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  • Variable scope and the 'using' statement in .NET

    - by pete the pagan-gerbil
    If a variable is at class level (ie, private MyDataAccessClass _dataAccess;, can it be used as part of a using statement within the methods of that class to dispose of it correctly? Is it wise to use this method, or is it better to always declare a new variable with a using statement (ie, using (MyDataAccessClass dataAccess = new MyDataAccessClass()) instead of using (_dataAccess = new MyDataAccessClass()))?

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  • Java: Difference between PrintStream and PrintWriter

    - by Martijn Courteaux
    Hi, What is the difference between PrintStream and PrintWriter? They have much methods in common. I always mix up this classes because of that reason. And I think we can use them for exactly the same. But there has to be a difference. Otherwise there was only one class. I first searched on StackOverflow, but not yet this question. Thanks

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  • Refactoring Singleton Overuse

    - by drharris
    Today I had an epiphany, and it was that I was doing everything wrong. Some history: I inherited a C# application, which was really just a collection of static methods, a completely procedural mess of C# code. I refactored this the best I knew at the time, bringing in lots of post-college OOP knowledge. To make a long story short, many of the entities in code have turned out to be Singletons. Today I realized I needed 3 new classes, which would each follow the same Singleton pattern to match the rest of the software. If I keep tumbling down this slippery slope, eventually every class in my application will be Singleton, which will really be no logically different from the original group of static methods. I need help on rethinking this. I know about Dependency Injection, and that would generally be the strategy to use in breaking the Singleton curse. However, I have a few specific questions related to this refactoring, and all about best practices for doing so. How acceptable is the use of static variables to encapsulate configuration information? I have a brain block on using static, and I think it is due to an early OO class in college where the professor said static was bad. But, should I have to reconfigure the class every time I access it? When accessing hardware, is it ok to leave a static pointer to the addresses and variables needed, or should I continually perform Open() and Close() operations? Right now I have a single method acting as the controller. Specifically, I continually poll several external instruments (via hardware drivers) for data. Should this type of controller be the way to go, or should I spawn separate threads for each instrument at the program's startup? If the latter, how do I make this object oriented? Should I create classes called InstrumentAListener and InstrumentBListener? Or is there some standard way to approach this? Is there a better way to do global configuration? Right now I simply have Configuration.Instance.Foo sprinkled liberally throughout the code. Almost every class uses it, so perhaps keeping it as a Singleton makes sense. Any thoughts? A lot of my classes are things like SerialPortWriter or DataFileWriter, which must sit around waiting for this data to stream in. Since they are active the entire time, how should I arrange these in order to listen for the events generated when data comes in? Any other resources, books, or comments about how to get away from Singletons and other pattern overuse would be helpful.

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  • Trouble swapping values as keys in generic java BST class

    - by user1729869
    I was given a generic binary search tree class with the following declaration: public class BST<K extends Comparable<K>, V> I was asked to write a method that reverses the BST such that the values become the keys and keys become values. When I call the following method (defined in the class given) reverseDict.put(originalDict.get(key), key); I get the following two error messages from Netbeans: Exception in thread "main" java.lang.RuntimeException: Uncompilable source code - Erroneous sym type: BST.put And also: no suitable method found for put(V,K) method BST.put(BST<K,V>.Node,K,V) is not applicable (actual and formal argument lists differ in length) method BST.put(K,V) is not applicable (actual argument V cannot be converted to K by method invocation conversion) where V,K are type-variables: V extends Object declared in method <K,V>reverseBST(BST<K,V>) K extends Comparable<K> declared in method <K,V>reverseBST(BST<K,V>) From what the error messages are telling me, since my values do not extend Comparable I am unable to use them as keys. If I am right, how can I get around that without changing the class given (maybe a cast)?

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  • C++ class member functions instantiated by traits

    - by Jive Dadson
    I am reluctant to say I can't figure this out, but I can't figure this out. I've googled and searched Stack Overflow, and come up empty. The abstract, and possibly overly vague form of the question is, how can I use the traits-pattern to instantiate non-virtual member functions? The question came up while modernizing a set of multivariate function optimizers that I wrote more than 10 years ago. The optimizers all operate by selecting a straight-line path through the parameter space away from the current best point (the "update"), then finding a better point on that line (the "line search"), then testing for the "done" condition, and if not done, iterating. There are different methods for doing the update, the line-search, and conceivably for the done test, and other things. Mix and match. Different update formulae require different state-variable data. For example, the LMQN update requires a vector, and the BFGS update requires a matrix. If evaluating gradients is cheap, the line-search should do so. If not, it should use function evaluations only. Some methods require more accurate line-searches than others. Those are just some examples. The original version instantiates several of the combinations by means of virtual functions. Some traits are selected by setting mode bits that are tested at runtime. Yuck. It would be trivial to define the traits with #define's and the member functions with #ifdef's and macros. But that's so twenty years ago. It bugs me that I cannot figure out a whiz-bang modern way. If there were only one trait that varied, I could use the curiously recurring template pattern. But I see no way to extend that to arbitrary combinations of traits. I tried doing it using boost::enable_if, etc.. The specialized state information was easy. I managed to get the functions done, but only by resorting to non-friend external functions that have the this-pointer as a parameter. I never even figured out how to make the functions friends, much less member functions. The compiler (VC++ 2008) always complained that things didn't match. I would yell, "SFINAE, you moron!" but the moron is probably me. Perhaps tag-dispatch is the key. I haven't gotten very deeply into that. Surely it's possible, right? If so, what is best practice?

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  • Abstract classes and Pod::Coverage

    - by Ken Williams
    I've recently started to try to use Dist::Zilla for maintaining Path::Class. I added the [PodCoverageTests] plugin, and it's reporting some failures in the Path::Class::Entity class, which is the abstract base class for Path::Class::File and Path::Class::Dir. What I'd like is some way to tell the testing code that Entity doesn't need docs, but its two derived classes do - even though the methods are only defined in the parent class. Anyone know some way to do that?

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  • How to draw a text outside rect in cocoa

    - by Kishore
    Hi, I am trying to construct a graph using cocoa.To display the points on x -axis and y- axis i used methods called drawATPoint and drawinRect which allows to draw apoint inside rect not out side . So please mention if there is any solution to display the points.I am using the following code. NSTextStorage *textStorage = [[NsTextStorage alloc]initWithString:@"0.0"]; [textStorage drawAtPoint:NSMakePoint(0,0)];

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  • Organising UI code in .NET forms

    - by sb3700
    Hi I'm someone who has taught myself programming, and haven't had any formal training in .NET programming. A while back, I started C# in order to develop a GUI program to control sensors, and the project has blossomed. I was just wondering how best to organise the code, particularly UI code, in my forms. My forms currently are a mess, or at least seem a mess to me. I have a constructor which initialises all the parameters and creates events. I have a giant State property, which updates the Enabled state of all my form control as users progress through the application (ie: disconnected, connected, setup, scanning) controlled by a States enum. I have 3-10 private variables accessed through properties, some of which have side-effects in changing the values of form elements. I have a lot of "UpdateXXX" functions to handle UI elements that depend on other UI elements - ie: if a sensor is changed, then change the baud rate drop down list. They are separated into regions I have a lot of events calling these Update functions I have a background worker which does all the scanning and analysis. My problem is this seems like a mess, particularly the State property, and is getting unmaintainable. Also, my application logic code and UI code are in the same file and to some degree, intermingled which seems wrong and means I need to do a lot of scrolling to find what I need. How do you structure your .net forms? Thanks

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  • Function Overloading

    - by Sanju
    Let us suppose i have these three methods defined: int F1(int, int); int F1(float, float); Float F1(int, int); and i am calling method F1 here: Console.writeline(F1(5,6).ToString())); Which method it will call and why?

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  • how to parse self closing tag in xml file

    - by ajay-sharma2
    Hi, I am working on an iphone application in which I am consuming a webservice. So i am parsing the XML file data. any idea about how to parse self closing tag like: State/ and how to read data of self tag like: Contact Email="[email protected]" Name="PhD" Phone="123-521-3388" Source="location"/ I am parsing xml file using NSXMLPARSER class methods and library Thanks,

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  • Is there a better way than a sequence of if's to handle events?

    - by Matt
    I recently ran across several objects implemented to handle events with a hard coded mapping using this pattern: public void handleEvent(Event event) { if(event.getCode() == SOME_STATIC_EVENT) doSomething(event); if(event.getCode() == ANOTHER_STATIC_EVENT) doSomethingElse(event); } where doSomething functions are implemented as methods of the same class. In hopes of striving for looser coupling, how would you suggest abstracting out this pattern? Also, what's the best approach for mapping 0..N functions to a fired event?

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  • Programmatically Determine If An Excel File (.xls) Contains Macros

    - by Gkakk McJkakk
    Is there any way to programmatically determine if an .xls contains macros, without actually opening it in Excel? Also are there any methods to examine which certificate (including timestamp cert) these macros are signed with? Again without using Excel. I'm wondering in particular if there are any strings that always show up in the raw data of an Excel file when macros are present.

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  • Is it OK to write a constructor which does nothing?

    - by Roman
    To use methods of a class I need to instantiate a class. At the moment the class has not constructor (so I want to write it). But than I have realized that the constructor should do nothing (I do need to specify values of fields). In this context I have a question if it is OK to write constructor which does nothing. For example: public Point() { }

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  • Remote servicve

    - by Moshik
    Hi, I have preperd a remote service, i would like to know if it's possible somehow via this service to call another activities? coz usually what ive seen so far, is how external apps calling the remote service and using it's methods, but i want vice versa.. that the remote service will call an external app's activity, thanks, moshik.

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  • Best options for image resizing

    - by Claudio Redi
    Hi, I have resize images exceeding a max size. Methods I tried so far are not good enough :-( System.Drawing.Image.GetThumbnailImage generates very poor quality images in general. Playing with options like this one I can generate better images in quality but heavier than the original one. Probably the second option (or something similar) is the best option and I would need to resize using the proper options. Any advice?

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  • calling a dynamic function in javascript

    - by scatman
    is it possible to call a dynamic method in javascript. ie suppose i have in my page 2 methods as such: function id1_add() { return 1; } function id2_add() { return 2; } i also have this function: function add() { var s1='id1'; s1+'_add()'; //??? } is it possible to call for example id1_add() in such: s1+'_add()'; so the method call depends on a previous string?

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  • algorithm to find longest non-overlapping sequences

    - by msalvadores
    I am trying to find the best way to solve the following problem. By best way I mean less complex. As an input a list of tuples (start,length) such: [(0,5),(0,1),(1,9),(5,5),(5,7),(10,1)] Each element represets a sequence by its start and length, for example (5,7) is equivalent to the sequence (5,6,7,8,9,10,11) - a list of 7 elements starting with 5. One can assume that the tuples are sorted by the start element. The output should return a non-overlapping combination of tuples that represent the longest continuos sequences(s). This means that, a solution is a subset of ranges with no overlaps and no gaps and is the longest possible - there could be more than one though. For example for the given input the solution is: [(0,5),(5,7)] equivalent to (0,1,2,3,4,5,6,7,8,9,10,11) is it backtracking the best approach to solve this problem ? I'm interested in any different approaches that people could suggest. Also if anyone knows a formal reference of this problem or another one that is similar I'd like to get references. BTW - this is not homework. Edit Just to avoid some mistakes this is another example of expected behaviour for an input like [(0,1),(1,7),(3,20),(8,5)] the right answer is [(3,20)] equivalent to (3,4,5,..,22) with length 20. Some of the answers received would give [(0,1),(1,7),(8,5)] equivalent to (0,1,2,...,11,12) as right answer. But this last answer is not correct because is shorter than [(3,20)].

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