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• Java Cryptography Extension

  - by Adam Tannon

  I was told that in order to support AES256 encryption inside my Java app that I would need the JCE with Unlimited Strength Jurisdiction Policy Files. I downloaded this from Oracle and unzipped it and I'm only seeing 2 JARs: local_policy.jar; and US_export_polic.jar I just want to confirm I'm not missing anything here! My understanding (after reading the README.txt) is that I just drop these two into my <JAVA_HOME>/lib/security/ directory and they should be installed. By the names of these JARs I have to assume that its not the Java Crypto API that cannot handle AES256, but it's in fact a legal issue, perhaps? And that these two JARs basically tell the JRE "yes, it's legally-acceptable to run this level of crypto (AES256)." Am I correct or off-base?

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• Resources for game networking in Java

  - by pudelhund

  I am currently working on a Java multiplayer game. The game itself (single player) already works perfectly fine and so does the chat. The only thing that is really missing is the multiplayer part. Sadly I am absolutely clueless on where to start with that. I roughly know that I will have to work with packages, and I also know many things about streaming etc (chat is already working). Oh and it should - according to this article - be a UDP server. My problem is that I can't find any resources on how to do this. A tutorial (book or website) would be perfect, alternatively a good example of an open source client/server (in Java of course) would be fine as well. If you feel like doing something helpful I'd also really appreciate someone "privately" teaching me via email or some chat program :) Thank you!

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• Can't decide between Java or Python for college [on hold]

  - by Will Harrison

  I'm returning to college in about a month for Computer Science. My problem is, I have been programming on the web since I left (4 years ago), using PHP, ASP.NET, and JavaScript. I want to bone up on a more general purpose language that is cross platform before I begin. I would also like to be using a language that is common at my school and I know that they teach the students C++, Java, and Python. I would like to choose between Java or Python but I'm not sure which one. What do you think would be better based on job prospects in the next 2 years and community?

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• java 2D and swing

  - by user384706

  Hi, I have trouble understanding a fundamental concept in Java 2D. To give a specific example: One can customize a swing component via implementing it's own version of the method paintComponent(Graphics g) Graphics is available to the body of the method. Question: What is exactly this Graphics object, I mean how it is related to the object that has the method paintComponent? Ok, I understand that you can do something like: g.setColor(Color.GRAY); g.fillOval(0, 0, getWidth(), getHeight()); To get a gray oval painted. What I can not understand is how is the Graphics object related to the component and the canvas. How is this drawing actually done? Another example: public class MyComponent extends JComponent { protected void paintComponent(Graphics g) { System.out.println("Width:"+getWidth()+", Height:"+getHeight()); } public static void main(String args[]) { JFrame f = new JFrame("Some frame"); f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); f.setSize(200, 90); MyComponent component = new MyComponent (); f.add(component); f.setVisible(true); } } This prints Width:184, Height:52 What does this size mean? I have not added anything to the frame of size(200,90). Any help on this is highly welcome Thanks

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• Using Java classes in JRuby

  - by kerry

  I needed to do some reflection today so I fired up interactive JRuby (jirb) to inspect a jar.  Surprisingly, I couldn’t remember exactly how to use Java classes in JRuby.  So I did some searching on the internet and found this to be a common question with many answers.  So I figure I will document it here in case I forget how in the future. Add it’s folder to the load path, require it, then use it! $: << '/path/to/my/jars/' require 'myjar' # so we don't have to reference it absolutely every time (optional) include Java::com.goodercode my_object = SomeClass.new

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• Programming in academic environment vs industry environment [closed]

  - by user200340

  Possible Duplicate: Differences between programming in school vs programming in industry? This is a general discussion about programming in the industry environment. The background story is that my colleague sent me a very interesting article called "10 Things Entrepreneurs Don’t Learn in College." The first point in that post is about the author's experience of programming in the academic environment vs industry environment. After finishing a 4 year Computer Science degree course, I am currently working in the academic environment as a developer, mainly writing Java, J2EE, Javascript code. I know there are differences between academic programming and industry programming, but I was shocked after reading that post. Trying to avoid this happening on me in the future, or the others. Can anyone from industry give some general advice about how to program in industry. For example, What exactly happens when a task is received? What is the flow from the beginning to the end? What are the main differences between the programming in industry and academia? Is it more structured? Are more frameworks used? It would be great if some code examples could be given. Thanks.

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• Approaching Java/JVM internals

  - by spinning_plate

  I've programmed in Java for about 8 years and I know the language quite well as a developer, but my goal is to deepen my knowledge of the internals. I've taken undergraduate courses in PL design, but they were very broad academic overviews (in Scheme, IIRC). Can someone suggest a route to start delving into the details? Specifically, are there particular topics (say, garbage collection) that might be more approachable or be a good starting point? Is there a decent high-level book on the internals of the JVM and the design of the Java programming language? My current approach is going to be to start with the JVM spec and research as needed.

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• Java Application for handling records(CRUD)

  - by LivingThing

  I am new to JavaEE and am faced with a tight situation here. I have to develop a Java application for (CRUD) handling records and saving and loading an XML concerning that record. Obviously, I won't be asking you to do this for me. What I would be asking you is to give me some hints/pointer. Initially I thought JAXB would be enough for this but after putting a lot of time learning it and implementing the program I realized that it just can create the XML and read it but for update, delete I would have to do something else. Even if it wasn't for update and delete features requirement for my project I would still think that by just using JAXB is not a good implementation. I was wondering if "REST with Java (JAX-RS) using Jersey" should do the trick for me. ?

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• Immutable Method in Java

  - by Chris Okyen

  In Java, there is the final keyword in lieu of the const keyword in C and C++. In the latter languages there are mutable and immutable methods such as stated in the answer by Johannes Schaub - litb to the question How many and which are the uses of “const” in C++? Use const to tell others methods won't change the logical state of this object. struct SmartPtr { int getCopies() const { return mCopiesMade; } }ptr1; ... int var = ptr.getCopies(); // returns mCopiesMade and is specified that to not modify objects state. How is this performed in Java?

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• DI/IoC in Java for a .NET'er used to Castle.Windsor

  - by Ciddan

  Is there a Java DI container that works in a similar way to the most excellent Castle.Windsor container on the .NET side? The Java containers I've had a look at all seem to rely on annotations (Guice) within my services, which I don't dig all that much - I'd like to go POJO all the way if possible. Spring on the other hand can do without the annotations, but it requires a lot of XML. XML configuration != maintainability. One of the really nice things about Castle.Windsor is the wiring you're able to set up in code with Installers, auto wiring based on naming conventions and whatnot. Ideally the container should also support lifecycle management and configuration; i.e. registering components as transient, singleton, pooled etc. Another bonus would be support for interceptors. Any tips would be greatly appreciated.

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• Java EE 7 JSR Submitted

  - by Tori Wieldt

  Java EE 7 has been filed as JSR 342 in the JCP program. This JSR (Java Specification Request) will develop Java EE 7, the next version of the Java Platform, Enterprise Edition. It is an "umbrella JSR" because the specification includes a collection of several other JSRs. The proposal suggests the addition of two new JSRs: Concurrency Utilities for Java EE (JSR-236) and JCache (JSR-107) as well as updates to JPA, JAX-RS, JSF, Servlets, EJB, JSP, EL, JMS, JAX-WS, CDI, Bean Validation, JSR-330, JSR-250, and Java Connector Architecture. There are also two new APIs under discussion: a Java Web Sockets API and a Java JSON API. These are the new JSRs that are currently up for ballot:• JSR 342: Java Platform, Enterprise Edition 7 Specification• JSR 340: Java Servlet 3.1 Specification• JSR 341: Expression Language 3.0• JSR 343: Java Message Service 2.0• JSR 344: JavaServer Faces 2.2All 5 JSRs are now up for Executive Committee voting with ballots closing on 14 March, and slated for inclusion in Java EE  7.  All of these JSRs are also open for Expert Group nominations. Any JCP member can nominate themself to serve on the Expert Groups for these JSRs. Details on how to become a JCP member are on jcp.org. The JCP gives you a chance to have your own work become an official component of the Java platform and to offer suggestions for improving and growing the technology. Either way, everyone in the Java community benefits from your participation.There's a nice discussion about Java EE 7 in this podcast with Java EE spec lead Robert Chinnici and more information in this blog post on the Aquarium. It's exciting to see so much activity currently underway.

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• Suggestions for connecting .NET WPF GUI with Java SE Server

  - by Sam Goldberg

  BACKGROUND We are building a Java (SE) trading application which will be monitoring market data and sending trade messages based on the market data, and also on user defined configuration parameters. We are planning to provide the user with a thin client, built in .NET (WPF) for managing the parameters, controlling the server behavior, and viewing the current state of the trading. The client doesn't need real-time updates; it will instead update the view once every few seconds (or whatever interval is configured by the user). The client has about 6 different operations it needs to perform with the server, for example: CRUD with configuration parameters query subset of the data receive updates of current positions from server It is possible that most of the different operations (except for receiving data) are just different flavors of managing the configuration parameters, but it's too early in our analysis for us to be sure. To connect the client with the server, we have been considering using: SOAP Web Service RESTful service building a custom TCP/IP based API (text or xml) (least preferred - but we use this approach with other applications we have) As best as I understand, pros and cons of the different web service flavors are: SOAP pro: totally automated in .NET (and Java), modifying server side interface require no code changes in communication layer, just running refresh on Web Service reference to regenerate the classes. con: more overhead in the communication layer sending more text, etc. We're not using J2EE container so maybe doesn't work so well with J2SE REST pro: lighter weight, less data. Has good .NET and Java support. (I don't have any real experience with this, so don't know what other benefits it has.) con: client will not be automatically aware if there are any new operations or properties added (?), so communication layer needs to be updated by developer if server interface changes. con: (both approaches) Server cannot really push updates to the client at regular intervals (?) (However, we won't mind if client polls the server to get updates.) QUESTION What are your opinions on the above options or suggestions for other ways to connect the 2 parts? (Ideally, we don't want to put much work into the communication layer, because it's not the significant part of the application so the more off-the-shelf and automated the better.)

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• Suggestions for connecting .NET WPF GUI with Java SE Server aoo

  - by Sam Goldberg

  BACKGROUND We are building a Java (SE) trading application which will be monitoring market data and sending trade messages based on the market data, and also on user defined configuration parameters. We are planning to provide the user with a thin client, built in .NET (WPF) for managing the parameters, controlling the server behavior, and viewing the current state of the trading. The client doesn't need real-time updates; it will instead update the view once every few seconds (or whatever interval is configured by the user). The client has about 6 different operations it needs to perform with the server, for example: CRUD with configuration parameters query subset of the data receive updates of current positions from server It is possible that most of the different operations (except for receiving data) are just different flavors of managing the configuration parameters, but it's too early in our analysis for us to be sure. To connect the client with the server, we have been considering using: SOAP Web Service RESTful service building a custom TCP/IP based API (text or xml) (least preferred - but we use this approach with other applications we have) As best as I understand, pros and cons of the different web service flavors are: SOAP pro: totally automated in .NET (and Java), modifying server side interface require no code changes in communication layer, just running refresh on Web Service reference to regenerate the classes. con: more overhead in the communication layer sending more text, etc. We're not using J2EE container so maybe doesn't work so well with J2SE REST pro: lighter weight, less data. Has good .NET and Java support. (I don't have any real experience with this, so don't know what other benefits it has.) con: client will not be automatically aware if there are any new operations or properties added (?), so communication layer needs to be updated by developer if server interface changes. con: (both approaches) Server cannot really push updates to the client at regular intervals (?) (However, we won't mind if client polls the server to get updates.) QUESTION What are your opinions on the above options or suggestions for other ways to connect the 2 parts? (Ideally, we don't want to put much work into the communication layer, because it's not the significant part of the application so the more off-the-shelf and automated the better.)

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• Java Dynamic Binding

  - by Chris Okyen

  I am having trouble understanding the OOP Polymorphic principl of Dynamic Binding ( Late Binding ) in Java. I looked for question pertaining to java, and wasn't sure if a overall answer to how dynamic binding works would pertain to Java Dynamic Binding, I wrote this question. Given: class Person { private String name; Person(intitialName) { name = initialName; } // irrelevant methods is here. // Overides Objects method public void writeOutput() { println(name); } } class Student extends Person { private int studentNumber; Student(String intitialName, int initialStudentNumber) { super(intitialName); studentNumber = initialStudentNumber; } // irrellevant methods here... // overides Person, Student and Objects method public void writeOutput() { super.writeOutput(); println(studentNumber); } } class Undergaraduate extends Student { private int level; Undergraduate(String intitialName, int initialStudentNumber,int initialLevel) { super(intitialName,initialStudentNumber); level = initialLevel; } // irrelevant methods is here. // overides Person, Student and Objects method public void writeOutput() { super.writeOutput(); println(level); } } I am wondering. if I had an array called person declared to contain objects of type Person: Person[] people = new Person[2]; person[0] = new Undergraduate("Cotty, Manny",4910,1); person[1] = new Student("DeBanque, Robin", 8812); Given that person[] is declared to be of type Person, you would expect, for example, in the third line where person[0] is initialized to a new Undergraduate object,to only gain the instance variable from Person and Persons Methods since doesn't the assignment to a new Undergraduate to it's ancestor denote the Undergraduate object to access Person - it's Ancestors, methods and isntance variables... Thus ...with the following code I would expect person[0].writeOutput(); // calls Undergraduate::writeOutput() person[1].writeOutput(); // calls Student::writeOutput() person[0] to not have Undergraduate's writeOutput() overidden method, nor have person[1] to have Student's overidden method - writeOutput(). If I had Person mikeJones = new Student("Who?,MikeJones",44,4); mikeJones.writeOutput(); The Person::writeOutput() method would be called. Why is this not so? Does it have to do with something I don't understand about relating to arrays? Does the declaration Person[] people = new Person[2] not bind the method like the previous code would?

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• Kronos Workforce Mobile Apps (w/Java ME tech) lets bosses and staff work better

  - by hinkmond

  The Kronos Workforce Mobile apps let bosses spy on their workers, and let workers do what workers do best (uh, you know, work?), all using Java ME technology. See: Enable your Mobile Workforce w/Kronos Here's a quote: Kronos® Workforce Mobile™ Manager – allows managers to use their devices to monitor workforce operations, resolve exceptions, and respond quickly to employee requests. Kronos Workforce Mobile Employee – enables employees to track their work in real time, quickly and easily review information such as their schedules and timecards, and request time off. Kronos mobile applications are delivered as native applications for [blah-blah-blah]. A JavaME option is also available, which runs on a wide range of feature phones. Good stuff for the enterprise. Java ME technology helps run the mobile enterprise. I like that. Kinda catchy... Hinkmond

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• Immutable Method Java

  - by Chris Okyen

  In Java, there is the final keyword in lieu of the const keyword in c and c++. In the latter languages their is mutable and immutable methods such as stated in one answer by Johannes Schaub - litb the question how-many-and-which-are-the-uses-of-const-in-ce Use const to tell others methods won't change the logical state of this object. struct SmartPtr { int getCopies() const { return mCopiesMade; } }ptr1; ... int var = ptr.getCopies(); // returns mCopiesMade and is specified that to not modify objects state. How is this performed in Java?

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• Are JSP and Java still relevant?

  - by dyyyy

  I've been working so long in java and jsp, that for me it's a no-brainer to use it. But now as I'm starting to do my own framework for web applications, I'm wondering if jsp is the right choice. Seing how much php is popular (as well as other languages as ruby and python) Is JSP still a relevant language. Does it have any clear advantage over other languages ? I don't want to use it just because i know it better. So please considering I know nothing, is there a reason to use JSP and JAVA? Thank you

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• How do I set up ServletForwardingController to intercept for jsp requests on weblogic

  - by dok

  My end goal is to be able to use the spring message tag with configured messageSource on a legacy app using a model-1 architecture. I've done this in tomcat with something like <bean id="messageSource" class="org.springframework.context.support.ReloadableResourceBundleMessageSource"> <property name="basename" value="WEB-INF/classes/bundle"/> </bean> <bean id="urlMapping" class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping"> <property name="mappings"> <props> <prop key="*">myServletForwardingController</prop> </props> </property> </bean> <bean id="myServletForwardingController" name="/**/*.jsp" class="org.springframework.web.servlet.mvc.ServletForwardingController"> <property name="servletName" value="jsp"/> </bean> For weblogic I have <bean id="messageSource" class="org.springframework.context.support.ReloadableResourceBundleMessageSource"> <property name="basenames"> <list> <value>WEB-INF/i18n/bundle</value> </list> </property> </bean> <bean name="/**/*.jsp" class="org.springframework.web.servlet.mvc.ServletForwardingController"> <property name="servletName" value="JspServlet"/> </bean> But, no luck. I'm getting a StackOverflowError when I attempt to access a JSP. java.lang.StackOverflowError at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClass(ClassLoader.java:620) at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:124) at weblogic.utils.classloaders.GenericClassLoader.defineClass(GenericClassLoader.java:338) at weblogic.utils.classloaders.GenericClassLoader.findLocalClass(GenericClassLoader.java:291) at weblogic.utils.classloaders.GenericClassLoader.findClass(GenericClassLoader.java:259) at weblogic.utils.classloaders.ChangeAwareClassLoader.findClass(ChangeAwareClassLoader.java:54) at java.lang.ClassLoader.loadClass(ClassLoader.java:306) at java.lang.ClassLoader.loadClass(ClassLoader.java:251) at weblogic.utils.classloaders.GenericClassLoader.loadClass(GenericClassLoader.java:179) at weblogic.utils.classloaders.ChangeAwareClassLoader.loadClass(ChangeAwareClassLoader.java:35) at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:319) at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClass(ClassLoader.java:620) at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:124) at weblogic.utils.classloaders.GenericClassLoader.defineClass(GenericClassLoader.java:338) at weblogic.utils.classloaders.GenericClassLoader.findLocalClass(GenericClassLoader.java:291) at weblogic.utils.classloaders.GenericClassLoader.findClass(GenericClassLoader.java:259) at weblogic.utils.classloaders.ChangeAwareClassLoader.findClass(ChangeAwareClassLoader.java:54) at java.lang.ClassLoader.loadClass(ClassLoader.java:306) at java.lang.ClassLoader.loadClass(ClassLoader.java:251) at weblogic.utils.classloaders.GenericClassLoader.loadClass(GenericClassLoader.java:179) at weblogic.utils.classloaders.ChangeAwareClassLoader.loadClass(ChangeAwareClassLoader.java:35) at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:319) at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:683) at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:552) at javax.servlet.http.HttpServlet.service(HttpServlet.java:707) at javax.servlet.http.HttpServlet.service(HttpServlet.java:820) at weblogic.servlet.internal.StubSecurityHelper$ServletServiceAction.run(StubSecurityHelper.java:226) at weblogic.servlet.internal.StubSecurityHelper.invokeServlet(StubSecurityHelper.java:124) at weblogic.servlet.internal.ServletStubImpl.execute(ServletStubImpl.java:283) at weblogic.servlet.internal.ServletStubImpl.onAddToMapException(ServletStubImpl.java:394) at weblogic.servlet.internal.ServletStubImpl.execute(ServletStubImpl.java:309) at weblogic.servlet.internal.ServletStubImpl.execute(ServletStubImpl.java:175) at weblogic.servlet.internal.RequestDispatcherImpl.invokeServlet(RequestDispatcherImpl.java:533) at weblogic.servlet.internal.RequestDispatcherImpl.forward(RequestDispatcherImpl.java:266) at org.springframework.web.servlet.mvc.ServletForwardingController.handleRequestInternal(ServletForwardingController.java:129) at org.springframework.web.servlet.mvc.AbstractController.handleRequest(AbstractController.java:153) at org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter.handle(SimpleControllerHandlerAdapter.java:48) at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:771) at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:716) at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:647) at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:552) at javax.servlet.http.HttpServlet.service(HttpServlet.java:707) at javax.servlet.http.HttpServlet.service(HttpServlet.java:820) ...

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• Tech Cast Live - Java and Oracle, One Year Later - February 15th 10AM PST

  - by Cassandra Clark

  Join us for a special live conversation with Ajay Patel, Vice President of Product Development for Application Grid Products and Justin Kestelyn, Director of the Oracle Technology Network. Justin and Ajay will discuss the changes that have come to Java and Oracle since the Sun acquisition, just over a year ago. This live broadcast conversation will include discussion on: - Highlights, challenges and what we learned over the past year - The Future of Java and its importance to Oracle and the community - Oracle's Application Grid product portfolio today Watch Live Event February 15th Watch Archived TechCast Lives You will also have the chance to submit questions to the speakers live on the show, for real-time feedback by using #techcastlive. If your question is read on air we will send you a Free I am the Future of Java t-shirt* *Promotion Details After you have submitted your question and it is read on the live TechCast held February 15th your shirt should arrive in two to four weeks while supplies last. No purchase, payments, or fees are required to receive the gift. Limit one thank you gift per person, and the offer is available only while supplies last. Oracle reserves the right to modify or terminate this offer at any time, for any reason. This offer is not available to Oracle employees or residents of countries subject to U.S. embargo (including Cuba, Iran, Iraq, Libya, North Korea, Sudan, and Syria). Due to Federal Government regulations, this offer is not available to Federal Government customers. Those residing in India or Brazil will be given a substitute gift as we can not ship t-shirts to your country. You are responsible for complying with your employer's policies regarding acceptance of promotional items, and for government laws, regulations and agency policies, if you are a government employee you will not be able to participate. Must be 18 years of age or older. Void where prohibited. Neither Oracle nor any third party assisting Oracle with this offer is responsible for any problems, errors, delays, or technical malfunction related to or impacting this offer. Oracle respects your right to privacy and your information will not be distributed or used for any other purpose. For more information on Oracle's privacy policy, please review our http://www.oracle.com/html/privacy-policy.html. If you have any questions, please contact us at [email protected].

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• Catching multiple exceptions on the client is robust and easy

  - by Alexander Kuznetsov

  Maria Zakourdaev has just demonstrated that if our T-SQL throws multiple exceptions, ERROR_MESSAGE() in TRY..CATCH block will only expose one. When we handle errors in C#, we have a very easy access to all errors. The following procedure throws two exceptions: CREATE PROCEDURE dbo.ThrowsTwoExceptions AS BEGIN ; RAISERROR ( 'Error 1' , 16 , 1 ) ; RAISERROR ( 'Error 2' , 16 , 1 ) ; END ; GO EXEC dbo.ThrowsTwoExceptions ; Both exceptions are shown by SSMS: Msg 50000 , LEVEL 16 , State 1 , PROCEDURE...(read more)

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• which service to use among Amazon's free tier for Java app

  - by vikas devde

  this is the first time I am going to host a java app, Amazon offers a free tier which provides free usage for one year, and I am going to use it. But there are so many services (S3, EC2, etc etc), I cant figure out which service is for web hosting, which service is for what use, their docs is so huge, I am confused, what to read. can anybody write some good points, about which service to use specifically for Java apps, how much I will be charged, and they ask for credit/debit card credential for signup, does it mean they will debit me even in the free period?

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• Designing an API on top with Java RMI and Rest APIs

  - by user1303881

  I'm working on the backend of a java web application. We have a document repository (Fedora Commons specifically) where we house xml files. I want to abstract the API of the repository internally so that we aren't tightly coupled to one product. I'd also like to give the flexibility of connecting to to a repository via Java RMI or REST APIs. I was hoping to get advice or resources on how to implement something like this. My thought it that I'd have some abstract repository class that had methods like getRecord, updateRecord, and deleteRecord. In the constructor I would pass the URI for the repository and the API method and port. This would allow some flexibility in the future so that if the REST api became more practical, but allow the flexibility or using RMI which could (should?) have better performance. Am I over thinking this or am I on the right path?

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• Book (or resource) on Java bytecode

  - by Andrea

  I am looking for some resources on the JVM bytecode. Ideally I would for a short book; something more than a blog post but not a 800 pages tome. If it is relevant, I am a Scala developer, not a Java one, although I know Java just fine. I would like something that allowed me to read JVM bytecode and answer questions such as: Why does the bytecode has to know about high level construct such as classes? Are subtyping relations still visible in bytecode? How does type erasure work exactly? How do Oracle and Dalvik bytecode differ, and what consequences does this have for, say, developing Android apps with Scala? How does the JVM manage the stack, and why exactly this creates issues with tail call elimination? and so on.

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• java generics and the addAll method

  - by neesh

  What is the correct type of argument to the addAll(..) method in Java collections? If I do something like this: Collection<HashMap<String, Object[]>> addAll = new ArrayList<HashMap<String, Object[]>>(); // add some hashmaps to the list.. currentList.addAll(newElements); //currentList is of type: List<? extends Map<String, Object[]>> I understand I need to initialize both variables. However, I get a compilation error (from eclipse): Multiple markers at this line - The method addAll(Collection<? extends capture#1-of ? extends Map<String,Object[]>>) in the type List<capture#1-of ? extends Map<String,Object[]>> is not applicable for the arguments (List<capture#2-of ? extends Map<String,Object[]>>) - The method addAll(Collection<? extends capture#1-of ? extends Map<String,Object[]>>) in the type List<capture#1-of ? extends Map<String,Object[]>> is not applicable for the arguments (Collection<HashMap<String,Object[]>>) what am I doing wrong?

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• Implementation of instance testing in Java, C++, C#

  - by Jake

  For curiosity purposes as well as understanding what they entail in a program, I'm curious as to how instance testing (instanceof/is/using dynamic_cast in c++) works. I've tried to google it (particularly for java) but the only pages that come up are tutorials on how to use the operator. How do the implementations vary across those langauges? How do they treat classes with identical signatures? Also, it's been drilled into my head that using instance testing is a mark of bad design. Why exactly is this? When is that applicable, instanceof should still be used in methods like .equals() and such right? I was also thinking of this in the context of exception handling, again particularly in Java. When you have mutliple catch statements, how does that work? Is that instance testing or is it just resolved during compilation where each thrown exception would go to?

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