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  • How to void checked exceptions in Java?

    - by deamon
    I consider checked exception for a design mistake in the Java language. They lead to leaky abstractions and a lot of clutter in the code. It seems that they force the programmer to handle exceptions early although they are in most cases better handled lately. So my question is how to avoid checked exception? My idea is to execute the actual code inside an exception translator using lambda expressions. Example: ExceptionConverter.convertToRuntimeException(() => { // do things that could throw checked exceptions here }); If for example a IOException occurs it gets rethrown as an exception with the same name but from a different class hierarchy (based on RuntimeException). This approach would effectivly remove the need to handle or declare checked exceptions. Exceptions could then be handled where and if it makes sense. Another solution would be to declare IOException throws Exception on each method. What do you think which solution is better? Do you know any better approach to avoid (suppress) checked exceptions in Java?

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  • How to start a high school Java/Android development club for 13-17 year olds

    - by PaulHurleyuk
    My wife is a high school maths teacher, and is considering starting a programming club for 13-17 years olds who show an interest. Their interest seems to be around Apps and Android which I have little experience of. The kids would be (presumably) interested in programming, and have a fairly high level of computing knowledge. We would provide them with resources and some knowledge, but hopefully a lot would be self guided. I'm hoping stack overflow'ers can provide some tips or starting points. Specific things I think I'll need are; A development Environment; Currently I'm looking towards Java and Android, developed in Eclipse, probably installed on donated older hardware Some initial direction; There seem to be a plethora or 'start android' tutorials, so some recommendations for good ones are valuable, as are recommended paper books A Target; Some final project they should be shooting for A Route; This is where I'm most stuck, how to lead them through the required Java concepts and learning they would need Some related questions already out there Language+IDE for teaching high school students? Teaching "web design/development" to high-school home-school group. Good sources? How can I bootstrap a software development community at my school?

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  • "sha256sum mismatch jdk-7u3-linux-x64.tar.gz " error when trying to install Oracle Java

    - by Fawkes5
    i recently tried installed java 7 on ubuntu 12.04 and i think i screwed something up I followed the instructions given here. First you need to remove openjdk for this run the following command from your terminal sudo apt-get purge openjdk* Now you can install Java7 by adding the following repository: sudo add-apt-repository ppa:eugenesan/java sudo apt-get update sudo apt-get install oracle-java7-installer Now everytime i install a new program i get the following error: Download done. sha256sum mismatch jdk-7u3-linux-x64.tar.gz Oracle JDK 7 is NOT installed. dpkg: error processing oracle-java7-installer (--configure): subprocess installed post-installation script returned error exit status 1 Setting up python-central (0.6.17ubuntu1) ... Setting up python-eggtrayicon (2.25.3-11) ... Setting up gmail-notify (1.6.1.1-1ubuntu1) ... Processing triggers for python-central ... Errors were encountered while processing: oracle-java7-installer Error in function: However.The program seems to install and work just fine so it doesn't seem to be a problem preventing me from doing anything So then i reinstalled openjdk by going: sudo apt-get install openjdk* But i still get the same error. going: sudo apt-get install oracle-java7-installer gives me the same error. What is going on? Please let me know if this is clear or not and ill try to explain my issue better

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  • Freescale One Box Unboxing (then installing Java SE Embedded technology)

    - by hinkmond
    So, I get a FedEx delivery the other day... "What cool device could be inside this FedEx Overnight Express Large Box?" I was wondering... Could it be a new Linux/ARM target device board, faster than a Raspberry Pi and better than a BeagleBone Black??? Why, yes! Yes, it was a Linux/ARM target device board, faster than anything around! It was a Freescale i.MX6 Sabre Smart Device Board (SDB)! Cool... Quad Core ARM Cortex A9 1GHz with 1GB of RAM. So, cool... I installed the Freescale One Box OpenWRT Linux image onto its SD card and booted it up into Linux. But, wait! One thing was missing... What was it? What could be missing? Why, it had no Java SE Embedded installed on it yet, of course! So, I went to the JDK 7u45 download link. Clicked on "Accept License Agreement", and clicked on "jdk-7u45-linux-arm-vfp-sflt.tar.gz", installed the bad boy, and all was good. Java SE Embedded 7u45 on a Freescale One Box. Nice... Hinkmond

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  • Java - Using Linear Coordinates to Check Against AI [closed]

    - by Oliver Jones
    I'm working on some artificial intelligence, and I want my AI not to run into given coordinates as these are references of a wall/boundary. To begin with, every time my AI hits a wall, it makes a reference to that position (x,y). When it hits the same wall three times, it uses linear check points to 'imagine' there is a wall going through these coordinates. I want to now prevent my AI from going into that wall again. To detect if my coordinates make a straight line, i use: private boolean collinear(double x1, double y1, double x2, double y2, double x3, double y3) { return (y1 - y2) * (x1 - x3) == (y1 - y3) * (x1 - x2); } This returns true is the given points are linear to one another. So my problems are: How do I determine whether my robot is approaching the wall from its current trajectory? Instead of Java 'imagining' theres a line from 1, to 3. But to 'imagine' a line all the way through these linear coordinantes, until infinity (or close). I have a feeling this is going to require some confusing trigonometry? (REPOST: http://stackoverflow.com/questions/13542592/java-using-linear-coordinates-to-check-against-ai)

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  • Halloween: Season for Java Embedded Internet of Spooky Things (IoST) (Part 3)

    - by hinkmond
    So, let's now connect the parts together to make a Java Embedded ghost sensor using a Raspberry Pi. Grab your JFET transistor, LED light, wires, and breadboard and follow the connections on this diagram. The JFET transistor plugs into the breadboard with the flat part facing left. Then, plug in a wire to the same breadboard hole row as the top JFET lead (green in the diagram) and keep it unconnected to act as an antenna. Then, connect a wire (red) from the middle lead of the JFET transistor to Pin 1 on your RPi GPIO header. And, connect another wire (blue) from the lower lead of the JFET transistor to Pin 25 on your RPi GPIO header, then connect another (blue) wire from the lower lead of the JFET transistor to the long end of a common cathode LED, and finally connect the short end of the LED with a wire (black) to Pin 6 (ground) of the RPi GPIO header. That's it. Easy. Now test it. See: Ghost Sensor Testing Here's a video of me testing the Ghost Sensor circuit on my Raspberry Pi. We'll cover the Java SE app needed to record the ghost analytics in the next post. Hinkmond

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  • Maintaining C/C++/Java skills as a web developer

    - by wwwuser
    When I was in college I learned how to program in C, C++, and Java. Currently, I'm a web developer using front end and back end technologies (HTML/CSS/JS, PHP, MYSQL). While the sorting algorithms and OOP concepts that I learned in college can be applied to web development, I'm looking for ways to keep up my knowledge of all languages. I enjoy programming in C-Style (C/C++/Java) languages and front-end/back-end technologies. Unfortunately, there aren't many options to use C-style languages to build websites. However, I would like to keep up my knowledge and skills in the languages I learned in college as I know they will continue to help me with my growth. What resources are available to keep challenging myself in C-style languages that are relevant to web development? Would contract work for C-style languages be beneficial? Are there sites that offer algorithm challenges? Any help is appreciated. I'm also interested in how others that have asked themselves this have solved this problem.

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  • Should I go with Java or Python for my next project, after using PHP for 5 years? [closed]

    - by vim
    I have a full-time PHP job and I've been working with PHP for 5 years. I'm not willing to stay within this technology stack any more. I also worked with Java for 2 year before, so for me it looks more obvious to switch back to Java. However during last 5 years I was thinking about starting my own project, and now I think I have a very good SAAS idea. I'm completely confused what technology should I use for my project. I don't want to do it in PHP, and after reading many articles about rapid prototype development it seems to me that Django is the best option. I will continue to work full time for my current employer because I need to pay my bills and will work on my project in my free time. The concern I have is should I do my project in Java or Python? To be realistic there is always a risk when you are doing your own project/start-up. If I do it in Java in the worst case scenario I believe I will be able to find a full time Java position because I already have some experience in Java + recent experience in my project. With regards to Python it looks like it is not very popular in my area and salaries are much more lower then for Java. On the other hand I have a feeling that if I chose Java it will take me a way longer to finish my project. Guys I'm completely confused and I need your advice. P.S. I have moved to London 2 years ago from another country, local guys are very welcome to share their thoughts about London's job market.

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  • Java or Python? Career/Start-up advice needed [closed]

    - by vim
    I have a full-time PHP job and I've been working with PHP for 5 years. As you can guess after spending 5 years I'm not willing to stay within this technology stack any more. I also worked with Java for 2 year before, so for me it looks more obvious to switch back to Java. However during last 5 years I was thinking about starting my own project, and now I think I have a very good SAAS idea. I'm completely confused what technology should I use for my project. I don't want to do it in PHP, and after reading many articles about rapid prototype development it seems to me that Django/Ruby is the best option. I will continue to work full time for my current employer because I need to pay my bills and will work on my project in my free time. The concern I have is should I do my project in Java or Python? To be realistic there is always a risk when you are doing your own project/start-up. If I do it in Java in the worst case scenario I believe I will be able to find a full time Java position because I already have some experience in Java + recent experience in my project. With regards to Python it looks like it is not very popular in my area and salaries are much more lower then for Java. On the other hand I have a feeling that if I chose Java it will take me a way longer to finish my project. Guys I'm completely confused and I need your advice. P.S. I have moved to London 2 years ago from another country, local guys are very welcome to share their thoughts about London's job market.

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  • Which field of programming is known as the best practice for Java? [closed]

    - by user1276509
    I'm a CS student and I have some programming background such as PHP, JavaScript and Pascal. Since Java is so popular among local companies and Java is known as market skill, I'm going to learn it. But I don't know in which field I can use it. So I wonder, what can I do with Java? I heard that Java is not good for web development, although there is Play! Framework. I know a lot of people who prefer to use Python, Ruby and PHP for web development instead of Java and its Play. I also heard that Java is not good to write destkop applications, although it's cross-platform. Many programmers prefer C# for destkop. So I see there's only one field which I can use Java for it - is Android development. But I'm not interested in mobile application development. So my question is which field of programming is known as the best practice for Java? Thanks in advance.

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  • ?????????????????????????/???????????Java EE??????????????????????????????????JavaOne Tokyo 2012?????|WebLogic Channel|??????

    - by ???02
    ??????·???????????????????·???????????????????/????????????????????????????――?????6?????????????????????WebLogic Server?????????????????????????????????????????????????????????2012?4???????JavaOne Tokyo 2012????????????????????·????????????????Java EE???????????????????????????????(???)?????????????????????????? ?????????????NTT??????????????????????????·???????????????????????2005???????1??????????·?????????2006??????????????????????Java EE??????????????????????????????????????????????????????????????????????????????????????????????????????????? DU ?????? ???????????????? ???????????? ?? ????????????????????????????????31????????????????????????????·???????????????????????????30?????????????20??????????????3?????????????????????????????????????????????2??????????????????????????????????????????????????????????????????????????????????????????? ????????????????????????????????????????????????????????????2??????????????????????:??/???????????????????????????????????2??????????/???????:????????????????????????????????2??~1????????????/???????????????·??????????? ?????????????????????????????2?????????????????????????·????(B2C????????????????)?????????????????????????????????????????????????????????????????????????????/?????????????????????? ?????????????????????????????????????(???)?????????(??/???????)???????????????????????????????????????????????????????????????????????????????????????????????·?????WebLogic Server????????·?????Informix???????????? ?????????????????????????????????????????B2C??????????C2C???????????????????????????C2C????????????????????????????????????????????????????????????????????????????????????????????????????????????·????????????????????????????????1???????????????????????????????????????????????? ????????????????????????????????????????????????????????????????????????????????Java EE????????????????????????????????????????????????????????????????????????????????????????????????????????????? ??????????????????3???????????????????(Inexpensive):????????????????????????????????(Agile):???????????????????????????(Simple):???????????????????????? ??????????2006???5????????????????????????????????????????Java EE?????????????????????????????????Java?????????????(???)???????????·??????????????????????????????????????????????????????????????????????Java???????????????????????????????????WebLogic Server??????????????????????????????????????(???)???????????????????????????????? ????????????????????????????????????????????WebLogic Server?????????????????????????/???????????????????GlassFish????????????GlassFish????Java EE?????????????????????????????????????????WebLogic Server??????????????????Tomcat???????????????(???)?????????????????????????????????? ????????????????????????????WebLogic Server?????????????WebLogic Server?????????????????????????????????????JRockit Mission Control???????????????(???)??????WebLogic Server?GlassFish????? ???????????????????????????????????C2C??????????????????????????????????????2006???????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????? ?????????????????????????????????????????????RDB?????/????·???(KVS)???????NoSQL?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????? ?????????????/??????????API???????????????????????????????????????KVS?????????????????GlassFish?????KVS??????????API?GlassFish??????????????????????????JAX-RS???????????????(REST API)???????????????????????????????????????????????????????????????? ?KVS??????????API?????????????????????????????????????????????????????????????????????????????????????????????????(???)?????????? ????API?????????????????????????????????????????????170?????????? ??????????Ruby on Rails??????????????????????????????(???)?????????????????????????????????????(???)??????????????????????????????????????????????????????????????????????Maven 2??????????????????????????????????????????????????????????????????????????????????????????????? GlassFish??????????????????????????????????????????????????????????????????????????????? ??????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????? ?????????????????????????????????????????????????????????????????????????????????????????/?????????????????????????????????????????????????/????????????????????????????

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  • Problems with HMAC when switching to Java 6

    - by Pablo Fernandez
    We have recently switched to java6 and it's mandatory in the project. One of our apps that used to work is failing, with this stacktrace (relevant part) java.lang.NoClassDefFoundError: Could not initialize class com.apple.crypto.provider.HmacSHA1 sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39) sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27) java.lang.reflect.Constructor.newInstance(Constructor.java:513) java.lang.Class.newInstance0(Class.java:355) java.lang.Class.newInstance(Class.java:308) java.security.Provider$Service.newInstance(Provider.java:1221) javax.crypto.Mac.a(DashoA13*..) javax.crypto.Mac.init(DashoA13*..) Has anyone had this problem before? Thanks a lot

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  • on Google App Engine 500 Error, it should be 200 instead of 500

    - by Faisal Amjad
    requestToken = function() { var getTokenURI = '/gettoken?userid=' + userid; var httpRequest = makeRequest(getTokenURI, true); httpRequest.onreadystatechange = function() { if (httpRequest.readyState == 4) { if (httpRequest.status == 200) { openChannel(httpRequest.responseText); } else { alert('ERROR: AJAX request status = ' + httpRequest.status); } } } }; function makeRequest(url, async) { var httpRequest; if (window.XMLHttpRequest) { httpRequest = new XMLHttpRequest(); } else if (window.ActiveXObject) { // IE try { httpRequest = new ActiveXObject("Msxml2.XMLHTTP"); } catch (e) { try { httpRequest = new ActiveXObject("Microsoft.XMLHTTP"); } catch (e) { } } } if (!httpRequest) { return false; } httpRequest.open('POST', url, async); httpRequest.send(); return httpRequest; } it is running excellent on localhost...but on google app engine it httpRequest.status equals 500 and goes in else statement. WHY? LOG on google app engine: /getFriendList?userid=d 500 253ms 0kb Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.11 (KHTML, like Gecko) Chrome/23.0.1271.97 Safari/537.11 175.110.179.86 - - [17/Dec/2012:08:35:33 -0800] "POST /getFriendList?userid=d HTTP/1.1" 500 0 "http://faisalimmsngr.appspot.com/" "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.11 (KHTML, like Gecko) Chrome/23.0.1271.97 Safari/537.11" "faisalimmsngr.appspot.com" ms=254 cpu_ms=110 instance=00c61b117caf2d11ca57d2a2296ccd0b902b038a W 2012-12-17 08:35:33.272 Failed startup of context com.google.apphosting.utils.jetty.RuntimeAppEngineWebAppContext@10ff62a{/,/base/data/home/apps/s~faisalimmsngr/1.363934467542140431} org.mortbay.util.MultiException[java.lang.UnsupportedClassVersionError: adv/web/mid/exam/FriendServlet : Unsupported major.minor version 51.0, java.lang.UnsupportedClassVersionError: adv/web/mid/exam/MessageServlet : Unsupported major.minor version 51.0, java.lang.UnsupportedClassVersionError: adv/web/mid/exam/TokenServlet : Unsupported major.minor version 51.0] at org.mortbay.jetty.servlet.ServletHandler.initialize(ServletHandler.java:656) at org.mortbay.jetty.servlet.Context.startContext(Context.java:140) at org.mortbay.jetty.webapp.WebAppContext.startContext(WebAppContext.java:1250) at org.mortbay.jetty.handler.ContextHandler.doStart(ContextHandler.java:517) at org.mortbay.jetty.webapp.WebAppContext.doStart(WebAppContext.java:467) at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50) at com.google.apphosting.runtime.jetty.AppVersionHandlerMap.createHandler(AppVersionHandlerMap.java:219) at com.google.apphosting.runtime.jetty.AppVersionHandlerMap.getHandler(AppVersionHandlerMap.java:194) at com.google.apphosting.runtime.jetty.JettyServletEngineAdapter.serviceRequest(JettyServletEngineAdapter.java:134) at com.google.apphosting.runtime.JavaRuntime$RequestRunnable.run(JavaRuntime.java:447) at com.google.tracing.TraceContext$TraceContextRunnable.runInContext(TraceContext.java:454) at com.google.tracing.TraceContext$TraceContextRunnable$1.run(TraceContext.java:461) at com.google.tracing.TraceContext.runInContext(TraceContext.java:703) at com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContextNoUnref(TraceContext.java:338) at com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContext(TraceContext.java:330) at com.google.tracing.TraceContext$TraceContextRunnable.run(TraceContext.java:458) at com.google.apphosting.runtime.ThreadGroupPool$PoolEntry.run(ThreadGroupPool.java:251) at java.lang.Thread.run(Thread.java:679) java.lang.UnsupportedClassVersionError: adv/web/mid/exam/FriendServlet : Unsupported major.minor version 51.0 at com.google.appengine.runtime.Request.process-c04431eac3a1f275(Request.java) at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClass(ClassLoader.java:634) at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142) at java.net.URLClassLoader.defineClass(URLClassLoader.java:277) at sun.reflect.GeneratedMethodAccessor5.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:616) at java.lang.ClassLoader.loadClass(ClassLoader.java:266) at org.mortbay.util.Loader.loadClass(Loader.java:91) at org.mortbay.util.Loader.loadClass(Loader.java:71) at org.mortbay.jetty.servlet.Holder.doStart(Holder.java:73) at org.mortbay.jetty.servlet.ServletHolder.doStart(ServletHolder.java:242) at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50) at org.mortbay.jetty.servlet.ServletHandler.initialize(ServletHandler.java:685) at org.mortbay.jetty.servlet.Context.startContext(Context.java:140) at org.mortbay.jetty.webapp.WebAppContext.startContext(WebAppContext.java:1250) at org.mortbay.jetty.handler.ContextHandler.doStart(ContextHandler.java:517) at org.mortbay.jetty.webapp.WebAppContext.doStart(WebAppContext.java:467) at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50) at com.google.tracing.TraceContext$TraceContextRunnable.runInContext(TraceContext.java:454) at com.google.tracing.TraceContext$TraceContextRunnable$1.run(TraceContext.java:461) at com.google.tracing.TraceContext.runInContext(TraceContext.java:703) at com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContextNoUnref(TraceContext.java:338) at com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContext(TraceContext.java:330) at com.google.tracing.TraceContext$TraceContextRunnable.run(TraceContext.java:458) at java.lang.Thread.run(Thread.java:679)

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  • Copying a java text file into a String.

    - by Deepak Konidena
    Hi, I run into the following errors when i try to store a large file into a string. Exception in thread "main" java.lang.OutOfMemoryError: Java heap space at java.util.Arrays.copyOf(Arrays.java:2882) at java.lang.AbstractStringBuilder.expandCapacity(AbstractStringBuilder.java:100) at java.lang.AbstractStringBuilder.append(AbstractStringBuilder.java:515) at java.lang.StringBuffer.append(StringBuffer.java:306) at rdr2str.ReaderToString.main(ReaderToString.java:52) As is evident, i am running out of heap space. Basically my pgm looks like something like this. FileReader fr = new FileReader(<filepath>); sb = new StringBuffer(); char[] b = new char[BLKSIZ]; while ((n = fr.read(b)) > 0) sb.append(b, 0, n); fileString = sb.toString(); Can someone suggest me why i am running into heap space error? Thanks.

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  • I am not able launch JNLP aaplications using "Java Web Start"?

    - by akjain
    Up until recently, I was able to launch/open JNLP files in Firefox using Java web start. Don't know what happened all of a sudden JNLP files stopped launching, a splash screen appears saying Java Starting... and then nothing happens. Even the Java Console in the browser and javacpl.cpl applet doesn't open. Tried all possibilities: removed all older version and installed the latest JRE (java version "1.6.0_17"), still it doesn't work. Done some googling for this problem, people suggested to start javaws.exe with -viewer option but same behavior (a splash screen appears saying "Java Starting..." and then disappears) The problem is that I don't know any place (logs etc.) to look for to see what is causing the problem. I am using WinXP SP3, and some of the screenshots below shows further info about my system. I can provide any other detail if required but please help me solve this problem. Update: Although this question is bit old, Following solution fixed above issue for me (indeed this was the actual cause)

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  • Java URL("file://") doesn't work on Windows XP

    - by Soumya Simanta
    For some reason the following code doesn't work on Windows XP. new URL("file://" + tempfile.getAbsolutePath()); I'm using Java 1.6. Java(TM) SE Runtime Environment (build 1.6.0_31-b05) Java HotSpot(TM) Client VM (build 20.6-b01, mixed mode, sharing) However, the same code just works fine in OS X (Lion) and Java 1.6 java version "1.6.0_29" Java(TM) SE Runtime Environment (build 1.6.0_29-b11-402-11M3527) Java HotSpot(TM) 64-Bit Server VM (build 20.4-b02-402, mixed mode) Linux (Linux 2.6.32-38-generic #83-Ubuntu x86_64 GNU/Linux) with Java 1.6 java version "1.6.0_26" Java(TM) SE Runtime Environment (build 1.6.0_26-b03) Java HotSpot(TM) 64-Bit Server VM (build 20.1-b02, mixed mode) Based on this the above code should work.

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  • Persistance JDO - How to query a property of a collection with JDOQL?

    - by Sergio del Amo
    I want to build an application where a user identified by an email address can have several application accounts. Each account can have one o more users. I am trying to use the JDO Storage capabilities with Google App Engine Java. Here is my attempt: @PersistenceCapable @Inheritance(strategy = InheritanceStrategy.NEW_TABLE) public class AppAccount { @PrimaryKey @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY) private Long id; @Persistent private String companyName; @Persistent List<Invoices> invoices = new ArrayList<Invoices>(); @Persistent List<AppUser> users = new ArrayList<AppUser>(); // Getter Setters and Other Fields } @PersistenceCapable @EmbeddedOnly public class AppUser { @Persistent private String username; @Persistent private String firstName; @Persistent private String lastName; // Getter Setters and Other Fields } When a user logs in, I want to check how many accounts does he belongs to. If he belongs to more than one he will be presented with a dashboard where he can click which account he wants to load. This is my code to retrieve a list of app accounts where he is registered. public static List<AppAccount> getUserAppAccounts(String username) { PersistenceManager pm = JdoUtil.getPm(); Query q = pm.newQuery(AppAccount.class); q.setFilter("users.username == usernameParam"); q.declareParameters("String usernameParam"); return (List<AppAccount>) q.execute(username); } But I get the next error: SELECT FROM invoices.server.AppAccount WHERE users.username == usernameParam PARAMETERS String usernameParam: Encountered a variable expression that isn't part of a join. Maybe you're referencing a non-existent field of an embedded class. org.datanucleus.store.appengine.FatalNucleusUserException: SELECT FROM com.softamo.pelicamo.invoices.server.AppAccount WHERE users.username == usernameParam PARAMETERS String usernameParam: Encountered a variable expression that isn't part of a join. Maybe you're referencing a non-existent field of an embedded class. at org.datanucleus.store.appengine.query.DatastoreQuery.getJoinClassMetaData(DatastoreQuery.java:1154) at org.datanucleus.store.appengine.query.DatastoreQuery.addLeftPrimaryExpression(DatastoreQuery.java:1066) at org.datanucleus.store.appengine.query.DatastoreQuery.addExpression(DatastoreQuery.java:846) at org.datanucleus.store.appengine.query.DatastoreQuery.addFilters(DatastoreQuery.java:807) at org.datanucleus.store.appengine.query.DatastoreQuery.performExecute(DatastoreQuery.java:226) at org.datanucleus.store.appengine.query.JDOQLQuery.performExecute(JDOQLQuery.java:85) at org.datanucleus.store.query.Query.executeQuery(Query.java:1489) at org.datanucleus.store.query.Query.executeWithArray(Query.java:1371) at org.datanucleus.jdo.JDOQuery.execute(JDOQuery.java:243) at com.softamo.pelicamo.invoices.server.Store.getUserAppAccounts(Store.java:82) at com.softamo.pelicamo.invoices.test.server.StoreTest.testgetUserAppAccounts(StoreTest.java:39) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:44) at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15) at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:41) at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20) at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:28) at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:31) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:76) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50) at org.junit.runners.ParentRunner$3.run(ParentRunner.java:193) at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:52) at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:191) at org.junit.runners.ParentRunner.access$000(ParentRunner.java:42) at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:184) at org.junit.runners.ParentRunner.run(ParentRunner.java:236) at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:46) at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197) Any idea? I am getting JDO persistance totally wrong?

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  • low-cost RAID NAS for home use?

    - by gravyface
    Have a noisy, power-hungry Pentium 4 based Ubuntu server that I want to replace with a nice, low-power mini-ITX/Intel Atom-based machine to do my network services (DHCP, DNS, IPSec, Web/mail, FTP, etc.) and am thinking of a (hopefully) equally-low powered NAS using NFS over GbE with at least 1 TB space and a RAID 5 (preferred) or RAID 0 (likely) configuration for redundancy with a couple of spare disks I can swap in as needed down the road. Would I be better off getting a full sized ATX mobo/case and configuring the RAID internally? I really want to keep power consumption down as much as possible as I leave my home server up 24/7.

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  • low-cost RAID NAS for home use?

    - by gravyface
    Have a noisy, power-hungry Pentium 4 based Ubuntu server that I want to replace with a nice, low-power mini-ITX/Intel Atom-based machine to do my network services (DHCP, DNS, IPSec, Web/mail, FTP, etc.) and am thinking of a (hopefully) equally-low powered NAS using NFS over GbE with at least 1 TB space and a RAID 5 (preferred) or RAID 0 (likely) configuration for redundancy with a couple of spare disks I can swap in as needed down the road. Would I be better off getting a full sized ATX mobo/case and configuring the RAID internally? I really want to keep power consumption down as much as possible as I leave my home server up 24/7.

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  • Home networking - Wireless switch?

    - by gamers2000
    I currently have a Linksys WRT160N that has a couple wireless clients and a few wired clients. We are planning to switch from DSL to cable and unfortunately, there isn't a cable point in a location close to the wired clients (i.e. the new location of the router would be too far from the wired clients to lay Ethernet cables). Thus, I was wondering if there was a wireless switch of some sort in which it would be a standard Ethernet switch that would connect to my wireless network? (This is a home network,of course.)

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  • Host name resolution on a home network

    - by Kris
    Hi, I have several machines (both virtual and physical) in my internal network at home. Currently I have to connect via 1P addresses. The one main machine I connect with to all the other machines is running Windows Vista. Is there a way I can have some sort of DNS capability inside my network as well so I can refer to these machines with a name? I think this would be a common problem in most households (running a few computers) and I think there might be some simple solutions out there. This would be something most routers should support out of the box - but why don't they? Can anyone recommend some of these or an easy way to accomplish this?

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  • Host name resolution on a home network

    - by Kris
    Hi, I have several machines (both virtual and physical) in my internal network at home. Currently I have to connect via 1P addresses. The one main machine I connect with to all the other machines is running Windows Vista. Is there a way I can have some sort of DNS capability inside my network as well so I can refer to these machines with a name? I think this would be a common problem in most households (running a few computers) and I think there might be some simple solutions out there. This would be something most routers should support out of the box - but why don't they? Can anyone recommend some of these or an easy way to accomplish this?

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  • Configuring home wireless network

    - by dvanaria
    I'm new to setting up a home wireless network. I have Comcast tv/internet/phone service (modem included) as well as a wireless router. My question is pretty basic. How can I tell the performance of the following parts of the network? 1. incoming internet speed 2. speed of the modem 3. speed of the wireless router I basically want as fast an internet connection as possible, of course, but I'm not sure where to look for the bottleneck (and so, not sure where I can spend some money to speed things up). Right now I'm getting about 36 Mbps (as it shows in Windows). If I run an online speed test (xfinity has one) it shows Average download speed of 14.91 Mbps and Average upload speed of 5.72 Mbps. Thanks for your help.

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  • How do I increase my home's bandwidth?

    - by Derek
    I just mistakingly posted this on Stack Exchange but don't know how to delete it... Anyway, I was thinking of building a home server to use instead of renting a VPS, because in the long run it would be cheaper. What I'm concerned with is the bandwidth limit of my house. I know when I'm downloading something off the internet, if I download at high speeds the rest of the computers connected to my router will become slower. Is there any way to avoid this? There are other cable outlets in my house, will connecting a modem and router there avoid this problem?

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  • Windows Vista home premium upgrade to Windows 7 ultimate

    - by chugh97
    I have 2 laptops with Vista Home Premium editions. I bought the upgrade license from MS, to upgrade one of my laptops. I have upgraded one of the laptops fine. Now the question is, If I want to upgrade the second laptop but uninstall the windows 7 on the first one, would this be possible. I am only wanting to swap the OS onto the other laptop as the other one is faster. Is this possible? and if so how can it be done?

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