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• How difficult did you find the Java Certification Exam

  - by user22904

  I'm just starting out as a Java programmer and have very minimal experience. I would like to improve my knowledge and study for the Java certification. I realize everyone will have a different answer but for those who have taken the certification and passed it, I'd really appreciate if you could tell me your experiences. Just a couple of lines to let me know if you found it hard, very hard. Also how much time did you spend studying. Sorry that this is not a good question. My native language is not English so it is hard for me to say what I want to ask.

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• Does 64bit Windows 8 have the same 75% memory-usage limitation for applications as Windows 7?

  - by Barleyman

  64bit Windows 7 (and Windows Vista) have a built-in limit of not being able to use the last 25% of RAM. You will get a low memory warning when you get close to the limit. Even if you disable that warning, applications will run out of memory and crash since the OS will refuse to allocate memory from that last 25%. That was fine when Vista was designed, when machines had 1 GB of total memory, but is pretty daft for today's 8 GB machines. Yes, the system will run cache, etc. on that extra 2 GB, but running out of memory when you have "merely" 2 GB left.... NB: this has nothing to do with the page file. If you limit the page file to a sensible size like 2 GB, you will still see this behavior. The system will cram the page file to the last byte while refusing to touch that 1/4th of the RAM. Does Windows 8 change this behavior? Is there now some fixed minimum free RAM requirement, like 512 MB, or is it still 25%? Can you actually adjust the low memory limit? EDIT: Here is another older post here which discusses this same behavior on Windows 7. There is fixed 25% limit in Windows 7 and I'd like to know if it's still in Windows 8. Windows 7 / Page File Disabled / 12 GB RAM / 2+ GB RAM free and "your computer is running low on memory" Edit2: Here is another link discussing the low memory warning and how to disable it. Note he claims the limit for RAM usage is 80%, not 75%. It would seem to be correct as you can in fact allocate 6.4GB of RAM with 8GB machine. Anything above and beyond that goes to the pagefile, though. http://halflight.com.au/2011/04/06/how-to-disable-low-memory-warnings-and-the-advantages-of-removing-the-page-file/ Edit3: a Here's couple of process explorer screenshots that demonstrate how it goes down. Exhibit1: https://dl.dropbox.com/u/42068601/sysinfo.jpg Exhibit2: https://dl.dropbox.com/u/42068601/sysint2.jpg You can see that Windows 7 will use the memory 6.4GB as the very last resort. I have low memory warning switched off here so programs crashed at the last screenshot allocation. With low memory warning turned on, it starts nagging before you can push OS to use that remaining 1.6GB. The question is not "Is it OK windows does not want to allocate last 20% of RAM because X", it's "Does Windows 8 still behave this way". With 16GB this really becomes dumb.

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• How to upload files to server using JSP/Servlet?

  - by Thang Pham

  How can I upload files to server using JSP/Servlet? I tried this: <form action="upload" method="post"> <input type="text" name="description" /> <input type="file" name="file" /> <input type="submit" /> </form> However, I only get the file name, not the file content. When I add enctype="multipart/form-data" to the <form>, then request.getParameter() returns null. During research I stumbled upon Apache Common FileUpload. I tried this: FileItemFactory factory = new DiskFileItemFactory(); ServletFileUpload upload = new ServletFileUpload(factory); List items = upload.parseRequest(request); // This line is where it died. Unfortunately, the servlet threw an exception without a clear message and cause. Here is the stacktrace: SEVERE: Servlet.service() for servlet UploadServlet threw exception javax.servlet.ServletException: Servlet execution threw an exception at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:313) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298) at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:852) at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588) at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489) at java.lang.Thread.run(Thread.java:637)

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• Survey says: Java technology rules

  - by hinkmond

  Eclipse came out with their Open Source Developer Report and Survey for 2012. In it, we see (in the words of the immortal Richard Dawson, RIP) "Surveys Says!": Java computer programming language is on top. See: Java is the top Here's a quote: The Eclipse community was invited to participate in the survey between April 23 and May 15 of this year. Skerrett says the Foundation promoted the survey primarily through social media (Facebook, Twitter) and online forums. Of the 840 people who responded, 732 completed the survey... So, now we know who's on top, we can keep this in mind the next time this question comes up on Family Feud. Hinkmond

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• Java Swing or Java Qt?

  - by Gili

  Can someone with extensive experience with both Qt and Java Swing please discuss whether you would use Swing or Qt under Java, and why? Secondly, what is the business impact of using Qt? Is it reasonably popular or will I have a hard time finding experienced Qt developers? Are there any other business impacts I should be aware of? UPDATE: I am more interested in the technical and business impacts of Swing vs Qt than the license type/fee since in my case the cost is not a concern.

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• Can I find out if the java program was launched using java or javaw

  - by saugata

  This is related to an earlier question by a different user How to detect that code is running inside eclipse IDE I noticed that eclipse always launches programs with javaw rather than java. (This does not imply a program launched with javaw was launched from eclipse). I can find the arguments passed using RuntimeMXBean RuntimemxBean = ManagementFactory.getRuntimeMXBean(); List<String> lst=RuntimemxBean.getInputArguments(); for(int i=0;i<lst.size();i++) System.out.println(lst.get(i)); But this does not tell me whether it was launched using java or javaw. Is there any way to find it out? Another related question is why does eclipse use javaw to launch programs?

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• SUN Java and GPL V2 licence issue for linked applications

  - by user255607

  I have recently noticed that the Sun Java code has been released as GPL V2 code (see Google code repo). Does that mean that all applications written in Java and linked to Sun APIs (beans, and so on) are also in GPL ? If we strictly follow the GPL then this should be the case (Libs should be in LGPL, not GPL if we want to build proprietary software on top of it). Is there another commercial licence which can avoid such an issue ? I cannot believe this is the case. There must be an explanation on this. Regards, Apple92

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• Why Java as a First Language?

  - by dsimcha

  Why is Java so popular as a first language to teach beginners? To me it seems like a terrible choice: It's statically typed. Static typing isn't useful unless you care a lot about either performance or scaling to large projects. It requires tons of boilerplate to get the simplest code up and running. Try explaining "Hello, world" to someone who's never programmed before. It only handles the middle levels of abstraction well and is single-paradigm, thus leaving out a lot of important concepts. You can't program at a very low level (pointers, manual memory management) or a very high level, (metaprogramming, macros) in it. In general, Java's biggest strength (i.e. the reason people use it despite the shortcomings of the language per se) is its libraries and tool support, which is probably the least important attribute for a beginner language. In fact, while useful in the real world these may negatives from a pedagogical perspective as they can discourage learning to write code from scratch.

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• Learning Java with a simple project

  - by phodu_insaan

  As i remember the time when i was learning PHP, it was suggested to build a simple blog or a forum after reading the language fundamentals. I was told/read that this would cover everything that I would need to learn about PHP from a beginners book. This advice was out there in a number of places, and after following and working with PHP it seems quite good advice. Now, i am learning Java and reading the book "Thinking in Java" by Bruce Eckel. I wonder if there is any such set of similar, small projects that I could take up, that would cover all the essentials and most of what is covered in the book.

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• Where is the used memory in Task Manager & Resource Monitor coming from?

  - by Sam Adams

  On a Windows 7, the working set memory usage plus private memory does not add up to the total used memory in Task Manager and Windows 7 Resource Monitor. How do you find out where the used memory is coming from? The cached memory can't be part of it because sometimes the total cache is greater than the total in use. The commit memory plus the working set also doesn't add up to the total in use - but even that shouldn't be significant if it did, since commit is virtual.

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• Reducing memory for worker MPM in Apache

  - by ShyM

  I've moved from the prefork MPM to the worker MPM due to a process limit I was hitting on my VPS. However, memory usage increased after switching over (which is odd since the worker MPM is supposed to have a smaller memory footprint?). Most of them belong to php-cgi processes. Is there something I'm doing wrong? I have around 20 sites on it, each with a different fcgi wrapper script. Could that be a reason?

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• overview/history of resident memory usage

  - by kapet

  I have a fairly complicated program (Python with SWIG'ed C++ code, long running server) that shows a constantly growing resident memory usage. I've been digging with the usual tools for the leak (valgrind, Pythons gc module, etc.) but to no avail so far. I'm a bit afraid that the actual problem is memory fragmentation within Python and/or libc managed memory. Anyway, my question is more specific right now: Is there a tool to visualize resident memory usage and ideally show how it develops over time? I think the raw data is in /proc/$PID/smaps but I was hoping there's some tool that shows me a nice graph of the amounts used by mmap'ed files vs. anonymous mmap'ed memory vs. heap over time so that it's easier to see (literally) what's changing. I couldn't find anything though. Does anybody know of a ready to use tool that graphs memory usage over space and time in an intuitive way?

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• Java on Ubuntu server 12.04?

  - by Sean Dunwoody

  I'm a little confused at the moment. My back story in short, is that I'm trying to set up a Minecraft server on an Ubuntu server I've recently set up, obviously to do this I needed Java, but after googling for a short while I wasn't entirely sure whether it is possible (or legal?) to do so in Ubuntu 12.04 due to licensing type issues - so I installed open JDK instead which appears not to work properly with the Minecraft server software (I half expected this) I'm now considering uninstalling open JDK and instead trying to get proper Java on there instead, my question is, is this possible? Is it Legal? And if so how do I go about doing it? Because I'm finding it very difficult to find any instructions on how to do so for 12.04 . . .

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• I'm a beginner Java programmer but I want to be useful

  - by user105418

  Programming has always interested me, but after learning some of the basics of Java(I'm talking high school level), I don't really know what to do from there. I want to be able to apply what I learned in some way, whether it be a volunteer project or something, but I probably don't know enough programming. Is it possible for a novice Java programmer to be useful in some way whatsoever. I want to do this because I feel like I could learn more about programming by helping people in theirs, but I'm not sure if I'm even able to this though. Does anyone have any suggestions on how I can contribute to other people's project in some way or how to apply it in some way?

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• How to make game menu Java

  - by Deathsbreed

  I've been searching all over for how to make a game menu, but I haven't found anything useful. I have a very simple Pong like game (source-code here), and I want to add a main menu to it. This wouldn't be too much of a problem if I was making a standalone with JFrame instead of an Applet, but I want this to be available on the web (not downloaded). I might have been able to do some of it myself, except for the fact that it would mean having a very heavy main class (in this case the GNP.java file). So I was thinking, is there a way to basically have a Java Applet and have it use a JFrame and how? and if not, what could I do? Thanks!

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• Java Grade Calculator program for class kepp geting the error "Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException." [migrated]

  - by user2880621

  this is my first question I've posted. I've used this site to look at other questions to help with similar problems I've had. After some cursory looking I couldn't find quite the answer I was looking for so I decided to finally succumb and create an account. I am fairly new to java, only a few weeks into my first class. Anyway, my project is to create a program which takes any amount of students and their grades, and then assign them a letter grade. The catch is, however, that it is on a sort of curve and the other grades' letter are dependent on the the highest. Anything equal to or 10 points below the best grade is an a, anything 11-20 points below is a b, and so on. I am to use an array, but I get this error when ran "Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException." I will go ahead and post my code down below. Thanks for any advice you may be able to give. package grade.calculator; import java.util.Scanner; /** * * @author nichol57 */ public class GradeCalculator { /** * @param args the command line arguments */ public static void main(String[] args) { Scanner input = new Scanner(System.in); System.out.println("Enter the number of students"); int number = input.nextInt(); double[]grades = new double [number]; for (int J = number; J >=0; J--) { System.out.println("Enter the students' grades"); grades[J] = input.nextDouble(); } double best = grades[0]; for (int J = 1; J < number; J++) { if (grades[J] >= best){ best = grades[J]; } } for (int J = 0;J < number; J++){ if (grades[J] >= best - 10){ System.out.println("Student " + J + " score is " + grades[J] + " and grade is " + "A"); } else if (grades[J] >= best - 20){ System.out.println("Student " + J + " score is " + grades[J] + " and grade is " + "B"); } else if (grades[J] >= best - 30) { System.out.println("Student " + J + " score is " + grades[J] + " and grade is " + "C"); } else if (grades[J] >= best - 40) { System.out.println("Student " + J + " score is " + grades[J] + " and grade is " + "D"); } else { System.out.println("Student " + J + " score is " + grades[J] + " and grade is " + "F"); } } // end for loop for output }// end main method }

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• Learning Java for electrical engineering [closed]

  - by MohdAziz

  I'm an electrical engineering student ( Power, control & instrumentation). 2 months ago I started learning C, and I found programming something really enjoyable and I'd like to continue learning C and few other programming languages along with my electrical engineering degree. So my university is offering an extensive Java Oracle course for 7 days (like 5-6 hours a day) for a really decent price, do you think as an electrical engineer this would help me in my future career? What are the benefits of learning Java for an electrical engineer of my specialization? Do you think it's a good idea for someone in my case to take such an extensive course? I'm hardworker and I really enjoy these things, so I don't think that would be a problem for me.

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• Hotel key mobile app for your Java ME cell phone

  - by hinkmond

  This is cool. Get this Java ME app to download your hotel key to your mobile phone without having to check in at the front desk. See: Mobile Key Java ME app Here's a quote: The new [app] makes it possible for ALL smartphone operating systems, including [blah-blah-blah], [yadda-yadda-yadda], J2ME, ... and [blah-blah-blah], to run the Mobile Key App. Mobile Key by OpenWays is the first and only ubiquitous mobile phone- based front-desk bypass solution that is truly deployable today... Nice. Just don't accidentally drop your cell phone in the toilet. You'll be sleeping in the restroom if you do. Just sayin'. Hinkmond

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• Minecraft not working on Ubuntu 11.10, Java 7

  - by user71007

  I got into Minecraft 2 months ago and just today I switched to Ubuntu. I downloaded Java from the special script (http://www.duinsoft.nl/packages.php?t=en) and after I verified it said it was installed. So I downloaded the Minecraft.jar file and ran it through the Java runtime. It updated like the launcher should... ... And it froze. Went black, didn't even get to the Mojang screen. Please help me! Minecraft is my favorite game and I can't stand to lose it.

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• Layering Design Pattern in Java clean code style

  - by zeraDev

  As a Java developer, I am developing trying to use the clean code rules. But in my team we are facing a concrete problem: We have a business layer offering a service called "createObject", this service makes a lot of operation which can result to problem. E.g: parentObjectDontExist, objectAlreadyExist, dontHaveAuthorizationToCreate, operationFailed... and we want the UI using this service to display different information messages depending which error occurred. In old java dev, we should have create all signed exception type and throw it in createObject. As Clean code says, it is forbidden to use Exception for business logic AND signed exceptions are evil... Why not...But i don't know how to solved this problem and i don't want to use return code. How do you do? Thanks for youre experience return.

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• How to structure my java packages

  - by MightyPork

  I have a Java library, quite a huge one. I'm asking regarding Best Practices of structuring the source. For example, the logging sybsystem: Option 1: All in one package, named to sort nicely Log - static accessor LogMonitor - interface for log minotor LogMonitorBase - abstract class LogMonitorStdout - print log to console LogWriter - interface for file logger LogWriterSimple - log writer with just one log file LogWriterArchiving - log writer that handles old log files Option 2: Subpackages for Monitors and Writers, with better names Log monitors/LogMonitor monitors/BaseMonitor monitors/StdoutMonitor writers/LogWriter writers/SimpleLog writers/ArchivingLog The second maybe looks better, but perhaps it's not so practical from the java point of view (two extra packages). What do you suggest as the best practice here? A lot in one package, grouped by naming prefixes, or a lot of subpackages with better names?

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• How to get available memory C++/g++ ?

  - by Agito

  I want to allocate my buffers according to memory available. Such that, when I do processing and memory usage goes up, but still remains in available memory limits. Is there a way to get available memory (I don't know will virtual or physical memory status will make any difference ?). And method has to be platform Independent as its going to be used on Windows, OS X, Linux and AIX. (And if possible then I would also like to allocate some of available memory for my application, someone it doesn't change during the execution).

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• New to Maven-- Creating Java EE Projects

  - by M.C.

  Greetings-- I've been developing Java EE web apps with Eclipse for about a year. My employer doesn't use Maven, but the more I read about it, the more convinced I am that Maven + Hudson will be greatly beneficial for us. First, though, I have to become comfortable with those technologies in my spare time, so that I can create a proof-of-concept. Right now, I'm still a Maven newbie. Is there a set of best practices for creating Java EE web apps with Maven? For example, I could create a project with a basic archetype and then add all of the necessary JARs by putting dependencies in the POM for the servlet container, EJB, EclipseLink, etc... That might work, but it might not be the best way to do it. I'd greatly appreciate any guidance that you could provide on this topic. Thank you very much!

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• Virtual Memory and SSD

  - by Zombian

  While studying for the A+ Exam I was reading about SSD's and I thought to myself that if you had a mobo with a low RAM limit you could use a dedicated SSD purely for Virtual RAM. I looked up some info on line and the info I found said that this was a poor practice but didn't explain why. Why shouldn't SSD's be used for Virtual Memory and what are your thoughts on a dedicated Virtual Memory drive? Thank you!

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• Halloween: Season for Java Embedded Internet of Spooky Things (IoST) (Part 2)

  - by hinkmond

  To start out our ghost hunting here at the Oracle Santa Clara campus office, we first need a ghost sensor. It's pretty easy to build one, since all we need to do is to create a circuit that can detect small fluctuations in the electromagnetic field, just like the fluctuations that ghosts cause when they pass by... Naturally, right? So, we build a static charge sensor and will use a Java Embedded app to monitor for changes in the sensor value, running analytics using Java technology on a Raspberry Pi. Bob's your uncle, and there you have it: a ghost sensor. See: Ghost Detector So, go out to Radio Shack and buy up these items: shopping list: 1 - NTE312 JFET N-channel transistor (this is in place of the MPF-102) 1 - Set of Jumper Wires 1 - LED 1 - 300 ohm resistor 1 - set of header pins Then, grab a flashlight, your Raspberry Pi, and come back here for more instructions... Don't be afraid... Yet. Hinkmond

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