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  • Does declaring many identical anonymous classes waste memory in java?

    - by depsypher
    I recently ran across the following snippet in an existing codebase I'm working on and added the comment you see there. I know this particular piece of code can be rewritten to be cleaner, but I just wonder if my analysis is correct. Will java create a new class declaration and store it in perm gen space for every call of this method, or will it know to reuse an existing declaration? protected List<Object> extractParams(HibernateObjectColumn column, String stringVal) { // FIXME: could be creating a *lot* of anonymous classes which wastes perm-gen space right? return new ArrayList<Object>() { { add(""); } }; }

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  • How do i setup Login module in my web application? in Java?

    - by Nitesh Panchal
    Hello, I am making web application in java. My username and passwords as well as roles are stored in database. I could use jdbcRealm, but it forces me to use a specific structure which i dont have in my project. So, how do i do it? I am using Glassfish v3.0 with Netbeans 6.8. I read few tutorials about custom LoginModule but i am not getting anything out of it. How do you all people do it practically in your projects? If you can show me code of custom LoginModule then also it will do. Waiting for replies.

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  • How can I Submit client side answers (to a question) to the server using JAVA?

    - by mdrafi
    How can I Submit client side computer user's answers(to a multiple choice question) to the server using JAVA I have a centralized server and about 1000 client systems. In these 1000 systems students take multiple choice quiz at at time (in some 2 hrs time). Now i've to send all these answers of these questions to the server in an asynchronous threaded queue when the student answer each question (all 1000 students) Also client have to wait if the server connection is a failure, in this case students should be able to continue taking quiz/exam. When I get the connection these answers in queue should be submitted to the server system. How can I solve this problem? Please suggest/help me in this.

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  • Java Interfaces Methodology: Should every class implement an interface?

    - by Amir Rachum
    I've been programming in Java for a few courses in the University and I have the following question: Is it methodologically accepted that every class should implement an interface? Is it considered bad practice not to do so? Can you describe a situation where it's not a good idea to use interfaces? Edit: Personally, I like the notion of using Interfaces for everything as a methodology and habit, even if it's not clearly beneficial. Eclipse automatically created a class file with all the methods, so it doesn't waste any time anyway.

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  • Is there an equivalent to C++'s "friend class" in Java?

    - by Ricket
    In C++ there is a concept of a "friend", which has access to a class's private variables and functions. So if you have: class Foo { friend class Bar; private: int x; } then any instance of the class Bar can modify any Foo instance's x member, despite it being private, because Bar is a friend of Foo. Now I have a situation in Java where this functionality would come in handy. There are three classes: Database, Modifier, Viewer. The Database is just a collection of variables (like a struct). Modifier should be "friends" with Database; that is, it should be able to read and write its variables directly. But Viewer should only be able to read Database's variables. How is this best implemented? Is there a good way to enforce Viewer's read-only access of Database?

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  • What in-client caching options work well with Cassandra and Java?

    - by sanity
    I'm currently architecting a system that must be capable of dealing with tens of thousands of writes per second. I am more-or-less settled on using Apache Cassandra for the persistence layer, and will be using Java for the application layer, but there are situations where I need to quickly access data in a way that picks up any changes within seconds. Hitting Cassandra every single time I need to check this data for changes will be too slow, which means I need to use some kind of application layer caching. To ensure that the cached data remains current, ideally it would support some kind of multicast-based cache invalidation. What are my options?

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  • Is the development stack of java/spring/hibernate/eclipse/tomcat/mysql riddled with config hacking?

    - by Blankman
    From a M$ development perspective, using things like vs.net/c#/asp.net/asp.net mvc/sql server, things are pretty much smooth. (Obviously for someone coming from a microsoft background like me). Now I love the idea of open source, linux and terminal servering into the computer and doing things via the command line, no license issues really, etc. I've tried firing up eclipse etc., but I always seem to get stuck on some configuration issue or another. Does it get easier or is it just the territory when you are dealing with the java stack?

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  • Online compilers/runtime for Java, C++, Python and ObjC?

    - by Nocturne
    Does anyone know of a good online compiler/runtime (for C++, Java, Python, ObjC etc.) that I can access on the web? What I'm looking for is something that would allow me to type in a program in a web form and to run the program and see the results online. (Let's not get into the why for now. Suffice it to say for the moment that I don't always have access to a compiler/runtime, and firing up an IDE is just overkill for testing out some code snippets) I know of codepad.org -- but I'm looking for something better.

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  • Java: How do I get the IP of the local interface that can reach a remote IP?

    - by Per Fagrell
    I have a Java application that registers a server component in a service provider, and then sends the service name to a client. The client uses the service name to get an address out of the service provider to the server. However, the server has several interfaces only 1 of which the client get get at, so the service must be registered with the right IP. We discovered the client through a broadcast, so I have the client IP and an Enumeration of the computers network interfaces. How do I match the IP to an interface, not knowing what the netmask of the client IP is? Spontaneously I imagine turning all the addresses to ints and chomping the local ips with their netmask and looking for a 'best match', but I wonder if there is a better way? (this is an enterprise(tm) solution, so cutting out the service provider isn't an option, at least not w/o a political campaign first ;) )

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  • Is it possible to pass arithmetic operators to a method in java?

    - by drJames
    Right now I'm going to have to write a method that looks like this: public String Calculate(String Operator, Double Operand1, Double Operand2) { if (Operator.equals("+")) { return String.valueOf(Operand1 + Operand2); } else if (Operator.equals("-")) { return String.valueOf(Operand1 - Operand2); } else if (Operator.equals("*")) { return String.valueOf(Operand1 * Operand2); } else { return "error..."; } } It would be nice if I could write the code more like this: public String Calculate(String Operator, Double Operand1, Double Operand2) { return String.valueOf(Operand1 Operator Operand2); } So Operator would replace the Arithmetic Operators (+, -, *, /...) Does anyone know if something like this is possible in java?

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  • Java sockets: can I write a TCP server with one thread?

    - by hmp
    From what I read about Java NIO and non-blocking [Server]SocketChannels, it should be possible to write a TCP server that sustains several connections using only one thread - I'd make a Selector that waits for all relevant channels in the server's loop. Is that right, or am I missing some important detail? What problems can I encounter? (Background: The TCP communication would be for a small multiplayer game, so max. 10-20 simultaneous connections. Messages will be sent about every few seconds.)

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  • Create a graph image (png, jpg ..) from an XML file with Java

    - by alibm
    Hello, I have an XML file and I want to create a graph with some entities, then store this graph in an image, JPG or PNG. So is there a library in Java do like this?? Or is there some tricks by parsing XML files and ... ??? Here an example XML file: <?xml version="1.0"?> <process> <p n=1>Tove</p> <p n=2>Jani</p> <p n=2>Bill</p> <p n=4>John</p> </process> And the output will be like this. http://i.imgur.com [slash] YevGX.png Please change [slash] by / to see the image. Thanks in advance. Best Regards, AliBM

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  • How to enforce DB field size limit to related Java String?

    - by Sri Sankaran
    What is the correct way to defend against trying to store more text than can be accommodated in a VARCHAR2 database field? Say the PARTNER_ROLE field of the REGISTRATIONS table is declared as VARCHAR2(80). This field is mapped in the Registration class in Java as public class Registration { @Column(name=”PARTNER_ROLE” length=”80”) private String partnerRole; } However, the setPartnerRole() method allows the user to stuff a string of any length. The problem is encountered only when one subsequently tries to insert or update the REGISTRATIONS record. Oracle complains. What is the correct way to handle this situation?

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  • What web application is recommended when programming in Java for beginners?

    - by user1710260
    I am a beginner (almost no knowledge) to web applications. I have been programming in Java for about a year now. I have being doing some research on the different frameworks that are available and I want to find which one is right for me. From what I found: Play, Stripes, and Spring are good choices for beginners, but how can I compare these frameworks together. What is it that I need to look for when comparing them? My project that I am starting to work on is similar to an App Store. Basically an info site on different apps. Any advise will be appreciated.

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  • Java how does Key Event Handling Mechanism(KeyListeners notified) work ?

    - by Carbonizer
    How does application/JVM know which classes if implemented key handling interfaces ? Does it use java Reflections or does it check all the classes for methods ? How can a application or executing JVM understanding to deliver the user event or call the specific methods on a class that implemented the keylistener interface. Does it look at all the classes if those methods are implemented or how does it know which classes implmented keylistener interface ? If you dont implement the keylistener Interface for a class but still implmentation all its methods. Do the class still process the user event occurred ?

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  • When should one let an application crash because of an exception in Java (design issue)?

    - by JVerstry
    In most cases, it is possible to catch exceptions in Java, even unchecked ones. But, it is not necessarily possible to do something about it (for example out of memory). For other cases, the issue I am trying to solve is a design principle one. I am trying to set-up a design principle or a set of rules indicating when one should give up on an exceptional situation, even if it is detected in time. The objective is trying to not crash the application as much as possible. Has someone already brainstormed and communicated about this? I am looking for specific generic cases and possible solutions, or thumb-rules. UPDATE Suggestions so far: Stop running if data coherency can be compromised Stop running if data can be deleted Stop running if you can't do anything about it (Out of memory...) Stop running if key service is not available or becomes unavailable and cannot be restarted If application must be stopped, degrade as gracefully as possible Use rollbacks in db transactions Log as much relevant information as you can Notify the developers

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  • Does invoking System.gc() in java suggest garbage collection of the tenured generation as well as th

    - by Markus Jevring
    When invoking System.gc() in java (via JMX), it will dutifully (attempt to) clean the young generation. This generally works very well. I have never seen it attempt to clean the tenured generation, though. This leads me to two questions: Can the tenured generation even be collected (i.e. is there actually garbage in this generation, or do all objects in the tenured generation actually still have live references to them)? If the tenured generation can be collected, can this be done via System.gc(), or is there another way to do it (unlikely), or will I simply have to wait until I run out of space in the tenured generation?

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  • On Linux do people chroot a Java Web Application or use IPTables and run as non-root?

    - by Adam Gent
    When you run a Java Servlet Container that you would like to serve both static and dynamic content on port 80 you have the classic question of whether to run the server as: As root in hopefully a chroot jail if you can (haven't gotten this working yet) As a non root user and then use IPTables to forward port 80 to some other port (1024) that the container is running on Both: As a non root user, IPTables, and chroot jail. The problem with opt. 1 is the complexity of chrooting and still the security problems of running root.The problem with opt. 2 is that each Linux distro has a different way of persisting IPTables. Option 3 of course is probably idea but very hard to setup. Finally every distro has the annoying differences in daemon scripts. What do people find as the best distro agnostic solution and are there resources to show how to do this?

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  • Regex to split a string (in Java) so that spaces are preserved?

    - by david
    I need to split a string (in Java) into individual words ... but I need to preserve spaces. An example of the text I need to split is something like this: ABC . . . . DEF . . . . GHI I need to see "ABC", " . . . .", "DEF", ". . . .", and "GHI". Obviously splitting on the space character \s isn't going to work, as all the spaces get swallowed up as one space. Any suggestions? Thanks

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  • Struggling with how to compare hours with different time zones in Java?

    - by Riki
    Hi! I have 2 date object in the database that represent the company's working hours. I only need the hours but since I have to save date. it appears like this: Date companyWorkStartHour; Date companyWorkEndHour; start hours: 12-12-2001-13:00:00 finish hours: 12-12-2001-18:00:00 I have the timezone of the company and of the user. (my server may be in another timezone). TimeZone userTimeZone; TimeZone companyTimeZone; I need to check if the user's current time (considering his timezone) is within the company working hours (considering the company's time zone). How can I do it? I am struggling for over a week with Java calendar and with no success!

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  • Why does Java ArrayList use per-element casting instead of per-array casting?

    - by user1111929
    What happens inside Java's ArrayList<T> (and probably many other classes) is that there is an internal Object[] array = new Object[n];, to which T Objects are written. Whenever an element is read from it, a cast return (T) array[i]; is done. So, a cast on every single read. I wonder why this is done. To me, it seems like they're just doing unnecessary casts. Wouldn't it be more logical and also slightly faster to just create a T[] array = (T[]) new Object[n]; and then just return array[i]; without cast? This is only one cast per array creation, which is usually far less than the number of reads. Why is their method to be preferred? I fail to see why my idea isn't strictly better?

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  • Why do C# and Java require everything to be in a class?

    - by Javier Badia
    It seemed like this question should have been asked before, but searching found nothing. I've always wondered what's the point of making us put every bit of code inside a class or interface. I seem to remember that there were some advantages to requiring a main() function like C, but nothing for classes. Languages like Python are, in a way, even more object oriented than Java since they don't have primitives, but you can put code wherever you want. Is this some sort of "misinterpretation" of OOP? After all, you can write procedural code like you would in C and put it inside a class, but it won't be object oriented.

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  • How to center string output using printf() and variable width? [java]

    - by Khan
    I'm creating an output in Java using printf() to create table headers. One of the columns needs variable width. Basically it should look like this: //two coords Trial Column Heading 1 (20,30)(30,20) //three coords Trial Column Heading 1 (20,40)(50,10)(90,30) I tried to use: int spacing = numCoords * 7; //size of column printf("Trial %*^s", column, "Column Heading"); But I keep getting output errors when I try to use * or ^ in the conversion statement. Does anyone have any idea what the correct formatting string should be?

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  • Is there a way to specify java annotations in antlr grammar files?

    - by Steve B.
    I'm looking for a way to include a few additional strings in output .java files generated from antlr. Is there a comprehensive listing of available directives? For example, given parser output like this: package com.foo.bar; //<-- this can be generated with @header { .... } //antlr generated import org.antlr.runtime.*; ... //<-- is there a way to generate anything here? public class MyParser { //<--- or here? public void f1(){ ... } } Is there a way to generate strings that appear after the import statements (e.g. class-level annotations) or possibly method annotations?

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  • How do I replace "this" in Java with something that works.

    - by Luke Alderton
    I'm looking to get the showGUI() method work, the compiler says "this" is not a static variable and cannot be referenced from a static context, what would I use to replace "this"? I've tried test.main (test being the package it's in). The reason I'm using the static method showGUI() is because I need the method to be called from another static method, as well as the startup() method. Below are my two main classes. public class Main extends SingleFrameApplication { @Override protected void startup() { showGUI(); } @Override protected void configureWindow(java.awt.Window root) { } public static Main getApplication() { return Application.getInstance(Main.class); } public static void main(String[] args) { launch(Main.class, args); } public static void showGUI() { show(new GUI(this)); } } public class GUI extends FrameView { public GUI(SingleFrameApplication app) { super(app); initComponents(); } private void initComponents() { //all the GUI stuff is somehow defined here } }

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