interactive tutorials of W3School.Another excellent resource is HTML 5 Doctor.Two very nice sites that show you what features and specifications are implemented by various browsers and their versions are http://caniuse.com/ and http://html5test.com/. At this times Chrome seems to support most of HTML 5 specifications.Another excellent way to find out if the browser supports HTML 5 and CSS 3 features is to use the Javascript lightweight library Modernizr.In this hands-on example I will be using Expression Web 4.0.This application is not a free application. You can use any HTML editor you like.You can use Visual Studio 2012 Express edition. You can download it here.I create a simple HTML 5 page. The markup follows and it is very easy to use and understand<!DOCTYPE html><html lang="en">  <head>    <title>HTML 5, CSS3 and JQuery</title>    <meta http-equiv="Content-Type" content="text/html;charset=utf-8" >    <link rel="stylesheet" type="text/css" href="style.css">       </head>  <body>      <div id="header">      <h1>Learn cutting edge technologies</h1>      <p>HTML 5, JQuery, CSS3</p>    </div>        <div id="main">          <h2>HTML 5</h2>                        <p>            HTML5 is the latest version of HTML and XHTML. The HTML standard defines a single language that can be written in HTML and XML. It attempts to solve issues found in previous iterations of HTML and addresses the needs of Web Applications, an area previously not adequately covered by HTML.          </p>      </div>             </body>  </html> Then I create the style.css file.<style type="text/css">@font-face{font-family:Aladin;src: url('Aladin-Regular.ttf')}h1{font-family:Aladin,Georgia,serif;}</style> As you can see we want to style the h1 tag in our HTML 5 markup.I just use the @font-face property,specifying the font-family and the source of the web font. Then I just use the name in the font-family property to style the h1 tag.Have a look below to see my page in IE10. Make sure you open this page in all your browsers installed in your machine. Make sure you have downloaded the latest versions. Now we can make our site stand out with web fonts and give it a really unique look and feel. Hope it helps!!!  

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• JVM system time runs faster than HP UNIX OS system time

  - by winston

  Hello I have the following output from a simple debug jsp: Weblogic Startup Since: Friday, October 19, 2012, 08:36:12 AM Database Current Time: Wednesday, December 12, 2012, 11:43:44 AM Weblogic JVM Current Time: Wednesday, December 12, 2012, 11:45:38 AM Line 1 was a recorded variable during WebLogic webapp startup. Line 2 was output from database query select sysdate from dual; Line 3 was output from java code new Date() I have checked from shell date command that line 2 output conforms with OS time. The output of line 3 was mysterious. I don't know how it comes from Java VM. On another machine with same setting, the same jsp output like this: Weblogic Startup Since: Tuesday, December 11, 2012, 02:29:06 PM Database Current Time: Wednesday, December 12, 2012, 11:51:48 AM Weblogic JVM Current Time: Wednesday, December 12, 2012, 11:51:50 AM Another machine: Weblogic Startup Since: Monday, December 10, 2012, 05:00:34 PM Database Current Time: Wednesday, December 12, 2012, 11:52:03 AM Weblogic JVM Current Time: Wednesday, December 12, 2012, 11:52:07 AM Findings: the pattern shows that the longer Weblogic startup, the larger the discrepancy of OS time with JVM time. Anybody could help on HP JVM? On HP UNIX, NTP was done daily. Anyway here comes the server versions: HP-UX machinex B.11.31 U ia64 2426956366 unlimited-user license java version "1.6.0.04" Java(TM) SE Runtime Environment (build 1.6.0.04-jinteg_28_apr_2009_04_46-b00) Java HotSpot(TM) Server VM (build 11.3-b02-jre1.6.0.04-rc2, mixed mode) WebLogic Server Version: 10.3.2.0 Java properties java.runtime.name=Java(TM) SE Runtime Environment java.runtime.version=1.6.0.04-jinteg_28_apr_2009_04_46-b00 java.vendor=Hewlett-Packard Co. java.vendor.url=http\://www.hp.com/go/Java java.version=1.6.0.04 java.vm.name=Java HotSpot(TM) 64-Bit Server VM java.vm.info=mixed mode java.vm.specification.vendor=Sun Microsystems Inc. java.vm.vendor="Hewlett-Packard Company" sun.arch.data.model=64 sun.cpu.endian=big sun.cpu.isalist=ia64r0 sun.io.unicode.encoding=UnicodeBig sun.java.launcher=SUN_STANDARD sun.jnu.encoding=8859_1 sun.management.compiler=HotSpot 64-Bit Server Compiler sun.os.patch.level=unknown os.name=HP-UX os.version=B.11.31

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• Apple: Time capsule, 2 questions

  - by Patrick

  1) Can I use time capsule as server ? Can I run operating systems on it ? 2) I'm using time machine with my mac with time capsule. Let's say my mac crashes, and I cannot use it anymore. Can i restore my mac disk on another laptop from time capsule ? In other words, can I have a perfect copy of my mac hard disk on another mac ? thanks

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• Windows Media Player - always show Current Time/Total Time

  - by Siim K

  I'm using Windows Media Player 12 on Windows 7. When I open a video file then it by default only shows the current position (time). If I click on it once then it changes to format Current Time / Total Time Is there any way to make this format permanent (registry hack/some setting I have not noticed)? Right now every time I close WMP and open another file it's back to the default (only current time) setting.

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• Spreading incoming batched data into a real-time stream

  - by pr1001

  I would like to display some events in 'real-time'. However, I must fetch the data from another source. I can request the last X minutes, though the source is updated approximately every 5 minutes. This means that there will be a delay between the most recent data retrieved and the point in time that I make the request. Second, because I will be receiving a batch of data, I don't want to just fire out all the events down a socket once my fetcher has retrieved it: I would like to spread out the events so that they are both accurately spaced amongst each other and in sync with their original occurrences (e.g. an event is always displayed 6 minutes after it actually happened). My thought is to fetch the data every 5 minutes from the source, knowing that I won't get the very latest data. The original data would be then queued to be sent down the socket 7.5 minutes from its original timestamp – that is, at least ~2.5 minutes from when its batch was fetched and at most 7.5 minutes since then. My question is this: is this the best way to approach the problem? Does this problem have any standard approaches or associated literature related to implementation best-practices and edge cases? I am a bit worried that the frequency of my fetches and the frequency in which the source is updated will get out of sync, leading to points where no data will be retrieved from the source. However, since my socket delay is greater than my fetch frequency, the subsequent fetch should retrieve newer data before the socket queue is empty. Is that correct? Am I missing something? Thanks!

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• Nervous about the "real" world

  - by Randy

  I am currently majoring in Computer Science and minoring in mathematics (the minor is embedded in the major). The program has a strong C++ curriculum. We have done some UNIX and assembly language (not fun) and there is C and Java on the way in future classes that I must take. The program I am in did not use the STL, but rather a STL-ish design that was created from the ground up for the program. From what I have read on, the STL and what I have taken are very similar but what I used seemed more user friendly. Some of the programs that I had to write in C++ for assignments include: a password server that utilized hashing of the passwords for security purposes, a router simulator that used a hash table and maps, a maze solver that used depth first search, a tree traveler program that traversed a tree using levelorder, postorder, inorder, selection sort, insertion sort, bit sort, radix sort, merge sort, heap sort, quick sort, topological sort, stacks, queues, priority queues, and my least favorite, red-black trees. All of this was done in three semesters which was just enough time to code them up and turn them in. That being said, if I was told to use a stack to convert an equation to infix notation or something, I would be lost for a few hours. My main concern in writing this is when I graduate and land an interview, what are some of the questions posed to assess my skills? What are some of the most important areas of computer science that are prevalent in the field? I am currently trying to get some ideas of programs I can write in C++ that interest and challenge me to keep learning the language. A sodoku solver came to mind but am lost as to where to start. I apologize for the rant, but I'm just a wee bit nervous about the future. Any tips are appreciated.

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• Real world pitfalls of introducing F# into a large codebase and engineering team

  - by nganju

  I'm CTO of a software firm with a large existing codebase (all C#) and a sizable engineering team. I can see how certain parts of the code would be far easier to write in F#, resulting in faster development time, fewer bugs, easier parallel implementations, etc., basically overall productivity gains for my team. However, I can also see several productivity pitfalls of introducing F#, namely: 1) Everyone has to learn F#, and it's not as trivial as switching from, say, Java to C#. Team members that have not learned F# will be unable to work on F# parts of the codebase. 2) The pool of hireable F# programmers, as of now (Dec 2010) is non-existent. Search various software engineer resume databases for "F#", way less than 1% of resumes contain the keyword. 3) Community support as of now (Dec 2010) is less available. You can google almost any problem in C# and find someone that has already dealt with it, not so with F#. Third party tool support (NUnit, Resharper etc) is also sketchy. I realize that this is a bit Catch-22, i.e. if people like me don't use F# then the community and tools will never materialize, etc. But, I've got a company to run, and I can be cutting edge but not bleeding edge. Any other pitfalls I'm not considering? Or anyone care to rebut the pitfalls I've mentioned? I think this is an important discussion and would love to hear your counter-arguments in this public forum that may do a lot to increase F# adoption by industry. Thanks.

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• How should I log time spent on multiple tasks?

  - by xenoterracide

  In Joel's blog on evidence based scheduling he suggests making estimates based on the smallest unit of work and logging extra work back to the original task. The problem I'm now experiencing is that I'll have create object A with subtask method A which creates object B and test all of the above. I create tasks for each of these that seems to be resulting in ok-ish estimates (need practice), but when I go to log work I find that I worked on 4 tasks at once because I tweak method A and find a bug in the test and refactor object B all while coding it. How should I go about logging this work? should I say I spent, for example, 2 hours on each of the 4 tasks I worked on in the 8 hour day?

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• Help to calculate hours and minutes between two time periods in Excel 2007

  - by Mestika

  Hi, I’m working on a very simple timesheet for my work in Excel 2007 but have ran into trouble about calculate the hours and minutes between two time periods. I have a field: timestart which could be for example: 08:30 Then I have a field timestop which could be for example: 12:30 I can easy calculate the result myself which is 4 hours but how do I create a “total” table all the way down the cell that calculate the hours spend on each entry? I’ve tried to play around with the time settings but it just give me wrong numbers each time. Sincerely Mestika

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• Time tracking tool for monitoring application usage

  - by wizlog

  I want to know how I'm really using my computer, and where the time goes (eg. I have an English paper due, and I intend on getting it done, its 2:30 PM... no wait, its 8:30 PM...). What software can tell me- a. what programs I use, and when b. within programs like Google Chrome or Firefox, which tabs do I spend the most time on. (So I know if I'm spending the time playing a game, or watching a movie on Hulu...)

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• How to change time (Advanced Eastern Time) on Slackware 8.1

  - by r0ca

  Hi all, I have a linux (Slackware) machine and the time/date is like, June 23rd 2003, 10:00am (It's 11 here) and I am not able to set the time to have it correct. I change the timezome to Montreal but the time is still wrong. Is there a way to force it to sync with my domain controler or even another online NTP server? Thanks, David.

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• Amazon EC2 instances changes server time/date on reboots and other time weirdness

  - by puffpio

  I have a windows instance up in EC2. I manually set the timezone to Pacific. 1) For some reason using window's built in time sync doesn't work in the instance...but whatever. I turn off automatic time syncing... but 2) On reboot the time on the server changes! For example, if i reboot it at 4PM on Wednesday, when the server comes back up it will read 12 noon on Thursday! As a result any access to Amazon's other services like SImpleDB fail because the timestamps generated are too far off the current time. Has anyone seen this or figured this out?

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• Time Warp

  - by Jesse

  It’s no secret that daylight savings time can wreak havoc on systems that rely heavily on dates. The system I work on is centered around recording dates and times, so naturally my co-workers and I have seen our fair share of date-related bugs. From time to time, however, we come across something that we haven’t seen before. A few weeks ago the following error message started showing up in our logs: “The supplied DateTime represents an invalid time. For example, when the clock is adjusted forward, any time in the period that is skipped is invalid.” This seemed very cryptic, especially since it was coming from areas of our application that are typically only concerned with capturing date-only (no explicit time component) from the user, like reports that take a “start date” and “end date” parameter. For these types of parameters we just leave off the time component when capturing the date values, so midnight is used as a “placeholder” time. How is midnight an “invalid time”? Globalization Is Hard Over the last couple of years our software has been rolled out to users in several countries outside of the United States, including Brazil. Brazil begins and ends daylight savings time at midnight on pre-determined days of the year. On October 16, 2011 at midnight many areas in Brazil began observing daylight savings time at which time their clocks were set forward one hour. This means that at the instant it became midnight on October 16, it actually became 1:00 AM, so any time between 12:00 AM and 12:59:59 AM never actually happened. Because we store all date values in the database in UTC, always adjust any “local” dates provided by a user to UTC before using them as filters in a query. The error we saw was thrown by .NET when trying to convert the Brazilian local time of 2011-10-16 12:00 AM to UTC since that local time never actually existed. We hadn’t experienced this same issue with any of our US customers because the daylight savings time changes in the US occur at 2:00 AM which doesn’t conflict with our “placeholder” time of midnight. Detecting Invalid Times In .NET you might use code similar to the following for converting a local time to UTC: var localDate = new DateTime(2011, 10, 16); //2011-10-16 @ midnight const string timeZoneId = "E. South America Standard Time"; //Windows system timezone Id for "Brasilia" timezone. var localTimeZone = TimeZoneInfo.FindSystemTimeZoneById(timeZoneId); var convertedDate = TimeZoneInfo.ConvertTimeToUtc(localDate, localTimeZone); The code above throws the “invalid time” exception referenced above. We could try to detect whether or not the local time is invalid with something like this: var localDate = new DateTime(2011, 10, 16); //2011-10-16 @ midnight const string timeZoneId = "E. South America Standard Time"; //Windows system timezone Id for "Brasilia" timezone. var localTimeZone = TimeZoneInfo.FindSystemTimeZoneById(timeZoneId); if (localTimeZone.IsInvalidTime(localDate)) localDate = localDate.AddHours(1); var convertedDate = TimeZoneInfo.ConvertTimeToUtc(localDate, localTimeZone); This code works in this particular scenario, but it hardly seems robust. It also does nothing to address the issue that can arise when dealing with the ambiguous times that fall around the end of daylight savings. When we roll the clocks back an hour they record the same hour on the same day twice in a row. To continue on with our Brazil example, on February 19, 2012 at 12:00 AM, it will immediately become February 18, 2012 at 11:00 PM all over again. In this scenario, how should we interpret February 18, 2011 11:30 PM? Enter Noda Time I heard about Noda Time, the .NET port of the Java library Joda Time, a little while back and filed it away in the back of my mind under the “sounds-like-it-might-be-useful-someday” category.  Let’s see how we might deal with the issue of invalid and ambiguous local times using Noda Time (note that as of this writing the samples below will only work using the latest code available from the Noda Time repo on Google Code. The NuGet package version 0.1.0 published 2011-08-19 will incorrectly report unambiguous times as being ambiguous) : var localDateTime = new LocalDateTime(2011, 10, 16, 0, 0); const string timeZoneId = "Brazil/East"; var timezone = DateTimeZone.ForId(timeZoneId); var localDateTimeMaping = timezone.MapLocalDateTime(localDateTime); ZonedDateTime unambiguousLocalDateTime; switch (localDateTimeMaping.Type) { case ZoneLocalMapping.ResultType.Unambiguous: unambiguousLocalDateTime = localDateTimeMaping.UnambiguousMapping; break; case ZoneLocalMapping.ResultType.Ambiguous: unambiguousLocalDateTime = localDateTimeMaping.EarlierMapping; break; case ZoneLocalMapping.ResultType.Skipped: unambiguousLocalDateTime = new ZonedDateTime( localDateTimeMaping.ZoneIntervalAfterTransition.Start, timezone); break; default: throw new InvalidOperationException(string.Format("Unexpected mapping result type: {0}", localDateTimeMaping.Type)); } var convertedDateTime = unambiguousLocalDateTime.ToInstant().ToDateTimeUtc(); Let’s break this sample down: I’m using the Noda Time ‘LocalDateTime’ object to represent the local date and time. I’ve provided the year, month, day, hour, and minute (zeros for the hour and minute here represent midnight). You can think of a ‘LocalDateTime’ as an “invalidated” date and time; there is no information available about the time zone that this date and time belong to, so Noda Time can’t make any guarantees about its ambiguity. The ‘timeZoneId’ in this sample is different than the ones above. In order to use the .NET TimeZoneInfo class we need to provide Windows time zone ids. Noda Time expects an Olson (tz / zoneinfo) time zone identifier and does not currently offer any means of mapping the Windows time zones to their Olson counterparts, though project owner Jon Skeet has said that some sort of mapping will be publicly accessible at some point in the future. I’m making use of the Noda Time ‘DateTimeZone.MapLocalDateTime’ method to disambiguate the original local date time value. This method returns an instance of the Noda Time object ‘ZoneLocalMapping’ containing information about the provided local date time maps to the provided time zone.  The disambiguated local date and time value will be stored in the ‘unambiguousLocalDateTime’ variable as an instance of the Noda Time ‘ZonedDateTime’ object. An instance of this object represents a completely unambiguous point in time and is comprised of a local date and time, a time zone, and an offset from UTC. Instances of ZonedDateTime can only be created from within the Noda Time assembly (the constructor is ‘internal’) to ensure to callers that each instance represents an unambiguous point in time. The value of the ‘unambiguousLocalDateTime’ might vary depending upon the ‘ResultType’ returned by the ‘MapLocalDateTime’ method. There are three possible outcomes: If the provided local date time is unambiguous in the provided time zone I can immediately set the ‘unambiguousLocalDateTime’ variable from the ‘Unambiguous Mapping’ property of the mapping returned by the ‘MapLocalDateTime’ method. If the provided local date time is ambiguous in the provided time zone (i.e. it falls in an hour that was repeated when moving clocks backward from Daylight Savings to Standard Time), I can use the ‘EarlierMapping’ property to get the earlier of the two possible local dates to define the unambiguous local date and time that I need. I could have also opted to use the ‘LaterMapping’ property in this case, or even returned an error and asked the user to specify the proper choice. The important thing to note here is that as the programmer I’ve been forced to deal with what appears to be an ambiguous date and time. If the provided local date time represents a skipped time (i.e. it falls in an hour that was skipped when moving clocks forward from Standard Time to Daylight Savings Time),  I have access to the time intervals that fell immediately before and immediately after the point in time that caused my date to be skipped. In this case I have opted to disambiguate my local date and time by moving it forward to the beginning of the interval immediately following the skipped period. Again, I could opt to use the end of the interval immediately preceding the skipped period, or raise an error depending on the needs of the application. The point of this code is to convert a local date and time to a UTC date and time for use in a SQL Server database, so the final ‘convertedDate’  variable (typed as a plain old .NET DateTime) has its value set from a Noda Time ‘Instant’. An 'Instant’ represents a number of ticks since 1970-01-01 at midnight (Unix epoch) and can easily be converted to a .NET DateTime in the UTC time zone using the ‘ToDateTimeUtc()’ method. This sample is admittedly contrived and could certainly use some refactoring, but I think it captures the general approach needed to take a local date and time and convert it to UTC with Noda Time. At first glance it might seem that Noda Time makes this “simple” code more complicated and verbose because it forces you to explicitly deal with the local date disambiguation, but I feel that the length and complexity of the Noda Time sample is proportionate to the complexity of the problem. Using TimeZoneInfo leaves you susceptible to overlooking ambiguous and skipped times that could result in run-time errors or (even worse) run-time data corruption in the form of a local date and time being adjusted to UTC incorrectly. I should point out that this research is my first look at Noda Time and I know that I’ve only scratched the surface of its full capabilities. I also think it’s safe to say that it’s still beta software for the time being so I’m not rushing out to use it production systems just yet, but I will definitely be tinkering with it more and keeping an eye on it as it progresses.

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• How to save during real-time collaboration

  - by dev.e.loper

  I want multiple users to edit same document. Problem I'm facing is when a new user joins, he might see an outdated document. How do I make sure that new users get most recent changes? Some solutions I thought of: Save on every change. I don't like this solution because it will slow things down on UI and put load on db. When new user joins, trigger save on all other clients. After other clients saved, load document. With this there can be inconsistency still. Any other suggestions would be helpful.

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• Parametrized Strategy Pattern

  - by ott

  I have several Java classes which implement the strategy pattern. Each class has variable number parameters of different types: interface Strategy { public data execute(data); } class StrategyA implements Strategy { public data execute(data); } class StrategyB implements Strategy { public StrategyB(int paramA, int paramB); public data execute(data); } class StrategyB implements Strategy { public StrategyB(int paramA, String paramB, double paramC); public data execute(data); } Now I want that the user can enter the parameters in some kind of UI. The UI should be chosen at runtime, i.e. the strategies should be independent of it. The parameter dialog should not be monolithic and there should be the possibility to make it behave and look different for each strategy and UI (e.g. console or Swing). How would you solve this problem?

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• Internet Time tab has disappeared from the Date and Time applet of the Control Panel

  - by Robert Thornton

  Previously, there was an Internet Time tab on the Date and Time applet of the Control Panel, wherein one could force a query of an internet time server and also type in a different server from the ones supplied. However, this tab has now disappeared, and I need to have it back. I should mention that this machine has never been part of a domain, since it seems that machines that are such do not have such a tab. I should be obliged to anyone who can help me restore the missing tab. Windows 7 Home Premium Service Pack 1

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