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• What's an elegant solution to get the property values from two classes (that have the same property

  - by SlipToFall

  Essentially I have to deal with a poorly implemented web service. They have two classes that don't derive from a parent class, but have the same properties (Ughh...). So it looks like this in my web service proxy class file: public partial class Product1 { public int Quantity; public int Price; } public partial class Product2 { public int Quantity; public int Price; } So what's the best way to grab the values from known properties without duplicating the code and casting to their respective classes? I know I probably could use reflection, but that can get ugly. If there is an easier less crazier way to do it (maybe in the new c# features?) please let me know.

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• class which cannot be derived

  - by benjamin button

  I found this code here class Usable; class Usable_lock { friend class Usable; private: Usable_lock() {} Usable_lock(const Usable_lock&) {} }; class Usable : public virtual Usable_lock { // ... public: Usable(); Usable(char*); // ... }; Usable a; class DD : public Usable { }; DD dd; // error: DD::DD() cannot access // Usable_lock::Usable_lock(): private member Could anybody explain me this code?

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• How to generalize a method call in Java (to avoid code duplication)

  - by dln385

  I have a process that needs to call a method and return its value. However, there are several different methods that this process may need to call, depending on the situation. If I could pass the method and its arguments to the process (like in Python), then this would be no problem. However, I don't know of any way to do this in Java. Here's a concrete example. (This example uses Apache ZooKeeper, but you don't need to know anything about ZooKeeper to understand the example.) The ZooKeeper object has several methods that will fail if the network goes down. In this case, I always want to retry the method. To make this easy, I made a "BetterZooKeeper" class that inherits the ZooKeeper class, and all of its methods automatically retry on failure. This is what the code looked like: public class BetterZooKeeper extends ZooKeeper { private void waitForReconnect() { // logic } @Override public Stat exists(String path, Watcher watcher) { while (true) { try { return super.exists(path, watcher); } catch (KeeperException e) { // We will retry. } waitForReconnect(); } } @Override public byte[] getData(String path, boolean watch, Stat stat) { while (true) { try { return super.getData(path, watch, stat); } catch (KeeperException e) { // We will retry. } waitForReconnect(); } } @Override public void delete(String path, int version) { while (true) { try { super.delete(path, version); return; } catch (KeeperException e) { // We will retry. } waitForReconnect(); } } } (In the actual program there is much more logic and many more methods that I took out of the example for simplicity.) We can see that I'm using the same retry logic, but the arguments, method call, and return type are all different for each of the methods. Here's what I did to eliminate the duplication of code: public class BetterZooKeeper extends ZooKeeper { private void waitForReconnect() { // logic } @Override public Stat exists(final String path, final Watcher watcher) { return new RetryableZooKeeperAction<Stat>() { @Override public Stat action() { return BetterZooKeeper.super.exists(path, watcher); } }.run(); } @Override public byte[] getData(final String path, final boolean watch, final Stat stat) { return new RetryableZooKeeperAction<byte[]>() { @Override public byte[] action() { return BetterZooKeeper.super.getData(path, watch, stat); } }.run(); } @Override public void delete(final String path, final int version) { new RetryableZooKeeperAction<Object>() { @Override public Object action() { BetterZooKeeper.super.delete(path, version); return null; } }.run(); return; } private abstract class RetryableZooKeeperAction<T> { public abstract T action(); public final T run() { while (true) { try { return action(); } catch (KeeperException e) { // We will retry. } waitForReconnect(); } } } } The RetryableZooKeeperAction is parameterized with the return type of the function. The run() method holds the retry logic, and the action() method is a placeholder for whichever ZooKeeper method needs to be run. Each of the public methods of BetterZooKeeper instantiates an anonymous inner class that is a subclass of the RetryableZooKeeperAction inner class, and it overrides the action() method. The local variables are (strangely enough) implicitly passed to the action() method, which is possible because they are final. In the end, this approach does work and it does eliminate the duplication of the retry logic. However, it has two major drawbacks: (1) it creates a new object every time a method is called, and (2) it's ugly and hardly readable. Also I had to workaround the 'delete' method which has a void return value. So, here is my question: is there a better way to do this in Java? This can't be a totally uncommon task, and other languages (like Python) make it easier by allowing methods to be passed. I suspect there might be a way to do this through reflection, but I haven't been able to wrap my head around it.

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• how to run the dependecy class file in java

  - by Manu

  I have created Excel Sheet using java program.It works fine. My problem is, i have copied the .class file into other directory with the necessary jar files need to create this excel sheet, for example my .class is inside "pack" package. c:/myprogram/pack/excelprogram.class to d:/myprogram /pack/excelprogram.class /jxl.jar /ojdbc14.jar if i run the program javac pack.excelprogram it display below error Caused by: java.lang.ClassNotFoundException: jxl.format.CellFormat i have dependency jar file(jxl.jar) for this excel sheet creation.Error is displaying from that only. i have set class path for this jar file like set classpath="%classpath%";d:/myprogram/jxl.jar;d:/myprogram/ojdbc14.jar;.; even though i'm getting the same error. Please help ASAP.

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• Which class will be instantiated

  - by Michael

  Say I have 2 subclasses from UIViewController, class A and class B. In Main nib file an object is representing class A and it is set to load file from Secondary nib file. The owner of Secondary nib is of class B. The question is - from which class an object in Main nib file will be instanciated once the nib files unarchived in the memory? The reason this question arised is that I have to take care myself if such reference to external NIB file present, to ensure that the first nib's object and second nib's owner is same. Please correct me if my statement is wrong.

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• Access outer class from inner class: Why is it done this way?

  - by Vuntic

  So most of us know how to access an outer class from an inner class. Searches with those words give oodles of answered questions on that topic. But what I want to know is why the syntax is the way it is. Example: public class A { private class B { public void c() {A.this.d();} } public void d() {System.out.println("You've called d()! Go, you!");} } Why is it A.this.d()? It looks like this is a static field of class A, but... * am confused * Forgive me if this is a repeat; like I said, searches with those words give how-answers.

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• Group properties in custom control

  - by Gunners98

  I want to do a class that have properties like font, which will have other properties, such as name, size, unit,bold.I had tried a solution but it isn't working for me.(http://stackoverflow.com/questions/755391/group-properties-in-a-custom-control) Anyone can help? Any help will be appreciated. <TypeConverter(GetType(ExpandableObjectConverter))> _ Class TestingClass 'Some property here End Class

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• Consistency in placing operator functions

  - by wrongusername

  I have a class like this: class A { ...private functions, variables, etc... public: ...some public functions and variables... A operator * (double); A operator / (double); A operator * (A); ...and lots of other operators } However, I want to also be able to do stuff like 2 * A instead of only being allowed to do A * 2, and so I would need functions like these outside of the class: A operator * (double, A); A operator / (double, A); ...etc... Should I put all these operators outside of the class for consistency, or should I keep half inside and half outside?

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• Casting Class into String and Vice Versa in JAVA

  - by topgun_ivard

  I have a program in which I need to store a Class object into memory by casting it into String. Is it possible to convert the String back into the original Class so that I can use that class variables? I am doing this in JAVA. Example: test.java class hello{ public String h1; public String h2; } public class test { public static void main(String[] args) { hello h = new hello(); h.h1 = "hello"; h.h2 = "world"; String s = h.toString(); System.out.println("Print s : "+s); // Now I need to convert String s into type hello so that // I can do this: // (hello)s.h1; // (hello)s.h2; } } NOTE: this is not a homework, this is a personal project and I would be grateful if anyone can help! Thanks! Ivar

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• Can I write to different jetty databases using JPA that is using the same "entity class"

  - by Per

  I am using Java persistance and there EntityManager class and have it assigned to storage a class object that shall be written to the database. My problem is that I want to write to different databases using the same storage class. My solution to that was to write a StorageManagerfactory that has a Map holding all EntityManagers. The solution looked good until I looked at the databases and realized that all information (undepending of the Map, which gets the correct value) was written to the same database (one of the initialised in the Map). So my question is: Can I write to different databases using JPA that is using the same storage class (the class holding the structure of my database)? Thanks

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• Subprocess with variables & Command from different class

  - by Pastelinux

  source: http://pastebin.com/utL7Ebeq My thinking is that if i run from controller class "main" it will allow me to take the "data" from Class "model", def "filename". It doesn't seem to work. As you can see below what i mean class Controller: def __init__(self): self.model = Model() self.view = View() def main(self): data = self.model.filename() self.view.tcpdump(data) class View: def tcpdump(self, command): subprocess.call(command.split(), shell=False) When i run my code i get this error: subprocess.call(command.split(), shell=False) AttributeError: 'NoneType' object has no attribute 'split' My guess means that its not picking up command (look at source for reference) or that its not getting command with variables. But i know the error when variables are not being picked up so i don't think it is that. My question is, from what i have thus far, how do i from "class view" grab "command" for my subprocesses to run. Thanks~ John Riselvato

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• Calling a network State check from other activities

  - by Laurent

  I realize this question has been answered before but couldn't find an answer that deals with my specific case. I want to create a class called "InternetConnectionChecks" that will handle checking a network state and http timeouts. I'll call the methods twice in the app (once at the beginning to get data from a server, and once at the end to send user orders to the server). For good form I'd like to put all these methods in a single class rather than copy/paste at different points in my code. To check the network state, I'm using ConnectivityManager; thing is, getSystemService requires a class that extends Activity. package arbuckle.app; import android.app.Activity; import android.app.Service; import android.content.Context; import android.net.ConnectivityManager; import android.net.NetworkInfo; public class InternetConnectionChecks extends Activity { public boolean isNetworkAvailable(){ ConnectivityManager connectivityManager = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE); NetworkInfo activeNetworkInfo = connectivityManager.getActiveNetworkInfo(); if ((activeNetworkInfo != null)&&(activeNetworkInfo.isConnected())){ return true; }else{ return false; } } } QUESTION: if I call the method isNetworkAvailable from another activity, am I: - going to hit up serious errors. - violating good coding form? *If this isn't the right way to do things, can you point me in the right direction to set up a separate class I can call on to check internet connection? Thanks everyone!

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• jQuery plugin and prototype class

  - by Shanison

  Hi I am converting some prototype javascript to jQuery javascript. In prototype we can do Class.create to create a class. However, jQuery doesn't provide this. So I was thinking to rewrite the class into a jQuery plugin. Is this the best practice? My concern is that if I do all for the class, then I will add a lot of things to jQuery object. The other alternative is to use some extra lines of codes I found http://ejohn.org/blog/simple-javascript-inheritance/#postcomment. Then you can do the following: var Person = Class.extend({ init: function(isDancing){ this.dancing = isDancing; }, dance: function(){ return this.dancing; } }); Which one is better, please advise. Thank you very much!

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• C# Inconsistent Accessibility (Multiple Classes)

  - by MattP

  I am getting an Inconsistent Accessibility problem where I have one class that contains a List of another class namespace NS { public class Foo { public Foo() { this.bar = new List<Bar>(); } private List<Bar> bar; } public class Bar { public Bar() { } } } The error is property type NS.Bar is less accessible than property NS.Foo.Bar The structure to the application is each Foo consists of a Dynamic Array (List) of Bar. It's not ecommerce but the best example would be an eCommerce Store-Categories-Products in terms of how the data will be accessed.

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• I serialized a C++ object, how to allocate memory for it without knowing what type it is?

  - by Neo_b

  Hello, I have serialized a C++ object and I wish to allocate space for it, although I can't use the "new" operator, because I do not know the object's class. I tried using malloc(sizeof(object)), although trying to typecast the pointer to the type the serialized object is of, the program shut down. Where is the information about the object class stored? class object { public: virtual void somefunc(); int someint; }; class objectchild:public object { } object *o=(object*)malloc(sizeof(objectchild)); cout << int(dynamic_cast<objectchild*>(o)) << endl; This causes a program shutdown. Thank you in advance.

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• how to access child instances in a vector in c++

  - by tsubasa

  I have a parent class and child class (inherited from parent). In the child class, I have a member function named function_blah(); I used vector<parent*> A to store 5 parent instances, 3 child instances. So the total number of elements in the vector is 8. I can easily access to member functions of element A[0] to A[4], which are parent instances. But whenever I try to have access to member functions of element A[5] to A[7], the compiler complains that class parent has no member named 'function_blah' The way I access to elements is using index. e.x A[i] with i = 0..7. Is it correct? if not, how?

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• How the existing data to be if entity structure modified or deleted on GAE?

  - by Eonil

  GAE recommends using JDO/JPA. But I have serious question about using OODB like them. JDO based on user's class structure. And data structure should be modified continually as service advances. So, If data(entity) class property being removed, what happened to existing data on the property? If data(entity) class renamed for refactoring reason, how the JDO know those renaming? Or all data loss? Major point is "How JDO/GAE/BigTable applies modification of class into existing entity structure and data?".

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• Java - Confused by the one class per file rule

  - by Mark

  The one class per file rule in Java has me a bit confused. I writing an Android app and trying to implement the accepted answer to this question: Common class for AsyncTask in Android? which calls for an interface definition which class A implements and class B accepts as an argument to its constructor. So I need an A.java and a B.java, but where does the interface go? Does it need a separate java file itself? Do I have to define it inside both A and B? If not how to import it? Also I will have about 10 different AsyncTask classes, but I don't want to bother creating a new file for each one. What would you recommend? Is there a way to put all 10 classes in one file? Or should I create a big if/then block inside the class and pass an argument telling it which of the 10 different tasks I want it to do?

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• Does database affect classes?

  - by satyanarayana

  I had created one class User and UserDAOImpl class for querying DB using class User. As there is one table to be queried, these two classes are sufficient for me. What if there is a case where new fields are to be added to that one table is to be divided into 3 tables( user_info, user_profile and user_address) to store user? As new fields are added, I need to change classes User and UserDAOImpl, it seems these two are not sufficient. It seems database changes affect my classes. In this case, do I need to divide class User into 3 classes as tables are changes? Can any one suggest me how can I solve this without making too many changes?

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• c# class design - what can I use instead of "static abstract"?

  - by Ryan

  I want to do the following public abstract class MyAbstractClass { public static abstract int MagicId { get; } public static void DoSomeMagic() { // Need to get the MagicId value defined in the concrete implementation } } public class MyConcreteClass : MyAbstractClass { public static override int MagicId { get { return 123; } } } However I can't because you can't have static abstract members. I understand why I can't do this - any recommendations for a design that will achieve much the same result? (For clarity - what I am trying to do is provide a library with an abstract base class but the concrete versions MUST implement a few properties/methods themselves and yes, there are good reasons for keeping it static.)

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• Which other event handler than click could i use?

  - by Gaelle

  I have a jQuery question, and I really think it is a silly one : i'm a beginner in JS and jQuery... I'm using $("#myLink").click(function(){ $(".myClassToShow").show(); $(".myClassToHide").hide(); }); to hide elements with class myClassToHide as a class attribute and show elements with class myClassToShow as a class attribute. I think this is really easy to understand :) I didn't think it would hide every elements with the good class, but, well, it works. My worry here is that my elements show and hide only for few seconds : the time my mouse click on the link. I would like to make myClassToShow elements remaining on the screen, when i already clicked my link, and myClassToHide elements really hide. For example, on the johann Hammarstrom's website, when you click on "Print", all his works which are not print gone hide, and only the printing one remain. That's kinda what i want. I searched using Firebug, but couldn't find which kind of event he used. I know a onchange is not the correct answer, so what? Could you help me please?

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• Delphi 2010 - Why can't I declare an abstract method with a generic type parameter?

  - by James

  I am trying to do the following in Delphi 2010: TDataConverter = class abstract public function Convert<T>(const AData: T): string; virtual; abstract; end; However, I keep getting the following compiler error: E2533 Virtual, dynamic and message methods cannot have type parameters I don't quite understand the reason why I can't do this. I can do this in C# e.g. public abstract class DataConverter { public abstract string Convert<T>(T data); } Anyone know the reasoning behind this?

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• TypoScript: {field:uid} replacement not working | Different CSS class per menu item

  - by Alex

  I have a header menu and try to define different CSS classes for each item. This is what I have: 20 = HMENU 20 { special = directory special.value = 107 1 = TMENU 1 { wrap = <ul class="foo" id="mymenu">|</ul> expAll = 1 NO = 1 NO.allWrap = <li class="first menu_{field:uid}">|</li> || <li class="menu_{field:uid}">|</li> || <li class="last menu_{field:uid}">|</li> } } But in the HTML output I simply get class="first menu_{field:uid}" and nothing is replaced.

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• Does the Liskov Substitution Principle apply to subtype which inherited from abstract class?

  - by A.A.

  loosely speaking, Liskov Substitution Principle states that a derived class can be substitute in place of the base class without affecting the user. In the case when the base class is an abstract class, which means no user is using an instance of the base class, does the Liskov inheritance restrictions still apply to the derived class?

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• Operator & and * at function prototype in class

  - by Puyover

  I'm having a problem with a class like this: class Sprite { ... bool checkCollision(Sprite &spr); ... }; So, if I have that class, I can do this: ball.checkCollision(bar1); But if I change the class to this: class Sprite { ... bool checkCollision(Sprite* spr); ... }; I have to do this: ball.checkCollision(&bar1); So, what's the difference?? It's better a way instead other? Thank you.

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