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• Using JDBC to asynchronously read large Oracle table

  - by Ben George

  What strategies can be used to read every row in a large Oracle table, only once, but as fast as possible with JDBC & Java ? Consider that each row has non-trivial amounts of data (30 columns, including large text in some columns). Some strategies I can think of are: Single thread and read table. (Too slow, but listed for clarity) Read the id's into ConcurrentLinkedQueue, use threads to consume queue and query by id in batches. Read id's into a JMS queue, use workers to consume queue and query by id in batches. What other strategies could be used ? For the purpose of this question assume processing of rows to be free.

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• Packages organisation with MVC design pattern

  - by Oltarus

  I have been programming quite a lot now and still can't decide which of these packages hierachies was the best: package1 Class1Controller Class1Model Class1View package2 Class2Controller Class2Model Class2View or controller Class1Controller Class2Contoller model Class1Model Class2Model view Class1View Class2View In other words, is it better to apply the MVC design pattern to classes or to packages? Is there any reason to choose one over the other? My question is language-agnostic, but I'm mostly a Java programmer, if it does any difference.

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• Mono is frequently used to say "Yes, .NET is cross-platform". How valid is that claim?

  - by Thorbjørn Ravn Andersen

  In What would you choose for your project between .NET and Java at this point in time ? I say that I would consider the "Will you always deploy to Windows?" the single most important decision to make up front in a new web project, and if the answer is "no", I would recommend Java instead of .NET. A very common counter-argument is that "If we ever want to run on Linux/OS X/Whatever, we'll just run Mono", which is a very compelling argument on the surface, but I don't agree for several reasons. OpenJDK and all the vendor supplied JVM's have passed the official Sun TCK ensuring things work correctly. I am not aware of Mono passing a Microsoft TCK. Mono trails the .NET releases. What .NET-level is currently fully supported? Does all GUI elements (WinForms?) work correctly in Mono? Businesses may not want to depend on Open Source frameworks as the official plan B. I am aware that with the new governance of Java by Oracle, the future is unsafe, but e.g. IBM provides JDK's for many platforms, including Linux. They are just not open sourced. So, under which circumstances is Mono a valid business strategy for .NET-applications?

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• Inheritance vs composition in this example

  - by Gerenuk

  I'm wondering about the differences between inheritance and composition examined with concrete code relevant arguments. In particular my example was Inheritance: class Do: def do(self): self.doA() self.doB() def doA(self): pass def doB(self): pass class MyDo(Do): def doA(self): print("A") def doB(self): print("B") x=MyDo() vs Composition: class Do: def __init__(self, a, b): self.a=a self.b=b def do(self): self.a.do() self.b.do() x=Do(DoA(), DoB()) (Note for composition I'm missing code so it's not actually shorter) Can you name particular advantages of one or the other? I'm think of: composition is useful if you plan to reuse DoA() in another context inheritance seems easier; no additional references/variables/initialization method doA can access internal variable (be it a good or bad thing :) ) inheritance groups logic A and B together; even though you could equally introduce a grouped delegate object inheritance provides a preset class for the users; with composition you'd have to encapsule the initialization in a factory so that the user does have to assemble the logic and the skeleton ... Basically I'd like to examine the implications of inheritance vs composition. I heard often composition is prefered, but I'd like to understand that by example. Of course I can always start with one and refactor later to the other.

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• Finding links among many written and spoken thoughts

  - by Peter Fren

  So... I am using a digital voice recorder to record anything I see important, ranging from business to private, from rants to new business ideas. Every finalized idea is one wma-file. I wrote a program to sort the wma-files into folders. From time to time I listen to the wma-files, convert them to text(manually) and insert them into a mindmap with mindmanager, which I sort hierarchically by area and type in turn. This works very well, no idea is being lost, when I am out of ideas for a special topic, I listen to what I said and can get started again. What could a search system look like that finds links between thoughts(written in the mindmap and in the wma files) or in general gives me good search results even when the keyword I searched for is not present but a synonym of it or related topic(for instance flower should output entries containing orchid aswell, even if they contain orchid but not the very keyword flower). I prefer something ready-made but small adjustments to a given system are fine aswell. How would you approach this task?

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• Should a stack trace be in the error message presented to the user?

  - by Vilx-

  I've got a bit of an argument at my workplace and I'm trying to figure out who is right, and what is the right thing to do. Context: an intranet web application that our customers use for accounting and other ERP stuff. I'm of the opinion that an error message presented to the user (when things crash) should include as much information as possible, including the stack trace. Of course, it has to start with a nice "An Error has occurred, please submit the below information to the developers" in large, friendly letters. My reasoning is that a screenshot of the crashed application will often be the only easily available source of information. Sure, you can try to get a hold of the client's systems administrator(s), attempt to explain where your log files are, etc, but that will probably be slow and painful (talking to the client representatives mostly is). Also, having an immediate and full information is extremely useful in development, where you don't have to go hunting through the log files to find what you need on every exception. (But that could be solved with a configuration switch.) Unfortunately there has been some kind of "Security audit" (no idea how they did that without the sources... but whatever), and they complained about the full exception messages citing them as a security threat. Naturally, the clients (at least one that I know of) has taken this at face value and now demands that the messages be cleaned. I fail to see how a potential attacker could use a stack trace to figure anything out he couldn't have figured out before. Are there any examples, any documented proof of anyone ever doing that? I think that we should fight this foolish idea, but perhaps I'm the fool here, so... Who's right?

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• Linear Search in Python? [closed]

  - by POTUS

  def find_interval(mesh,x): '''This function finds the interval containing x according to the following rules, mesh is an ordered list with n numbers return 0 if x < mesh[0] return n if mesh[n-1] < x return k if mesh[k-1] <= x < mesh[k] return n-1 if mesh[n-2] <= x <= mesh[n-1] This function does a Linear search. 08/29/2012 ''' for n in range(len(mesh)): for k in range(len(mesh)): if x == mesh[n]: print "Found x at index:" return n elif x<mesh[n]: return 0 elif mesh[n-1]<x: return n elif mesh[n-2]<=x<=mesh[n-1]: return n-1 elif mesh[k-1]<=x<mesh[k]: return k mesh = [0, 0.1, 0.25, 0.5, 0.6, 0.75, 0.9, 1] print mesh print find_interval(mesh, -1) print find_interval(mesh, 0) print find_interval(mesh, 0.1) print find_interval(mesh, 0.8) print find_interval(mesh, 0.9) print find_interval(mesh, 1) print find_interval(mesh, 1.01) Output: [0, 0.100000000000000, 0.250000000000000, 0.500000000000000, 0.600000000000000, 0.750000000000000, 0.900000000000000, 1] 0 Found x at index: 0 2 6 -1 -1 0 I don't think the output is correct. Can anyone help me fix it? Thanks.

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• Help me understand a part of Java Language Specification

  - by Software Engeneering Learner

  I'm reading part 17.2.1 of Java language specification: http://docs.oracle.com/javase/specs/jls/se7/html/jls-17.html#jls-17.2.1 I won't copy a text, it's too long, but I would like to know, why for third step of sequence they're saying that If thread t was removed from m's wait set in step 2 due to an interrupt Thread couldn't get to step 2 it wasn't removed from wait set, because it written for the step 1: Thread t does not execute any further instructions until it has been removed from m's wait set Thus thread can't be removed from wait set in step 2 whatever it's due to, because it was already removed. Please help me understand this.

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• Are non Turing-complete languages considered programming languages at all?

  - by user1598390

  Reading a recent question: Is it actually possible to have a 'useful' programming language that isn't Turing complete?, I've come to wonder if non Turing-complete programming languages are considered programming languages at all. Since Turing-completeness means a language has to have variables to store values as well as control structures ( for, while )... Is a language that lacks these features considered a programming language ?

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• Trying to use OpenGL in Java on Netbeans but getting an error. Please help [migrated]

  - by Steven Rogers

  I am on a Mac running Netbeans 6.9. I downloaded and installed LWJGL using this tutorial down to the letter: http://lwjgl.org/wiki/index.php?title=Setting_Up_LWJGL_with_NetBeans I finished the installation and copied sample code to see if my system is working. I got a bug, and was not sure if it was because of faulty code or i was doing something wrong. So i shortened down the code to this little simple bit: package javaopengl; import org.lwjgl.Sys; import org.lwjgl.opengl.Display; //Testing public class Main { public static void main(String[] args) { boolean fullscreen = (args.length == 1 && args[0].equals("-fullscreen")); try { Display.create(); Display.destroy(); } catch (Exception e) { e.printStackTrace(System.err); } System.exit(0); } } But i still get the same error, this is the error that i get: run: Exception in thread "main" java.lang.NoClassDefFoundError: = Caused by: java.lang.ClassNotFoundException: = at java.net.URLClassLoader$1.run(URLClassLoader.java:202) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:190) at java.lang.ClassLoader.loadClass(ClassLoader.java:306) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301) at java.lang.ClassLoader.loadClass(ClassLoader.java:247) Java Result: 1 BUILD SUCCESSFUL (total time: 0 seconds) I am not sure what exactly is going on, Would you please tell me what is going on and how to fix it? It would be greatly appreciated, and thank you. Note: When i am looking at the text in the development environment, it does not show those red lines indicating there are any errors.

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• How do I include Implementation and Usage Documentation in one file

  - by Angelo.Hannes

  There are two types of documentation. One type, the Implementation Documentation, contains information about specific implementation of a construct (eg. Class, Method, etc.). It is targeted to the future me, maintainer, debugger and so on. And there is Usage Documentation, containing information how to use a provided api. It does not contain information about specific implementation and is targeted to users of the api. How do I include both of them in one file? (Or do I include both of them in one file? And if not, what type belongs into the source file?) Are there special techniques, using java-doc and/or best practices?

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• What's the difference between stateful and stateless?

  - by Pankaj Upadhyay

  The books and documentation on the MVC just heap on using the Stateful and Stateless terms. To be honest, i am just unable to grab the idea of it, what the books are talking about. They don't give an example to understand any of the either state, rather than just telling that HTTP is stateless and with ASP.NET MVC microsoft is going along with it. Am I missing some fundamental knowledge, as i can't understand what is stateful and why is stateful and same goes for stateless. A simple and short example that talks about a control like button or textbox can be simplify the understanding i suppose.

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• Recommened design pattern to handle multiple compression algorithms for a class hierarchy

  - by sgorozco

  For all you OOD experts. What would be the recommended way to model the following scenario? I have a certain class hierarchy similar to the following one: class Base { ... } class Derived1 : Base { ... } class Derived2 : Base { ... } ... Next, I would like to implement different compression/decompression engines for this hierarchy. (I already have code for several strategies that best handle different cases, like file compression, network stream compression, legacy system compression, etc.) I would like the compression strategy to be pluggable and chosen at runtime, however I'm not sure how to handle the class hierarchy. Currently I have a tighly-coupled design that looks like this: interface ICompressor { byte[] Compress(Base instance); } class Strategy1Compressor : ICompressor { byte[] Compress(Base instance) { // Common compression guts for Base class ... // if( instance is Derived1 ) { // Compression guts for Derived1 class } if( instance is Derived2 ) { // Compression guts for Derived2 class } // Additional compression logic to handle other class derivations ... } } As it is, whenever I add a new derived class inheriting from Base, I would have to modify all compression strategies to take into account this new class. Is there a design pattern that allows me to decouple this, and allow me to easily introduce more classes to the Base hierarchy and/or additional compression strategies?

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• Where can I find design exercises to work on?

  - by Oak

  I feel it's important to continue practicing my problem-solving skills. Writing my own mini-projects is one way, but another is to try and solve problems posted online. It's easy to find interesting programming quizzes online that require applying clever algorithms to solve - Project Euler is one well-known example. However, in a lot of real-life projects the design of the software - especially in the initial phases - has a large impact and at later stages it cannot be tweaked as easily as plain algorithms. In order to improve these skills, I'm looking for any collection of design problems. When I say "design", I mean the abstract design of a software solution - for example what modules will there be and what are the dependencies between them, how data will flow in the program, what sort of data needs to be saved in the database, etc. Design problems are those problems that are critical to solve in the early stages of any project, but their solution is a whiteboard diagram without a single line of code. Of course these sort of problems do not have a single correct solution, but I'll be especially happy with any place that also displays pros and cons of the typical solutions that might be used to approach the problem.

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• Overlap of the variable in mysql, my column are set to my query result

  - by foodil

  The question is not clear , let me clarify it: try{ $sql = ' SELECT UserID <==== (***********Used here for query ******) FROM user WHERE Rights != ?'; $stmt = $conn->prepare($sql); $stmt->execute(array('admin')); $result= $stmt->fetchAll(); } catch(PDOException $e) { die ($e->getMessage().'<a href="add.php"> Back</a>'); } foreach ($result as $set) { if ($set['UserID']==$_SESSION['username']) $rights='edit'; else {$rights=$_POST[$set['UserID']];} if (($rights != 'default' || $set['UserID']==$_SESSION['username']) && $_POST['public']==0 ) { $user=$set['UserID']; try { $query="INSERT INTO user_list(UserID <==== (***********Used here for insert ******),ListID,UserRights) VALUES ($user,$lastID,$rights)"; $stmt = $conn->prepare($query); $stmt->execute(); } catch(PDOException $e) { die ($e->getMessage().'<a href="add.php"> Back</a>'); $conn->rollBack(); } } } As you can see the UserID is a query result but it is also the column i need to insert, so when i insert into the table it will casued an error SQLSTATE[42S22]: Column not found: 1054 Unknown column 'UserA_ID' in 'field list' because the column is modify by my query result from: $query="INSERT INTO user_list(UserID,ListID,UserRights) VALUES ($user,$lastID,$rights)"; to: $query="INSERT INTO user_list(query_result_id,ListID,UserRights) VALUES ($user,$lastID,$rights)"; How to fix it ?Thank you.

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• Why is Internet Explorer the only browser to be referred to by version when talking about compatibility?

  - by Rue Leonheart

  Whenever I read something or hear someone talking about HTML5, CSS and JavaScript support, they always refer to Internet Explorer with the version number such as Internet Explorer 6, and Internet Explorer 9. But they only refer to Google Chrome, Firefox, Safari and others without version numbers. Shouldn't they also specify the version number in which certain web technologies are incompatible for other browsers instead of just Internet Explorer?

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• Is there a name for the Builder Pattern where the Builder is implemented via interfaces so certain parameters are required?

  - by Zipper

  So we implemented the builder pattern for most of our domain to help in understandability of what actually being passed to a constructor, and for the normal advantages that a builder gives. The one twist was that we exposed the builder through interfaces so we could chain required functions and unrequired functions to make sure that the correct parameters were passed. I was curious if there was an existing pattern like this. Example below: public class Foo { private int someThing; private int someThing2; private DateTime someThing3; private Foo(Builder builder) { this.someThing = builder.someThing; this.someThing2 = builder.someThing2; this.someThing3 = builder.someThing3; } public static RequiredSomething getBuilder() { return new Builder(); } public interface RequiredSomething { public RequiredDateTime withSomething (int value); } public interface RequiredDateTime { public OptionalParamters withDateTime (DateTime value); } public interface OptionalParamters { public OptionalParamters withSeomthing2 (int value); public Foo Build ();} public static class Builder implements RequiredSomething, RequiredDateTime, OptionalParamters { private int someThing; private int someThing2; private DateTime someThing3; public RequiredDateTime withSomething (int value) {someThing = value; return this;} public OptionalParamters withDateTime (int value) {someThing = value; return this;} public OptionalParamters withSeomthing2 (int value) {someThing = value; return this;} public Foo build(){return new Foo(this);} } } Example of how it's called: Foo foo = Foo.getBuilder().withSomething(1).withDateTime(DateTime.now()).build(); Foo foo2 = Foo.getBuilder().withSomething(1).withDateTime(DateTime.now()).withSomething2(3).build();

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• Need suggestion for Mutiple Windows application design

  - by King Chan

  This was previously posted in StackOverflow, I just moved to here... I am using VS2008, MVVM, WPF, Prism to make a mutiple window CRM Application. I am using MidWinow in my MainWindow, I want Any ViewModel would able to make request to MainWindow to create/add/close MidChildWindow, ChildWindow(from WPF Toolkit), Window (the Window type). ViewModel can get the DialogResult from the ChildWindow its excutes. MainWindow have control on all opened window types. Here is my current approach: I made Dictionary of each of the windows type and stores them into MainWindow class. For 1, i.e in a CustomerInformationView, its CustomerInformationViewModel can execute EditCommand and use EventAggregator to tell MainWindow to open a new ChildWindow. CustomerInformationViewModel: CustomerEditView ceView = new CustomerEditView (); CustomerEditViewModel ceViewModel = CustomerEditViewModel (); ceView.DataContext = ceViewModel; ChildWindow cWindow = new ChildWindow(); cWindow.Content = ceView; MainWindow.EvntAggregator.GetEvent<NewWindowEvent>().Publish(new WindowEventArgs(ceViewModel.ViewModeGUID, cWindow )); cWindow.Show(); Notice that all my ViewModel will generates a Guid for help identifies the ChildWindow from MainWindow's dictionary. Since I will only be using 1 View 1 ViewModel for every Window. For 2. In CustomerInformationViewModel I can get DialogResult by OnClosing event from ChildWindow, in CustomerEditViewModel can use Guid to tell MainWindow to close the ChildWindow. Here is little question and problems: Is it good idea to use Guid here? Or should I use HashKey from ChildWindow? My MainWindows contains windows reference collections. So whenever window close, it will get notifies to remove from the collection by OnClosing event. But all the Windows itself doesn't know about its associated Guid, so when I remove it, I have to search for every KeyValuePair to compares... I still kind of feel wrong associate ViewModel's Guid for ChildWindow, it would make more sense if ChildWindow has it own ID then ViewModel associate with it... But most important, is there any better approach on this design? How can I improve this better?

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• APIs that deal with logins

  - by Brandon Still

  I have been asked to make a mobile app for a friends website. The website is a Multi level marketing site that sells products and franchises. A client logs in in to the website and can view his or her dashboard ( user can view team members, business volume, commissions, invoices, etc.) The app is supposed to bring the dashboard to user's mobile devices (w/ some added features). The company does not have any APIs that deal with interaction or authentication, and I am new to the whole secure login side of app development. My questions is this, how do I let the users gain access to their information via my app from the secure website when there is no API?

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• Carrer path as Java developer for non Btech or BCA background graduate [closed]

  - by Piyush Jolly

  My name is Piyush and I'm a graduate in Bsc. multimedia. Now I'm planing to learn JAVA and take it as my carrier and there are few things I'm really worried about:- 1)Does the industry accepts graduates from Non-it background. 2)Because my course was all about 3D Animation nothing like software programing was taught to us and I have been doing programing in c from long time just because i liked it so now i want to purse my carrier as programmer. 3)From where should I learn, which Institute should I refer to who teaches the Java from the basic. 4)What kind of jobs I can expect after the completion of the course. I'm from Delhi. Any help will be much appreciated. Regards Piyush Jolly

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• Monitoring C++ applications

  - by Scott A

  We're implementing a new centralized monitoring solution (Zenoss). Incorporating servers, networking, and Java programs is straightforward with SNMP and JMX. The question, however, is what are the best practices for monitoring and managing custom C++ applications in large, heterogenous (Solaris x86, RHEL Linux, Windows) environments? Possibilities I see are: Net SNMP Advantages single, central daemon on each server well-known standard easy integration into monitoring solutions we run Net SNMP daemons on our servers already Disadvantages: complex implementation (MIBs, Net SNMP library) new technology to introduce for the C++ developers rsyslog Advantages single, central daemon on each server well-known standard unknown integration into monitoring solutions (I know they can do alerts based on text, but how well would it work for sending telemetry like memory usage, queue depths, thread capacity, etc) simple implementation Disadvantages: possible integration issues somewhat new technology for C++ developers possible porting issues if we switch monitoring vendors probably involves coming up with an ad-hoc communication protocol (or using RFC5424 structured data; I don't know if Zenoss supports that without custom Zenpack coding) Embedded JMX (embed a JVM and use JNI) Advantages consistent management interface for both Java and C++ well-known standard easy integration into monitoring solutions somewhat simple implementation (we already do this today for other purposes) Disadvantages: complexity (JNI, thunking layer between native C++ and Java, basically writing the management code twice) possible stability problems requires a JVM in each process, using considerably more memory JMX is new technology for C++ developers each process has it's own JMX port (we run a lot of processes on each machine) Local JMX daemon, processes connect to it Advantages single, central daemon on each server consistent management interface for both Java and C++ well-known standard easy integration into monitoring solutions Disadvantages: complexity (basically writing the management code twice) need to find or write such a daemon need a protocol between the JMX daemon and the C++ process JMX is new technology for C++ developers CodeMesh JunC++ion Advantages consistent management interface for both Java and C++ well-known standard easy integration into monitoring solutions single, central daemon on each server when run in shared JVM mode somewhat simple implementation (requires code generation) Disadvantages: complexity (code generation, requires a GUI and several rounds of tweaking to produce the proxied code) possible JNI stability problems requires a JVM in each process, using considerably more memory (in embedded mode) Does not support Solaris x86 (deal breaker) Even if it did support Solaris x86, there are possible compiler compatibility issues (we use an odd combination of STLPort and Forte on Solaris each process has it's own JMX port when run in embedded mode (we run a lot of processes on each machine) possibly precludes a shared JMX server for non-C++ processes (?) Is there some reasonably standardized, simple solution I'm missing? Given no other reasonable solutions, which of these solutions is typically used for custom C++ programs? My gut feel is that Net SNMP is how people do this, but I'd like other's input and experience before I make a decision.

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• I'm a CS student, and honestly, I don't understand Knuth's books

  - by Raymond Ho

  I stumbled upon this quote from Bill Gates: "You should definitely send me a resume if you can read the whole thing." He was talking about The Art of Programming books. So I was pretty curious and want to read it all. But honestly, I don't understand it. I'm really not that intellectual. So this should be the reason why I can't understand it, but I am eager to learn. I'm currently reading Volume 1 about fundamental algorithms. Are there any books out there that are friendly for novices/slow people like me, which would help to build up my knowledge so that I can read Knuth's book with ease in the future?

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• Which is the most practical way to add functionality to this piece of code?

  - by Adam Arold

  I'm writing an open source library which handles hexagonal grids. It mainly revolves around the HexagonalGrid and the Hexagon class. There is a HexagonalGridBuilder class which builds the grid which contains Hexagon objects. What I'm trying to achieve is to enable the user to add arbitrary data to each Hexagon. The interface looks like this: public interface Hexagon extends Serializable { // ... other methods not important in this context <T> void setSatelliteData(T data); <T> T getSatelliteData(); } So far so good. I'm writing another class however named HexagonalGridCalculator which adds some fancy pieces of computation to the library like calculating the shortest path between two Hexagons or calculating the line of sight around a Hexagon. My problem is that for those I need the user to supply some data for the Hexagon objects like the cost of passing through a Hexagon, or a boolean flag indicating whether the object is transparent/passable or not. My question is how should I implement this? My first idea was to write an interface like this: public interface HexagonData { void setTransparent(boolean isTransparent); void setPassable(boolean isPassable); void setPassageCost(int cost); } and make the user implement it but then it came to my mind that if I add any other functionality later all code will break for those who are using the old interface. So my next idea is to add annotations like @PassageCost, @IsTransparent and @IsPassable which can be added to fields and when I'm doing the computation I can look for the annotations in the satelliteData supplied by the user. This looks flexible enough if I take into account the possibility of later changes but it uses reflection. I have no benchmark of the costs of using annotations so I'm a bit in the dark here. I think that in 90-95% of the cases the efficiency is not important since most users wont't use a grid where this is significant but I can imagine someone trying to create a grid with a size of 5.000.000.000 X 5.000.000.000. So which path should I start walking on? Or are there some better alternatives? Note: These ideas are not implemented yet so I did not pay too much attention to good names.

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• Working with a company as a Junior Developer [closed]

  - by user1601973

  We all have started our careers in some way or other. Well, I am a college student based in North America & I am doing my second internship with the same company with which I did my first internship. I came back here because people here were helpful always and supportive. But it just happened today, and I wanted to share this on SO. Well since I started I have been doing documentation and that kind of stuff only as compared to my first internship in which I actually worked along with the developers & learned so many things. Well, I was in a conversation with my Team lead, and he asked me if I completed that particular work or not? Well, That particular work had slipped from my mind. He was indeed I kind of pissed, and said "You don't have to worry about it, I will figure out". Well, I felt so bad and was about to literally cry. I stopped my lunch and then went on to complete that work. I always ask for work in office, and I always try to be an asset for whoever I am working but this was the first time that it happened. What are your thoughts on this and should I apologise or not? I think I should.

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• How do you encode Algebraic Data Types in a C#- or Java-like language?

  - by Jörg W Mittag

  There are some problems which are easily solved by Algebraic Data Types, for example a List type can be very succinctly expressed as: data ConsList a = Empty | ConsCell a (ConsList a) consmap f Empty = Empty consmap f (ConsCell a b) = ConsCell (f a) (consmap f b) l = ConsCell 1 (ConsCell 2 (ConsCell 3 Empty)) consmap (+1) l This particular example is in Haskell, but it would be similar in other languages with native support for Algebraic Data Types. It turns out that there is an obvious mapping to OO-style subtyping: the datatype becomes an abstract base class and every data constructor becomes a concrete subclass. Here's an example in Scala: sealed abstract class ConsList[+T] { def map[U](f: T => U): ConsList[U] } object Empty extends ConsList[Nothing] { override def map[U](f: Nothing => U) = this } final class ConsCell[T](first: T, rest: ConsList[T]) extends ConsList[T] { override def map[U](f: T => U) = new ConsCell(f(first), rest.map(f)) } val l = (new ConsCell(1, new ConsCell(2, new ConsCell(3, Empty))) l.map(1+) The only thing needed beyond naive subclassing is a way to seal classes, i.e. a way to make it impossible to add subclasses to a hierarchy. How would you approach this problem in a language like C# or Java? The two stumbling blocks I found when trying to use Algebraic Data Types in C# were: I couldn't figure out what the bottom type is called in C# (i.e. I couldn't figure out what to put into class Empty : ConsList< ??? >) I couldn't figure out a way to seal ConsList so that no subclasses can be added to the hierarchy What would be the most idiomatic way to implement Algebraic Data Types in C# and/or Java? Or, if it isn't possible, what would be the idiomatic replacement?

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