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• JBoss Seam project can not be run/deployed

  - by user1494328

  I created sample application in Seam framework (Seam Web Project) and JBoss Server 7.1. When I try run application, console dislays: 23:29:35,419 ERROR [org.jboss.msc.service.fail] (MSC service thread 1-3) MSC00001: Failed to start service jboss.deployment.unit."secoundProject-ds.xml".PARSE: org.jboss.msc.service.StartException in service jboss.deployment.unit."secoundProject-ds.xml".PARSE: Failed to process phase PARSE of deployment "secoundProject-ds.xml" at org.jboss.as.server.deployment.DeploymentUnitPhaseService.start(DeploymentUnitPhaseService.java:119) [jboss-as-server-7.1.1.Final.jar:7.1.1.Final] at org.jboss.msc.service.ServiceControllerImpl$StartTask.startService(ServiceControllerImpl.java:1811) [jboss-msc-1.0.2.GA.jar:1.0.2.GA] at org.jboss.msc.service.ServiceControllerImpl$StartTask.run(ServiceControllerImpl.java:1746) [jboss-msc-1.0.2.GA.jar:1.0.2.GA] at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886) [rt.jar:1.6.0_24] at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908) [rt.jar:1.6.0_24] at java.lang.Thread.run(Thread.java:662) [rt.jar:1.6.0_24] Caused by: org.jboss.as.server.deployment.DeploymentUnitProcessingException: IJ010061: Unexpected element: local-tx-datasource at org.jboss.as.connector.deployers.processors.DsXmlDeploymentParsingProcessor.deploy(DsXmlDeploymentParsingProcessor.java:85) at org.jboss.as.server.deployment.DeploymentUnitPhaseService.start(DeploymentUnitPhaseService.java:113) [jboss-as-server-7.1.1.Final.jar:7.1.1.Final] ... 5 more Caused by: org.jboss.jca.common.metadata.ParserException: IJ010061: Unexpected element: local-tx-datasource at org.jboss.jca.common.metadata.ds.DsParser.parseDataSources(DsParser.java:183) at org.jboss.jca.common.metadata.ds.DsParser.parse(DsParser.java:119) at org.jboss.jca.common.metadata.ds.DsParser.parse(DsParser.java:82) at org.jboss.as.connector.deployers.processors.DsXmlDeploymentParsingProcessor.deploy(DsXmlDeploymentParsingProcessor.java:80) ... 6 more 23:29:35,452 INFO [org.jboss.as.server.deployment] (MSC service thread 1-4) JBAS015877: Stopped deployment secoundProject-ds.xml in 1ms 23:29:35,455 INFO [org.jboss.as.server] (DeploymentScanner-threads - 2) JBAS015863: Replacement of deployment "secoundProject-ds.xml" by deployment "secoundProject-ds.xml" was rolled back with failure message {"JBAS014671: Failed services" => {"jboss.deployment.unit.\"secoundProject-ds.xml\".PARSE" => "org.jboss.msc.service.StartException in service jboss.deployment.unit.\"secoundProject-ds.xml\".PARSE: Failed to process phase PARSE of deployment \"secoundProject-ds.xml\""}} 23:29:35,457 INFO [org.jboss.as.server.deployment] (MSC service thread 1-1) JBAS015876: Starting deployment of "secoundProject-ds.xml" 23:29:35,920 ERROR [org.jboss.msc.service.fail] (MSC service thread 1-1) MSC00001: Failed to start service jboss.deployment.unit."secoundProject-ds.xml".PARSE: org.jboss.msc.service.StartException in service jboss.deployment.unit."secoundProject-ds.xml".PARSE: Failed to process phase PARSE of deployment "secoundProject-ds.xml" at org.jboss.as.server.deployment.DeploymentUnitPhaseService.start(DeploymentUnitPhaseService.java:119) [jboss-as-server-7.1.1.Final.jar:7.1.1.Final] at org.jboss.msc.service.ServiceControllerImpl$StartTask.startService(ServiceControllerImpl.java:1811) [jboss-msc-1.0.2.GA.jar:1.0.2.GA] at org.jboss.msc.service.ServiceControllerImpl$StartTask.run(ServiceControllerImpl.java:1746) [jboss-msc-1.0.2.GA.jar:1.0.2.GA] at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886) [rt.jar:1.6.0_24] at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908) [rt.jar:1.6.0_24] at java.lang.Thread.run(Thread.java:662) [rt.jar:1.6.0_24] Caused by: org.jboss.as.server.deployment.DeploymentUnitProcessingException: IJ010061: Unexpected element: local-tx-datasource at org.jboss.as.connector.deployers.processors.DsXmlDeploymentParsingProcessor.deploy(DsXmlDeploymentParsingProcessor.java:85) at org.jboss.as.server.deployment.DeploymentUnitPhaseService.start(DeploymentUnitPhaseService.java:113) [jboss-as-server-7.1.1.Final.jar:7.1.1.Final] ... 5 more Caused by: org.jboss.jca.common.metadata.ParserException: IJ010061: Unexpected element: local-tx-datasource at org.jboss.jca.common.metadata.ds.DsParser.parseDataSources(DsParser.java:183) at org.jboss.jca.common.metadata.ds.DsParser.parse(DsParser.java:119) at org.jboss.jca.common.metadata.ds.DsParser.parse(DsParser.java:82) at org.jboss.as.connector.deployers.processors.DsXmlDeploymentParsingProcessor.deploy(DsXmlDeploymentParsingProcessor.java:80) ... 6 more 23:29:35,952 INFO [org.jboss.as.controller] (DeploymentScanner-threads - 2) JBAS014774: Service status report JBAS014777: Services which failed to start: service jboss.deployment.unit."secoundProject-ds.xml".PARSE: org.jboss.msc.service.StartException in service jboss.deployment.unit."secoundProject-ds.xml".PARSE: Failed to process phase PARSE of deployment "secoundProject-ds.xml" My secoundProject-ds.xml: <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE datasources PUBLIC "-//JBoss//DTD JBOSS JCA Config 1.5//EN" "http://www.jboss.org/j2ee/dtd/jboss-ds_1_5.dtd"> <datasources> <local-tx-datasource> <jndi-name>secoundProjectDatasource</jndi-name> <use-java-context>true</use-java-context> <connection-url>jdbc:mysql://localhost:3306/database</connection-url> <driver-class>com.mysql.jdbc.Driver</driver-class> <user-name>root</user-name> <password></password> </local-tx-datasource> </datasources> When I comment tags errors disappear, but application is disabled in browser (The requested resource (/secoundProject/) is not available.). What should I do to fix this problem?

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• SOCharts: Charts by Tags

  - by abhin4v

  Screenshot I created this small app as a weekend hack. It shows the reputations, upvotes, downvotes and accepted answers for a user against the tags for the answers. About I wanted to know how may upvotes I was away from getting the bronze badge for the clojure tag. But I could not find any straightforward way of doing that. So I wrote this app (in Clojure, of course). The SO API is used for the data and the charts are created using the Google Chart API. The charts are opened in the default browser. License Licensed under EPL 1.0. Download If you have Clojure and Leiningen installed, you can simply get the code from https://gist.github.com/725331, save it as socharts.clj and then run lein repl -e "(load \"socharts\")(refer 'socharts.socharts)(-main)" for launching the Swing UI If you don't have Clojure installed, but have Java then download the standalone jar from http://dl.dropbox.com/u/5247/socharts-1.0.0-standalone.jar and run it as javaw -jar socharts-1.0.0-standalone.jar Once the UI is launched, just type your user id in the input box and press <ENTER>. It will take some time to download the data from the SO API (the progress bar shows the download progress) and then it will open the charts in your default browser. You can also run it as a command line app by running lein repl -e "(load \"socharts\")(refer 'socharts.socharts)(-main <userid>)" or java -jar socharts-1.0.0-standalone.jar <userid> where you replace <userid> with your user id. Be warned that because of a missing feature in the SO API, it will fetch the data for each question you have answered. So the maximum limit is 10000 answers (the SO API call limit). Platform All platforms with Java 1.6. Contact You can reach me at abhinav [at] abhinavsarkar [dot] net. Please report bugs/comments/suggestions as answers to this post. Code Code was written in Clojure with the UI in Swing. It is available at https://gist.github.com/725331. It's a public gist so your can fork it if you like to do some changes.

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• Mismanaged Session Cookie Issue Fixed for EBS in JRE 1.6.0_23

  - by Steven Chan

  At last:  some good news for those of you affected by the mismanaged session cookie issue in E-Business Suite environments.  This issue is resolved by the latest Sun Java Runtime Environment 1.6.0_23 (a.k.a. JRE 6u23, internal version 1.6.0_23-b05).See the 1.6.0_23 Update Release Notes for details about what has changed in this release.  This release is available for download from the usual Sun channels and through the 'Java Automatic Update' mechanism.This JRE release has been certified with both Oracle E-Business Suite Release 11i and 12.  We recommend this release for all E-Business Suite users.

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• Absent Code attribute in method that is not native or abstract

  - by kerry

  I got the following, quite puzzling error today when running a unit test: java.lang.ClassFormatError: Absent Code attribute in method that is not native or abstract in class file javax/servlet/http/Cookie A google search found this post, which explains that it is caused by having an interface in the classpath, and not an actual implementation. In this case it’s the java-ee interface. To fix this I added the jetty servlet api implementation to my pom: jetty javax.servlet test Piece of cake. I have run in to this before, so I figured I would capture the fix here in case I run in to it again.

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• How to Upgrade Oracle JDK and remove old JDK settings

  - by obysr

  i searched and not found how to upgrade oracle jdk in here. I'm not satisfied with OpenJDK7 because it doesn't come with Java Compiler. I has installed and configured Sun Java SDK 6 and i want to upgrade to Oracle JDK 7. I searched ppas from launchpad an wubp8 but it didn't work. How should I do to upgrade Sun JDK 6 to Oracle JDK 7 and also clearly remove all Sun JDK 6 settings? I'm very grateful for your answers. Sorry for my english

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• Java Champion Jorge Vargas on Extreme Programming, Geolocalization, and Latin American Programmers

  - by Janice J. Heiss

  In a new interview, up on otn/java, titled “An Interview with Java Champion Jorge Vargas,” Jorge Vargas, a leading Mexican developer, discusses the process of introducing companies to Enterprise JavaBeans through the application of Extreme Programming. Among other things, he gives workshops about building code with agile techniques and creates a master project to build all apps based on Scrum, XP methods and Kanban. He focuses on building core components such as security, login, and menus. Vargas remarks, “This may sound easy, but it’s not—the process takes months and hundreds of hours, but it can be controlled, and with small iterations, we can translate customer requirements and problems of legacy systems to the new system.” In regard to his work with geolocalization, he says: “We have launched a beta program of Yumbling, a geolocalization-based app, with mobile clients for BlackBerry, iPhone, Android, and Nokia, with a Web interface. The first challenge was to design a simple universal mechanism providing information to all clients and to minimize maintenance provision to them. I try not to generalize a lot—to avoid low performance or misunderstanding in processing data. We use the latest Java EE technology—during the last five years, I’ve taught people how to use Java EE efficiently.” Check out the interview here.

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• An Overview of Batch Processing in Java EE 7

  - by Janice J. Heiss

  Up on otn/java is a new article by Oracle senior software engineer Mahesh Kannan, titled “An Overview of Batch Processing in Java EE 7.0,” which explains the new batch processing capabilities provided by JSR 352 in Java EE 7. Kannan explains that “Batch processing is used in many industries for tasks ranging from payroll processing; statement generation; end-of-day jobs such as interest calculation and ETL (extract, load, and transform) in a data warehouse; and many more. Typically, batch processing is bulk-oriented, non-interactive, and long running—and might be data- or computation-intensive. Batch jobs can be run on schedule or initiated on demand. Also, since batch jobs are typically long-running jobs, check-pointing and restarting are common features found in batch jobs.” JSR 352 defines the programming model for batch applications plus a runtime to run and manage batch jobs. The article covers feature highlights, selected APIs, the structure of Job Scheduling Language, and explains some of the key functions of JSR 352 using a simple payroll processing application. The article also describes how developers can run batch applications using GlassFish Server Open Source Edition 4.0. Kannan summarizes the article as follows: “In this article, we saw how to write, package, and run simple batch applications that use chunk-style steps. We also saw how the checkpoint feature of the batch runtime allows for the easy restart of failed batch jobs. Yet, we have barely scratched the surface of JSR 352. With the full set of Java EE components and features at your disposal, including servlets, EJB beans, CDI beans, EJB automatic timers, and so on, feature-rich batch applications can be written fairly easily.” Check out the article here.

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• Is it worth learning either GWT or Vaadin?

  - by NimChimpsky

  I consider myself a decent java/web developer. In my career I have always used servlets and ejb's with a web front end, most recently incoporating jquery and ajax. I can see the theoretical benefit of using GWT or Vaadin: it is my understanding they convert Java code to the required JavaScript/HTML. So the developer gets the benefit of cross browser compatibility and compile time error checking (of web GUI elements). My question is threefold: Are there any other benefits I am missing that would be gained using Vaadin or GWT? I am actually quite confident and productive using HTML and JavaScript - so will I actually see any benefit? Or will it just make my knowledge of these areas redundant (as they are handled by GWT/Vaadin)? Will the end result be that I can create enterprise scale data driven websites in a reasonably short time? I can however already do this, and I have not wasted any time learning GWT/Vaadin.

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• how to concatenate two strings in shell script in 3.13.0-34-generic kernel

  - by saikrishna

  I want to concatenate two strings for the shell file im getting error when i have created the shell file in following manner could you please suggest how to get it set export APP_HOME="/home/sfptladmin/ArchivalDaemon" export JAVA_HOME="/usr/lib/jvm/java-7-oracle/jre" export LIBPATH="/home/sfptladmin/ArchivalDaemon/lib" export CPATH=$APP_HOME/conf export CPATH=$CPATH:$LIBPATH/commons-beanutils-core-1.7.0.jar export CPATH=$CPATH:$LIBPATH/commons-collections-3.2.jar export CPATH=$CPATH:$LIBPATH/commons-io-1.4.jar export CPATH=$CPATH:$LIBPATH/commons-lang.jar export CPATH=$CPATH:$LIBPATH/commons-net.jar export CPATH=$CPATH:$LIBPATH/dataloader-27.0.1-uber.jar export CPATH=$CPATH:$LIBPATH/dom4j-1.6.1.jar export CPATH=$CPATH:$LIBPATH/log4j-1.2.15.jar export CPATH=$CPATH:$LIBPATH/opencsv2.3.jar export CPATH=$CPATH:$LIBPATH/poi-3.7.jar export CPATH=$CPATH:$LIBPATH/poi-ooxml-3.7.jar export CPATH=$CPATH:$LIBPATH/poi-ooxml-schemas-3.7.jar export CPATH=$CPATH:$LIBPATH/wsc-23-min.jar export CPATH=$CPATH:$LIBPATH/xmlbeans-2.5.0.jar export CPATH=$CPATH:$LIBPATH/archival-daemon-main.jar export CPATH=$CPATH:$LIBPATH/sbmclasspath.jar export CPATH=$CPATH java -Xms256m -Xmx512m -classpath $CPATH "-Dfile.encoding=UTF-8" com.genpact.proflow.daemon.archival.manager.ArchivalManager echo $CPATH

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• Why eclipse is hanging while in debug mode ?

  - by Pratik

  We are developing our web application using JAVA GWT framework. We are using Eclipse Indigo as a development GUI. We are facing problems while debugging the JAVA gwt application in eclipse. Most of the time, Eclipse hangs while debugging. We tried to increase the memory buffer size in eclipse but no luck. We had tried to run the eclipse in various environment like Windows, Fedora 16, Cent OS. but some how not getting positive results. Can anyone help me out to decide which OS, and eclipse or version should we have to use so can able to resolve the hanging issue? Thanks in advance. Pratik

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• How could this diagram of the current most lucrative technologies be improved?

  - by Edward Tanguay

  I'm giving a talk in April 2011 on the "Developer English" and showing my non-developer audience, mostly English teachers, various diagrams to explain how developers see their industry etc. One of these diagrams is "Hot Technologies", basically, if you want to become a developer, what technologies should you learn to have the highest chance of (1) getting a job (2) making a good salary, and (3) work with the most exciting technology. This is a draft I made just to get some ideas out, basically C#, PHP, Java are where the bulk of the jobs are. Mobile development has a big future. JavaScript is becoming more and more important, and I want to list "minor technologies" such a Python, Ruby on Rails to the side, I assume e.g. that in general, there are a much smaller percentage of jobs in these technologies as in C#, PHP, Java. How could this diagram be improved?

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• What is the start point in game development? Where to start?

  - by Dragon

  I understand, I'm not unique with such a question, there are a lot of questions like this one. But I hope you'll take a minute and maybe can give me a piece of advice. I have an idea to develop games, but I don't know where is the start point in game development. The learning curve isn't as straight as in learning of a programming language, but I want to give it a try. I have some experience with OOP and programming in general. I know (not too deep) C#, Java programming languages. I searched info on where to start, read a lot of blogs, forums and so on. Once I decided "stop wandering around, just start develop a game" and I started. At the moment I have a console version of very simple game (RPS - rock-paper-scissors) developed with C#. It has different modes: "player vs cpu" and "player vs player". Some time later I looked at the code and decided that it should be refactored or even redeveloped from the scratch. And I thought that time "GUI is what I need. I can add logic later." And now I'm here. I've already decided to make RPS with GUI, then make multiplayer and so on. I'm not thinking about 3D now, 2D is enough. It doesn't matter what language to use: C# or Java, I found frameworks for both - XNA (C#) and Slick (Java). Both are good for 2D game development. But I know nothing about sprites, how to bind objects on the screen and so on. You can say "you don't need it for such simple game like RPS", but RPS is the beginning, I have some ideas like "Tower Defense" game... you know, everybody has ideas, wishes.... and this knowledge is useful and in some way obligatory. So what is the start point to achieve my plans, ideas, wishes? Where to start? Is it possible to make game development learning curve a little bit straight? Or there're ways that amateur and game development beginners use for years? Thank you for you answers and advise in advance. P.S Sorry for that this post turned out an essay, but I tried to express my wish to start acting. Hope I managed to do it.

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• Advice for beginner programmer

  - by user3461957

  I am beginner in software development. I noticed when I try to learn one technology let's say .NET I loose my grip over other for example Java. I thought it would be better to concentrate on one technology either Java or .NET to make significant advancement and be an expert, because they can be many details which one can ignore when keeps on changing between technologies. Is my decision right? Do experts choose this approach? Update: Should I pursue my career knowing one technology or not?

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• javac -cp : cannot find symbol problem [migrated]

  - by LivingThing

  I have 3 classes CustomerAddress, Customer and CustomerMain. Customer has a import statement : import org.abc.customers.CustomerAddress; While CustomerMain has an import statement : import org.abc.customers.CustomerAddress; import org.abc.customers.Customer; The package for all of these classes are package org.abc.customer Now, this program works fine on eclipse but when i try to compile and run on cmd prompt it would not compile javac CustomerAddress.java compiles fine then since Customer depends on CustomerAddress i give javac -cp . Customer.java but the compiler complains error cannot find symbol CustomerAddress Thanks

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• Can one draw a cube using different method/drawing mode?

  - by den-javamaniac

  Hi. I've just started learning gamedev (in particular android EGL based) and have ran over a code from Pro Android Games 2 that looks as follows: /* * Copyright (C) 2007 Google Inc. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package opengl.scenes.cubes; import java.nio.ByteBuffer; import java.nio.ByteOrder; import java.nio.IntBuffer; import javax.microedition.khronos.opengles.GL10; public class Cube { public Cube(){ int one = 0x10000; int vertices[] = { -one, -one, -one, one, -one, -one, one, one, -one, -one, one, -one, -one, -one, one, one, -one, one, one, one, one, -one, one, one, }; int colors[] = { 0, 0, 0, one, one, 0, 0, one, one, one, 0, one, 0, one, 0, one, 0, 0, one, one, one, 0, one, one, one, one, one, one, 0, one, one, one, }; byte indices[] = { 0, 4, 5, 0, 5, 1, 1, 5, 6, 1, 6, 2, 2, 6, 7, 2, 7, 3, 3, 7, 4, 3, 4, 0, 4, 7, 6, 4, 6, 5, 3, 0, 1, 3, 1, 2 }; // Buffers to be passed to gl*Pointer() functions // must be direct, i.e., they must be placed on the // native heap where the garbage collector cannot vbb.asIntBuffer() // move them. // // Buffers with multi-byte datatypes (e.g., short, int, float) // must have their byte order set to native order ByteBuffer vbb = ByteBuffer.allocateDirect(vertices.length*4); vbb.order(ByteOrder.nativeOrder()); mVertexBuffer = vbb.asIntBuffer(); mVertexBuffer.put(vertices); mVertexBuffer.position(0); ByteBuffer cbb = ByteBuffer.allocateDirect(colors.length*4); cbb.order(ByteOrder.nativeOrder()); mColorBuffer = cbb.asIntBuffer(); mColorBuffer.put(colors); mColorBuffer.position(0); mIndexBuffer = ByteBuffer.allocateDirect(indices.length); mIndexBuffer.put(indices); mIndexBuffer.position(0); } public void draw(GL10 gl) { gl.glFrontFace(GL10.GL_CW); gl.glVertexPointer(3, GL10.GL_FIXED, 0, mVertexBuffer); gl.glColorPointer(4, GL10.GL_FIXED, 0, mColorBuffer); gl.glDrawElements(GL10.GL_TRIANGLES, 36, GL10.GL_UNSIGNED_BYTE, mIndexBuffer); } private IntBuffer mVertexBuffer; private IntBuffer mColorBuffer; private ByteBuffer mIndexBuffer;} So it suggests to draw a cube using triangles. My question is: can I draw the same cube using GL_TPOLYGON? If so, isn't that an easier/more understandable way to do things?

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• Is there an algorithm for a pool game?

  - by Dmitri

  Hello! I am looking for algorithm to calculate direction and speed of balls in a pool game. I am sure there has to be some type of open source code for this since pool games are some of the oldest computer games I can remember. I mean, when one ball hits another, I need a algorithm to calculate direction of both of them. It will depend of exact angle of where they hit each other and on speed. I want to practice Java coding, so I am looking for java code or package that has this type of code.

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• Hiring a swing developer - Need some tough assignments

  - by Jay

  I am trying to hire a java swing developer, who would most likely work on a java 1.4 based swing app. I have finalized 2-3 people and I would like to give them a one week assignment on Swing. It has to be a really tough one - something that they can't just copy from the internet and something that tests their in-depth knowledge on Swing. I can think of things like split screen windows, and custom UI controls that would involve custom paining. If you were to prepare such an assignment, what would you do? Please share your thoughts/experiences.

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• Java developer webcasts for customers and partners

  - by Jürgen Kress

    Accelerate Your Development with Oracle WebLogic Suite Many organisations are reducing travel, conference, and training budgets for their developers without any change to the results expected of those developers. So how can you keep up with the latest developments? By receiving training, delivered free of charge, at your desk! Join us during February and March for a series of online events designed and run by the development team at Oracle. Learn how Oracle WebLogic Suite enables a whole new level of productivity for enterprise developers. Virtual Developer Day – 10th February Starting with our Virtual Developer Day on 10th February, join us for a blend of hands-on labs, live chat and presentations covering the latest on WebLogic, Java EE 6 and the programming tenets that have made it a true platform breakthrough. Weekly WebLogic Webcasts from 17th February to 17th March Afterwards, join us every week from 17th February to 17th March for our weekly one-hour webcasts where we will show you how to build an application from the ground up using Java and JEE technologies. Presented by the engineering team for WebLogic, these webcasts will be of great value to developers and architects, not just those already using WebLogic. For registration, full session abstracts and schedule please click here. Don’t miss out! Register now to join our virtual events and keep up with all the latest developments. Find out more and register now For more information on SOA Specialization and the SOA Partner Community please feel free to register at www.oracle.com/goto/emea/soa (OPN account required) Blog Twitter LinkedIn Mix Forum Wiki Website Technorati Tags: WebLogic,Java,Oracle,OTN,OPN,Java EE6,Jürgen Kress

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• Is throwing an error in unpredictable subclass-specific circumstances a violation of LSP?

  - by Motti Strom

  Say, I wanted to create a Java List<String> (see spec) implementation that uses a complex subsystem, such as a database or file system, for its store so that it becomes a simple persistent collection rather than an basic in-memory one. (We're limiting it specifically to a List of Strings for the purposes of discussion, but it could extended to automatically de-/serialise any object, with some help. We can also provide persistent Sets, Maps and so on in this way too.) So here's a skeleton implementation: class DbBackedList implements List<String> { private DbBackedList() {} /** Returns a list, possibly non-empty */ public static getList() { return new DbBackedList(); } public String get(int index) { return Db.getTable().getRow(i).asString(); // may throw DbExceptions! } // add(String), add(int, String), etc. ... } My problem lies with the fact that the underlying DB API may encounter connection errors that are not specified in the List interface that it should throw. My problem is whether this violates Liskov's Substitution Principle (LSP). Bob Martin actually gives an example of a PersistentSet in his paper on LSP that violates LSP. The difference is that his newly-specified Exception there is determined by the inserted value and so is strengthening the precondition. In my case the connection/read error is unpredictable and due to external factors and so is not technically a new precondition, merely an error of circumstance, perhaps like OutOfMemoryError which can occur even when unspecified. In normal circumstances, the new Error/Exception might never be thrown. (The caller could catch if it is aware of the possibility, just as a memory-restricted Java program might specifically catch OOME.) Is this therefore a valid argument for throwing an extra error and can I still claim to be a valid java.util.List (or pick your SDK/language/collection in general) and not in violation of LSP? If this does indeed violate LSP and thus not practically usable, I have provided two less-palatable alternative solutions as answers that you can comment on, see below. Footnote: Use Cases In the simplest case, the goal is to provide a familiar interface for cases when (say) a database is just being used as a persistent list, and allow regular List operations such as search, subList and iteration. Another, more adventurous, use-case is as a slot-in replacement for libraries that work with basic Lists, e.g if we have a third-party task queue that usually works with a plain List: new TaskWorkQueue(new ArrayList<String>()).start() which is susceptible to losing all it's queue in event of a crash, if we just replace this with: new TaskWorkQueue(new DbBackedList()).start() we get a instant persistence and the ability to share the tasks amongst more than one machine. In either case, we could either handle connection/read exceptions that are thrown, perhaps retrying the connection/read first, or allow them to throw and crash the program (e.g. if we can't change the TaskWorkQueue code).

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• what is message passing in OO?

  - by Tom

  I've been studying OO programming, primarily in C++, C# and Java. I thought I had a good grasp on it with my understanding of encapsulation, inheritance and polymorphism (as well as reading a lot of questions on this site). One thing that seems to popup up here and there is the concept of "message passing". Apparently, this is something that is not used whilst OO programming in today's mainstream languages, but is supported by Smalltalk. My questions are: What is message passing? (Can someone give a practical example?) Is there any support for this "message passing" in C++, C# or Java?

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• Is it typical for a provider of a web services to also provide client libraries?

  - by HDave

  My company is building a corporate Java web-app and we are leaning towards using GWT-RPC as the client-server protocol for performance reasons. However, in the future, we will need to provide an API for other enterprise systems to access our data as well. For this, we were thinking of a SOAP based web service. In my experience it is common for commercial providers of enterprise web applications to provide client libraries (Java, .NET, C#, etc.). Is this generally the case? I ask because if so, then why bother using SOAP or REST or any standard web services protocol at all? Why not just create a client libraries that communicate via GWT-RPC?

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• For Programmers familiar with ACM API? Drawing Initials [closed]

  - by user71992

  Possible Duplicate: For Programmers familiar with ACM API? Drawing Initials I came across an exercise (in the book "The Art and Science of Java" by Eric Roberts) that requires using only GArc and GLine classes to create a lettering library which draws your initials on the canvas. This should be made independent of the GLabel class. I'd like to know the correct approach to use in solving this problem. I'm not sure what I have so far is good enough (I'm thinking it's too long). The questions requires that I use a good Top-Down approach. Here's my code so far: //Passes letters to GLetter objects and draws them on the canvas package artScienceJavaExercises.chapter8; import acm.program.*; //import acm.graphics.*; public class DrawInitials extends GraphicsProgram{ public void init(){ resize(400,400); } public void run(){ //String let = readLine("Letter?: "); letter = new GLetter("l"); add(letter, (getWidth()-letter.getWidth()*2)/2, (getHeight()-letter.getHeight())/2); add(new GLetter("o"), (letter.getX()+letter.getWidth()), letter.getY()); } private GLetter letter; } //GLetter Class package artScienceJavaExercises.chapter8; import acm.graphics.*; import java.awt.*; public class GLetter extends GCompound{ private static final int ONE_THIRD = 30; private static final int ROW_2_HEIGHT = 40; private GArc[] arc = new GArc[4]; private GLine[] line = new GLine[24]; public GLetter(String s){ line[0] = new GLine(0,0, ONE_THIRD, 0); line[1] = new GLine(ONE_THIRD,0, ONE_THIRD*2, 0); line[2] = new GLine(ONE_THIRD*2,0, ONE_THIRD*3, 0); line[3] = new GLine(0,0, 0,ONE_THIRD); line[4] = new GLine(ONE_THIRD,0, ONE_THIRD, ONE_THIRD); line[5] = new GLine(ONE_THIRD*2,0, ONE_THIRD*2, ONE_THIRD); line[6] = new GLine(ONE_THIRD*3,0, ONE_THIRD*3, ONE_THIRD); line[7] = new GLine(0,ONE_THIRD, ONE_THIRD*2, ONE_THIRD); line[8] = new GLine(ONE_THIRD,ONE_THIRD, ONE_THIRD*2, ONE_THIRD); line[9] = new GLine(ONE_THIRD*2,ONE_THIRD, ONE_THIRD*3, ONE_THIRD); line[10] = new GLine(0,ONE_THIRD, 0, ONE_THIRD+ROW_2_HEIGHT); line[11] = new GLine(ONE_THIRD, ONE_THIRD, ONE_THIRD, ONE_THIRD+ROW_2_HEIGHT); line[12] = new GLine(ONE_THIRD*2,ONE_THIRD, ONE_THIRD*2, ONE_THIRD+ROW_2_HEIGHT); line[13] = new GLine(ONE_THIRD*3,ONE_THIRD, ONE_THIRD*3, ONE_THIRD+ROW_2_HEIGHT); line[14] = new GLine(0, ONE_THIRD+ROW_2_HEIGHT, ONE_THIRD, ONE_THIRD+ROW_2_HEIGHT); line[15] = new GLine(ONE_THIRD, ONE_THIRD+ROW_2_HEIGHT, ONE_THIRD*2, ONE_THIRD+ROW_2_HEIGHT); line[16] = new GLine(ONE_THIRD*2, ONE_THIRD+ROW_2_HEIGHT, ONE_THIRD*3, ONE_THIRD+ROW_2_HEIGHT); line[17] = new GLine(0, ONE_THIRD+ROW_2_HEIGHT, 0, ONE_THIRD*2+ROW_2_HEIGHT); line[18] = new GLine(ONE_THIRD, ONE_THIRD+ROW_2_HEIGHT, ONE_THIRD, ONE_THIRD*2+ROW_2_HEIGHT); line[19] = new GLine(ONE_THIRD*2, ONE_THIRD+ROW_2_HEIGHT, ONE_THIRD*2, ONE_THIRD*2+ROW_2_HEIGHT); line[20] = new GLine(ONE_THIRD*3, ONE_THIRD+ROW_2_HEIGHT, ONE_THIRD*3, ONE_THIRD*2+ROW_2_HEIGHT); line[21] = new GLine(0,ONE_THIRD*2+ROW_2_HEIGHT, ONE_THIRD, ONE_THIRD*2+ROW_2_HEIGHT); line[22] = new GLine(ONE_THIRD, ONE_THIRD*2+ROW_2_HEIGHT, ONE_THIRD*2, ONE_THIRD*2+ROW_2_HEIGHT); line[23] = new GLine(ONE_THIRD*2,ONE_THIRD*2+ROW_2_HEIGHT, ONE_THIRD*3, ONE_THIRD*2+ROW_2_HEIGHT); for(int i = 0; i<line.length; i++){ add(line[i]); line[i].setColor(Color.BLACK); line[i].setVisible(false); } arc[0] = new GArc(getWidth(), getHeight(), 106.699, 49.341); arc[1] = new GArc(getWidth(), getHeight(), 23.96, 49.341); arc[2] = new GArc(getWidth(), getHeight(), -23.96, -49.341); arc[3] = new GArc(0,0,getWidth(), getHeight(), -106.699, -49.341); for(int i = 0; i<arc.length; i++){ add(arc[i],0,0); arc[i].setColor(Color.BLACK); arc[i].setVisible(false); } paintLetter(s); } private void paintLetter(String s){ if (s.equalsIgnoreCase("l")){ turnOn(line[3]); turnOn(line[10]); turnOn(line[17]); turnOn(line[21]); turnOn(line[22]); turnOn(line[23]); } else if(s.equalsIgnoreCase("o")){ for(int i = 0; i<4; ++i){ turnOn(arc[i]); } turnOn(line[1]); turnOn(line[10]); turnOn(line[13]); turnOn(line[22]); } } private void turnOn(GObject g){ g.setVisible(true); } } I created a class (GLetter.java) with arrays for GArc and GLine objects. They are positioned in certain ways thereby turning certain Glines and/or GArcs on or off (changing visiblity) would create a pattern for a letter. This Gletter uses the if/else statements to determine which pattern to create - this makes me feel my code is too long. There is another class (DrawInitials.java) that simulates a GraphicsProgram and allows the user to pass certain letters as arguments to the GLetter object. I've used 'L' and 'O' as examples. However, I posted this because I'm not sure I'm using the right approach. That's why I need your help. I feel MY CODE IS TOO LONG! The code above is not the complete project...it only draws letters 'L' and 'O' for now.

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• Why is using C++ libraries so complicated?

  - by Pius

  First of all, I want to note I love C++ and I'm one of those people who thinks it is easier to code in C++ than Java. Except for one tiny thing: libraries. In Java you can simply add some jar to the build path and you're done. In C++ you usually have to set multiple paths for the header files and the library itself. In some cases, you even have to use special build flags. I have mainly used Visual Studio, Code Blocks and no IDE at all. All 3 options do not differ much when talking about using external libraries. I wonder why was there made no simpler alternative for this? Like having a special .zip file that has everything you need in one place so the IDE can do all the work for you setting up the build flags. Is there any technical barrier for this?

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• Unable to access jar. Why?

  - by SystemNetworks

  I was making a game in java and exported it as jar file. Then after that, I opeed jar splice. I added the libaries and exported jar. I added the natives then i made a main class. I created a fat jar and put it on my desktop. I'm using Mac OS X 10.8 Mountain Lion. When I put in the terminal, java -jar System Front.jar it says unable to access System Front.jar Even if i double click on the file, it doesen't show up! Help! I'm using slick. I added slick and lwjgl as libraries for the jar splice at the jars.

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• Calling functions from different classes

  - by A Ron Hubbard Clevenger

  I'm writing a program and I'm supposed to check and see if a certain object is in the list before I call it. I set up the contains() method which is supposed to use the equals() method of the Comparable interface I implemented on my Golfer class but it doesn't seem to call it (I put print statements in to check). I can't seem to figure out whats wrong with the code, the ArrayUnsortedList class I'm using to go through the list even uses the correct toString() method I defined in my Golfer class but for some reason it won't use the equals() method I implemented. //From "GolfApp.java" public class GolfApp{ ListInterface <Golfer>golfers = new ArraySortedList<Golfer> (20); Golfer golfer; //..*snip*.. if(this.golfers.contains(new Golfer(name,score))) System.out.println("The list already contains this golfer"); else{ this.golfers.add(this.golfer = new Golfer(name,score)); System.out.println("This golfer is already on the list"); } //From "ArrayUnsortedList.java" protected void find(T target){ location = 0; found = false; while (location < numElements){ if (list[location].equals(target)) //Where I think the problem is { found = true; return; } else location++; } } public boolean contains(T element){ find(element); return found; } //From "Golfer.java" public class Golfer implements Comparable<Golfer>{ //..irrelavant code sniped..// public boolean equals(Golfer golfer) { String thisString = score + ":" + name; String otherString = golfer.getScore() + ":" + golfer.getName() ; System.out.println("Golfer.equals() has bee called"); return thisString.equalsIgnoreCase(otherString); } public String toString() { return (score + ":" + name); } My main problem seems to be getting the find function of the ArrayUnsortedList to call my equals function in the find() part of the List but I'm not exactly sure why, like I said when I have it printed out it works with the toString() method I implemented perfectly. I'm almost positive the problem has to do with the find() function in the ArraySortedList not calling my equals() method. I tried using some other functions that relied on the find() method and got the same results.

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