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  • Rails: creating a model in the new action

    - by Joseph Silvashy
    I have an interesting situation, well it's probably not that unique at all, but I'm not totally sure how to tackle it. I have a model, in this case a recipe and the user navigates to the new path /recipes/new however the situation is that I need to be able to have the user upload images and make associations to that model in the new action, but the model doesn't have an ID yet. So I assume I need to rethink my controller, but I don't want to have redirects and whatnot, how can accomplish this? Here is the basic controller, barebones obviously: ... def new # I should be creating the model first, so it has an ID @recipe = Recipe.new end def create @recipe = Recipe.new(params[:recipe]) if @recipe.save redirect_to @recipe else render 'new' end end ... update Perhaps I can have a column thats like state which could have values like new/incomplete/complete or what-have-you. I'm mostly trying to figure out what would also be most efficient for the DB. It would be nice if I could still have a url that said '/new', instead of it be the edit path with the id, for usability sake, but I'm not sure this can be simply accomplished in the new action of my controller. Thoughts?

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  • How do you force a Linux process (Java webstart App) to stop locking a Filesystem (CD-ROM) WITHOUT k

    - by Blake
    In Linux (CentOS 5.4), how do you force a process to stop locking a file system without killing the process? I am trying to get my Java Webstart Application, running locally, to eject a CD. I do not have this problem if I am just browsing through the files using a JFileChooser, but once I read the contents of a file, I can no longer eject the CD...even after removing ALL references to any files. Hitting the eject button will give the error (Title - "Cannot Eject Volume"): "An application is preventing the volume 'volume name' from being ejected" Thus, my goal is to tell the process to stop targeting the CD-ROM in order to free it up. Thank you for any help or direction!! Attempted Fix: -running the commands: sudo umount -l /media/Volume_Name //-l Lazy Unmount forces the unmount sudo eject Problem: When a new CD is inserted, it is no longer mounted automatically probably because the process is still "targeting" it.

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  • Would it be useful to change java to support both static and dynamic types?

    - by James A. N. Stauffer
    What if a Java allow both static and dynamic types. That might allow the best of both worlds. i.e.: String str = "Hello"; var temp = str; temp = 10; temp = temp * 5; Would that be possible? Would that be beneficial? Do any languages currently support both and how well does it work out? Here is a better example (generics can't be used but the program does know the type): var username = HttpServletRequest.getSession().getAttribute("username");//Returns a String if(username.length() == 0) { //Error }

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  • How can I implement a download rate limited in Java?

    - by JohnWithoutArms
    Hello, I'm going to implement a (simple) downloader application in Java as a personal exercise. It is going to run several jobs in different threads, in a way that I will be downloading a few files at the same time at all times during execution. I want to be able to define a download rate limit that is shared between all the download jobs, but I don't know how to do it even for a single download task. How should I go about doing this? What are the solutions I should try implementing? Thanks.

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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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  • Concept: Information Into Memory Location.

    - by Richeve S. Bebedor
    I am having troubles conceptualizing an algorithm to be used to transform any information or data into a specific appropriate and reasonable memory location in any data structure that I will be devising. To give you an idea, I have a JPanel object instance and I created another Container type object instance of any subtype (note this is in Java because I love this language), then I collected those instances into a data structure not specifically just for those instances but also applicable to any type of object. Now my procedure for fetching those data again is to extract the object specific features similar in category to all object in that data structure and transform it into a integer data memory location (specifically as much as possible) or any type of data that will pertain to this transformation. And I can already access that memory location without further sorting or applications of O(n) time complex algorithms (which I think preferable but I wanted to do my own way XD). The data structure is of any type either binary tree, linked list, arrays or sets (and the like XD). What is important is I don't need to have successive comparing and analysis of data just to locate information in big structures. To give you a technical idea, I have to an array DS that contains JLabel object instance with a specific name "HelloWorld". But array DS contains other types of object (in multitude). Now this JLabel object has a location in the array at index [124324] (which is if you do any type of searching algorithm just to arrive at that location is conceivably slow because added to it the data structure used was an array *note please disregard the efficiency of the data structure to be used I just want to explain to you my concept XD). Now I want to equate "HelloWorld" to 124324 by using a conceptually made function applicable to all data types. So that I can do a direct search by doing this DS[extractLocation("HelloWorld")] just to get that JLabel instance. I know this may sound crazy but I want to test my concept of non-sorting feature extracting search algorithm for any data structure wherein my main problem is how to transform information to be stored into memory location of where it was stored.

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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 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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  • 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 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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  • Why is super.super.method(); not allowed in Java?

    - by Tim Büthe
    I read this question and thought that would easily be solved (not that it isn't solvable without) if one could write: @Override public String toString() { return super.super.toString(); } I'm not sure if it is useful in many cases, but I wonder why it isn't and if something like this exists in other languages. What do you guys think? EDIT: To clarify: yes I know, that's impossible to at to Java and I don't really miss it. This is nothing I expected to work and was surprised getting a compiler error. I just had the idea and like to discuss it.

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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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • Can reducing index length in Javascript associative array save memory

    - by d777
    I am trying to build a large Associative Array in JavaScript (22,000 elements). Do I need to worry about the length of the indices with regards to memory usage? In other words, which of the following options saves memory? or are they the same in memory consumption? Option 1: var student = new Array(); for (i=0; i<22000; i++) student[i] = { "studentName": token[0], "studentMarks": token[1], "studentDOB": token[2] }; Option 2: var student = new Array(); for (i=0; i<22000; i++) student[i] = { "n": token[0], "m": token[1], "d": token[2] }; I tried to test this on Google Chrome DevTools, but the numbers are inconsistent to make a decision. My best guess is that because the Array indices repeat, the browser can optimize memory usage by not repeating them for each student[i], but that is just a guess. Thanks.

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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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