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• Enclosing service execution in try-catch: bad practice?

  - by Sorin Comanescu

  Hi, Below is the usual Program.cs content for a windows service program: static class Program { /// <summary> /// The main entry point for the application. /// </summary> static void Main() { ServiceBase[] ServicesToRun; ServicesToRun = new ServiceBase[] { new MyService() }; ServiceBase.Run(ServicesToRun); } } Is it a bad practice to enclose the ServiceBase.Run(...) in a try-catch block? Thanks.

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• Why is Flash so hard on the CPU?

  - by CodeToGlory

  Recently I hear Steve Jobs citing this as a main reason to not have Flash on IPADS

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• Multiple forms in delphi

  - by Hendriksen123

  In my Delphi Project i want to have a 'Settings' button that when clicked, opens a second form (i think this is the correct term, i essentially want a new window to open) for settings. When the user has finished changing the settings on this new form, i want the form to close on a button click. The settings the user types in will also need to be accessible to the first, 'main' form. So, for example, if my programme consisted of a main form, that calculated 'A' + 'B' (A and B being integer variables), with the settings form allowing the user to set values for A and B, how would i do this?

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• compiler warning at C++ template base class

  - by eike

  I get a compiler warning, that I don't understand in that context, when I compile the "Child.cpp" from the following code. (Don't wonder: I stripped off my class declarations to the bare minuum, so the content will not make much sense, but you will see the problem quicker). I get the warning with VS2003 and VS2008 on the highest warning level. The code AbstractClass.h : #include <iostream> template<typename T> class AbstractClass { public: virtual void Cancel(); // { std::cout << "Abstract Cancel" << std::endl; }; virtual void Process() = 0; }; //outside definition. if I comment out this and take the inline //definition like above (currently commented out), I don't get //a compiler warning template<typename T> void AbstractClass<T>::Cancel() { std::cout << "Abstract Cancel" << std::endl; } Child.h : #include "AbstractClass.h" class Child : public AbstractClass<int> { public: virtual void Process(); }; Child.cpp : #include "Child.h" #include <iostream> void Child::Process() { std::cout << "Process" << std::endl; } The warning The class "Child" is derived from "AbstractClass". In "AbstractClass" there's the public method "AbstractClass::Cancel()". If I define the method outside of the class body (like in the code you see), I get the compiler warning... AbstractClass.h(7) : warning C4505: 'AbstractClass::Cancel' : unreferenced local function has been removed with [T=int] ...when I compile "Child.cpp". I do not understand this, because this is a public function and the compiler can't know if I later reference this method or not. And, in the end, I reference this method, because I call it in main.cpp and despite this compiler warning, this method works if I compile and link all files and execute the program: //main.cpp #include <iostream> #include "Child.h" int main() { Child child; child.Cancel(); //works, despite the warning } If I do define the Cancel() function as inline (you see it as out commented code in AbstractClass.h), then I don't get the compiler warning. Of course my program works, but I want to understand this warning or is this just a compiler mistake? Furthermore, if do not implement AbsctractClass as a template class (just for a test purpose in this case) I also don't get the compiler warning...?

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• Rationale behind Python's preferred for syntax

  - by susmits

  What is the rationale behind the advocated use of the for i in xrange(...)-style looping constructs in Python? For simple integer looping, the difference in overheads is substantial. I conducted a simple test using two pieces of code: File idiomatic.py: #!/usr/bin/env python M = 10000 N = 10000 if __name__ == "__main__": x, y = 0, 0 for x in xrange(N): for y in xrange(M): pass File cstyle.py: #!/usr/bin/env python M = 10000 N = 10000 if __name__ == "__main__": x, y = 0, 0 while x < N: while y < M: y += 1 x += 1 Profiling results were as follows: bash-3.1$ time python cstyle.py real 0m0.109s user 0m0.015s sys 0m0.000s bash-3.1$ time python idiomatic.py real 0m4.492s user 0m0.000s sys 0m0.031s I can understand why the Pythonic version is slower -- I imagine it has a lot to do with calling xrange N times, perhaps this could be eliminated if there was a way to rewind a generator. However, with this deal of difference in execution time, why would one prefer to use the Pythonic version?

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• How different is Objective-C from C++?

  - by Alerty

  What are the main differences between Objective-C and C++ in terms of the syntax, features, paradigms, frameworks and libraries?

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• importing same module more than once

  - by wallacoloo

  So after a few hours, I discovered the cause of a bug in my application. My app's source is structure like: main/ __init__.py folderA/ __init__.py fileA.py fileB.py Really, there are about 50 more files. But that's not the point. In main/__init__.py, I have this code: from folderA.fileA import * in folderA/__init__.py I have this code: sys.path.append(pathToFolderA) in folderA/fileB.py I have this code: from fileA import * The problem is that fileA gets imported twice. However, I only want to import it once. The obvious way to fix this (to me atleast) is to change certain paths from path to folderA.path But I feel like Python should not even have this error in the first place. What other workarounds are there that don't require each file to know it's absolute location?

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• NSNumber >= 13 won't retain. Everything else will.

  - by jkap

  The code I'm currently working on requires adding an NSNumber object to an array. All of the NSNumbers with value 0-12 are added fine, but 13 onward causes a EXC_BAD_ACCESS. I turned on NSZombieEnabled and am now getting *** -[CFNumber retain]: message sent to deallocated instance 0x3c78420. Here's the call stack: #0 0x01eac3a7 in ___forwarding___ #1 0x01e886c2 in __forwarding_prep_0___ #2 0x01e3f988 in CFRetain #3 0x01e4b586 in _CFArrayReplaceValues #4 0x0002a2f9 in -[NSCFArray insertObject:atIndex:] #5 0x0002a274 in -[NSCFArray addObject:] #6 0x00010a3b in -[Faves addObject:] at Faves.m:24 #7 0x000062ff in -[ShowController processFave] at ShowController.m:458 #8 0x002af405 in -[UIApplication sendAction:to:from:forEvent:] #9 0x00312b4e in -[UIControl sendAction:to:forEvent:] #10 0x00314d6f in -[UIControl(Internal) _sendActionsForEvents:withEvent:] #11 0x00313abb in -[UIControl touchesEnded:withEvent:] #12 0x002c8ddf in -[UIWindow _sendTouchesForEvent:] #13 0x002b27c8 in -[UIApplication sendEvent:] #14 0x002b9061 in _UIApplicationHandleEvent #15 0x02566d59 in PurpleEventCallback #16 0x01e83b80 in CFRunLoopRunSpecific #17 0x01e82c48 in CFRunLoopRunInMode #18 0x02565615 in GSEventRunModal #19 0x025656da in GSEventRun #20 0x002b9faf in UIApplicationMain #21 0x00002498 in main at main.m:14 If it wasn't isolated to NSNumbers of a certain range, I'd assume I screwed something up with my memory management, but I've just got no idea. Any ideas? Thanks, Josh

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• Prim's MST algorithm implementation with Java

  - by user1290164

  I'm trying to write a program that'll find the MST of a given undirected weighted graph with Kruskal's and Prim's algorithms. I've successfully implemented Kruskal's algorithm in the program, but I'm having trouble with Prim's. To be more precise, I can't figure out how to actually build the Prim function so that it'll iterate through all the vertices in the graph. I'm getting some IndexOutOfBoundsException errors during program execution. I'm not sure how much information is needed for others to get the idea of what I have done so far, but hopefully there won't be too much useless information. This is what I have so far: I have a Graph, Edge and a Vertex class. Vertex class mostly just an information storage that contains the name (number) of the vertex. Edge class can create a new Edge that has gets parameters (Vertex start, Vertex end, int edgeWeight). The class has methods to return the usual info like start vertex, end vertex and the weight. Graph class reads data from a text file and adds new Edges to an ArrayList. The text file also tells us how many vertecis the graph has, and that gets stored too. In the Graph class, I have a Prim() -method that's supposed to calculate the MST: public ArrayList<Edge> Prim(Graph G) { ArrayList<Edge> edges = G.graph; // Copies the ArrayList with all edges in it. ArrayList<Edge> MST = new ArrayList<Edge>(); Random rnd = new Random(); Vertex startingVertex = edges.get(rnd.nextInt(G.returnVertexCount())).returnStartingVertex(); // This is just to randomize the starting vertex. // This is supposed to be the main loop to find the MST, but this is probably horribly wrong.. while (MST.size() < returnVertexCount()) { Edge e = findClosestNeighbour(startingVertex); MST.add(e); visited.add(e.returnStartingVertex()); visited.add(e.returnEndingVertex()); edges.remove(e); } return MST; } The method findClosesNeighbour() looks like this: public Edge findClosestNeighbour(Vertex v) { ArrayList<Edge> neighbours = new ArrayList<Edge>(); ArrayList<Edge> edges = graph; for (int i = 0; i < edges.size() -1; ++i) { if (edges.get(i).endPoint() == s.returnVertexID() && !visited(edges.get(i).returnEndingVertex())) { neighbours.add(edges.get(i)); } } return neighbours.get(0); // This is the minimum weight edge in the list. } ArrayList<Vertex> visited and ArrayList<Edges> graph get constructed when creating a new graph. Visited() -method is simply a boolean check to see if ArrayList visited contains the Vertex we're thinking about moving to. I tested the findClosestNeighbour() independantly and it seemed to be working but if someone finds something wrong with it then that feedback is welcome also. Mainly though as I mentioned my problem is with actually building the main loop in the Prim() -method, and if there's any additional info needed I'm happy to provide it. Thank you. Edit: To clarify what my train of thought with the Prim() method is. What I want to do is first randomize the starting point in the graph. After that, I will find the closest neighbor to that starting point. Then we'll add the edge connecting those two points to the MST, and also add the vertices to the visited list for checking later, so that we won't form any loops in the graph. Here's the error that gets thrown: Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 0, Size: 0 at java.util.ArrayList.rangeCheck(Unknown Source) at java.util.ArrayList.get(Unknown Source) at Graph.findClosestNeighbour(graph.java:203) at Graph.Prim(graph.java:179) at MST.main(MST.java:49) Line 203: return neighbour.get(0); in findClosestNeighbour() Line 179: Edge e = findClosestNeighbour(startingVertex); in Prim()

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• How do you draw a line from one corner of the stage to the other?

  - by George Edison

  I am completely perplexed. I asked this question and it (any mentioned solution) doesn't seem to be working at all. All I want is to draw a line from one corner to the other. Here again is the link to the SWF file I have (it's embedded in an HTML document): test.html Here is the source: package { import flash.display.Sprite; import flash.events.Event; public class Main extends Sprite { public function Main():void { if (stage) init(); else addEventListener(Event.ADDED_TO_STAGE, init); } private function init(e:Event = null):void { removeEventListener(Event.ADDED_TO_STAGE, init); // entry point graphics.clear(); graphics.lineStyle(10, 0x000000); graphics.moveTo(0, 0); graphics.lineTo(stage.stageWidth, stage.stageHeight); } } } It just doesn't work! The line goes from somewhere offscreen to about the middle of the stage. What on earth am I doing wrong?

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• py.test import context problems (causes Django unit test failure)

  - by dhill

  I made a following test: # main.py import imported print imported.f.__module__ # imported.py def f(): pass # test_imported.py (py.test test case) import imported def test_imported(): result = imported.f.__module__ assert result == 'imported' Running python main.py, gives me imported, but running py.test gives me error and result value is moduletest.imported (moduletest is the name of the directory I keep the test in. It doesn't contain __init__.py, moduletest is the only directory containing *.py files in ~/tmp). How can I fix result value? The long story: I'm getting strange errors, while testing Django application. A call to reverse() from (django.urlresolvers). with function object foo as argument in tests crashes with NoReverseMatch: Reverse for 'site.app.views.foo'. The same call inside application works. I checked and it is converted to 'app.views.foo' (without site prefix). I first suspected my customised test setup for Django, but then I made above test.

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• Why isn't the static constructor of the parent class called when invoking a method on a nested class

  - by Ryan Ische

  Given the following code, why isn't the static constructor of "Outer" called after the first line of "Main"? namespace StaticTester { class Program { static void Main( string[] args ) { Outer.Inner.Go(); Console.WriteLine(); Outer.Go(); Console.ReadLine(); } } public static partial class Outer { static Outer() { Console.Write( "In Outer's static constructor\n" ); } public static void Go() { Console.Write( "Outer Go\n" ); } public static class Inner { static Inner() { Console.Write( "In Inner's static constructor\n" ); } public static void Go() { Console.Write( "Inner Go\n" ); } } } }

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• Loading Files in AppEngine

  - by Chris M

  I've got a tiny bit of code to display a file in app.yaml - url: /(.*\.(gif|png|jpg)) static_files: static/\1 upload: static/(.*\.(gif|png|jpg)) in main.py ... class ShowImage(webapp.RequestHandler): def get(self): rootpath = os.path.dirname(__file__) file = rootpath + "/static/tracker.gif"; fh=open(file, 'r') self.response.out.write(fh.read()) fh.close ... I can see the files gone up by going to my *.appspot.com/tracker.gif (as per the app.yaml) But using *.appspot.com/showimage returns Traceback (most recent call last): File "/base/python_lib/versions/1/google/appengine/ext/webapp/__init__.py", line 510, in __call__ handler.get(*groups) File "/base/data/home/apps/APPNAME/2.341131266814384624/main.py", line 170, in get fh=open(file, 'r') IOError: [Errno 2] No such file or directory: '/base/data/home/apps/APPNAME/2.341131266814384624/static/tracker.gif'

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• Running out of memory with UIImage creation on an offscreen Bitmap Context by NSOperation

  - by sigsegv

  I have an app with multiple UIView subclasses that acts as pages for a UIScrollView. UIViews are moved back and forth to provide a seamless experience to the user. Since the content of the views is rather slow to draw, it's rendered on a single shared CGBitmapContext guarded by locks by NSOperation subclasses - executed one at once in an NSOperationQueue - wrapped up in an UIImage and then used by the main thread to update the content of the views. -(void)main { NSAutoreleasePool * pool = [[NSAutoreleasePool alloc]init]; if([self isCancelled]) { return; } if(nil == data) { return; } // Buffer is the shared instance of a CG Bitmap Context wrapper class // data is a dictionary CGImageRef img = [buffer imageCreateWithData:data]; UIImage * image = [[UIImage alloc]initWithCGImage:img]; CGImageRelease(img); if([self isCancelled]) { [image release]; return; } NSDictionary * result = [[NSDictionary alloc]initWithObjectsAndKeys:image,@"image",id,@"id",nil]; // target is the instance of the UIView subclass that will use // the image [target performSelectorOnMainThread:@selector(updateContentWithData:) withObject:result waitUntilDone:NO]; [result release]; [image release]; [pool release]; } The updateContentWithData: of the UIView subclass performed on the main thread is just as simple -(void)updateContentWithData:(NSDictionary *)someData { NSDictionary * data = [someData retain]; if([[data valueForKey:@"id"]isEqualToString:[self pendingRequestId]]) { UIImage * image = [data valueForKey:@"image"]; [self setCurrentImage:image]; [self setNeedsDisplay]; } // If the image has not been retained, it should be released together // with the dictionary retaining it [data release]; } The drawLayer:inContext: method of the subclass will just get the CGImage from the UIImage and use it to update the backing layer or part of it. No retain or release is involved in the process. The problem is that after a while I run out of memory. The number of the UIViews is static. CGImageRef and UIImage are created, retained and released correctly (or so it seems to me). Instruments does not show any leaks, just the free memory available dip constantly, rise a few times, and then dip even lower until the application is terminated. The app cycles through about 2-300 of the aforementioned pages before that, but I would expect to have the memory usage reach a more or less stable level of used memory after a bunch of pages have been already skimmed at fast speed or, since the images are up to 3MB in size, deplete way earlier. Any suggestion will be greatly appreciated.

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• Java assert nasty side-effect - compiler bug?

  - by Alex

  This public class test { public static void main(String[] args) { Object o = null; assert o != null; if(o != null) System.out.println("o != null"); } } prints out "o != null"; both 1.5_22 and 1.6_18. Compiler bug? Commenting out the assert fixes it. The byte code appears to jump directly to the print statement when assertions are disabled: public static main(String[]) : void L0 LINENUMBER 5 L0 ACONST_NULL ASTORE 1 L1 LINENUMBER 6 L1 GETSTATIC test.$assertionsDisabled : boolean IFNE L2 ALOAD 1: o IFNONNULL L2 NEW AssertionError DUP INVOKESPECIAL AssertionError.<init>() : void ATHROW L2 LINENUMBER 8 L2 GETSTATIC System.out : PrintStream LDC "o != null" INVOKEVIRTUAL PrintStream.println(String) : void L3 LINENUMBER 9 L3 RETURN L4

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• problem in loading class from 'me.prettyprint.hector.api.Serializer'

  - by dhananjay patil

  I have created executable jar but having some problem with Class not found Exception. When I type command: java -jar JarFileName.jar arguments.. I get error message, Exception in thread "main" java.lang.NoClassDefFoundError: me/prettyprint/hector/api/Serializer at com.ensarm.niidle.web.scraper.NiidleScrapeManager.main(NiidleScrapeManager.java:21) Caused by: java.lang.ClassNotFoundException: me.prettyprint.hector.api.Serializer at java.net.URLClassLoader$1.run(URLClassLoader.java:200) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:188) at java.lang.ClassLoader.loadClass(ClassLoader.java:307) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301) at java.lang.ClassLoader.loadClass(ClassLoader.java:252) at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:320) ... 1 more please tell me solution for this,class is not getting loaded from the external jar

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• I have lots of images on a html page - how can i make certain ones load first (or certain ones load

  - by imlostmike

  Hi, i have a page with the main content area being big thumbnails, but elsewhere on the page are about 100-200 other (smaller) thumbs that are not important but must still show. What ways do i have to make the main ones show first (or the unimportant ones show last)? I was thinking of these ways: JS load: on page load (once it has finished loading), use a jquery's append() (or whatever other way) to write the html with the image code Set all unimportant images inside a div with style="display:none;". Then once the page has loaded, use JS to set it as visible what do you think is the best way?

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• Executing Secondary Applications

  - by JooBlow

  I have an application I am attempting to make "portable". The application contains a lot of secondary utility functions that I would like to execute on external files(from the app). I tried adding them in the build process but I didn't get any "Executables" for them(just the main one and a few others). Is there a way to get these to excute? They are basically command line utility functions to process some text files but use large files in the distribution and are also used by the main application. Thanks

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• MS Access 2003 - Option Group frame: can I add text boxes that are part of the frame instead of rad

  - by Justin

  Ok so this maybe a simple/silly question but I don't know so here goes: In access let's say I want to have a frame control, so I click the option group button and add it to the desgin surface. However, I am not wanting to use this as a option group with radio button selection, instead I would like to add text boxes instead the frame, so that when I reference the frame, it references every control instead of it, hence the text boxes, cbo boxes, etc.....just as it would if they were radio option selections. So can you do this? I want whatever controls I add inside the frame to be easily referenced (i.e. make all controls visible just by using frameExample.visible = true) so that I can build my own tab control groupings..... can this be done? Thanks! EDIT: What I am trying to accomplish is having a form that includes a collection of controls (input controls - cbo boxes, text boxes, etc), that serve as the Main record information. These are saved to a table via an INSERT statement on button_click because this form is unbound. Next I have 8 categories that are relative per each main record (and data that goes along with it). Each of these categories could have a sub form area and a button click that bring it's relative form into the sub form area. These sub forms would be unbound as well as I would just save data via SQL statement. So i know I could accomplish this by running the insert statement from the parent form, on the main collection control's data that would create the KeyID number, then run a SQL statement that would turn around and load that KeyID number right back onto the page in a hidden text box. Then when I click one of the sub forms and load its relative collection of controls, I could then save that data along with KeyID for each of these sub-forms/tables. SO...... I was wondering if instead you could define these controls as a collection so that you could hide and make visible all the ones you need on button clicks and avoid the need for additional forms (subs). I know that if a user enters data into a text box, and then somewhere along the way that box becomes hidden, the data still exists in it and still ends up in the SQL statement.... So I want all these controls to exist on the same form, but I thought what is I could encapsulate them into a frame like an option group, then I could call the frame and all the relative controls would be called up (made visible) as needed. Sorry for the long explanation but I thought it would help.

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• Building two executables in one project

  - by Rui Pacheco

  Hi, I've a project that must produce two executables: the main application and an executable that is called by a separate process. I've created the second file in Xcode and added a second target of type Cocoa Shell Tool. I can now build the second executable but when I try to build my project normally I get an error saying there's two executables present: ld: duplicate symbol _main in <path>/SecondExecutable.o and <path>/main.o (<path> was added by me to protect the innocent and their intelectual property). How can I configure Xcode to build both at the same time?

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• Multi-Threading - Cleanup strategy at program end

  - by weismat

  What is the best way to finish a multi-threaded application in a clean way? I am starting several socket connections from the main thread in seperate sockets and wait until the end of my business day in the main thread and use currently System.Environment.Exit(0) to terminate it. This leads to an unhandled execption in one of the childs. Should I stop the threads from the list? I have been reluctant to implement any real stopping in the childs yet, thus I am wondering about the best practice. The sockets are all wrapped nicely with proper destructors for logging out and closing, but it still leads to errors.

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• Visual Studio ReportViewer repeating data block on every page

  - by muhan

  I am using Reportviewer to generate a sales invoice to be printed by the user. How can I get databound fields to be printed on every page of a multi page invoice? The invoice is printed on a pre-printed form. I want the printed form to look roughly like: page 1 customer john smith 123 main st. city, CA 90000 some item1 $100 some item2 $150 some item3 $150 page 2 customer john smith 123 main st. city, CA 90000 some item4 $500 some item5 $250 some item6 $950 Total $2100 Using 1 list which contains databound textbox fields for the customer info, and a table for the items. The problem is if there are many items such that the items flow over to page 2, the next page only contains items, and not the customer info which needs to be printed on second page as well. I tried using page header, but I can't use databound items in page header. Please Help!

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• Invoke an Overloaded Constructor through this keyword (What's the Different between this two Sample code?)

  - by Alireza Dehqani

  using System; namespace ConsoleApplication1 { class Program { static void Main() { // Sample Sample ob = new Sample(); // line1 // Output for line1 /* * Sample(int i) * Sample() / // Sample2 Sample2 ob2 = new Sample2(); // line2 // Output for line2 / * Sample2() */ } } class Sample { // Fields private int a; // Constructors public Sample(int i) // Main Constructor { Console.WriteLine(" Sample(int i)"); a = i; } // Default Constructor public Sample() : this(0) { Console.WriteLine(" Sample()"); } } class Sample2 { // fields private int a; // Constructors public Sample2(int i) { Console.WriteLine("Sample2(int i)"); a = i; } public Sample2() { Console.WriteLine("Sample2()"); a = 0; } } }

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• Watching a variable for changes without polling.

  - by milkfilk

  I'm using a framework called Processing which is basically a Java applet. It has the ability to do key events because Applet can. You can also roll your own callbacks of sorts into the parent. I'm not doing that right now and maybe that's the solution. For now, I'm looking for a more POJO solution. So I wrote some examples to illustrate my question. Please ignore using key events on the command line (console). Certainly this would be a very clean solution but it's not possible on the command line and my actual app isn't a command line app. In fact, a key event would be a good solution for me but I'm trying to understand events and polling beyond just keyboard specific problems. Both these examples flip a boolean. When the boolean flips, I want to fire something once. I could wrap the boolean in an Object so if the Object changes, I could fire an event too. I just don't want to poll with an if() statement unnecessarily. import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; /* * Example of checking a variable for changes. * Uses dumb if() and polls continuously. */ public class NotAvoidingPolling { public static void main(String[] args) { boolean typedA = false; String input = ""; System.out.println("Type 'a' please."); while (true) { InputStreamReader isr = new InputStreamReader(System.in); BufferedReader br = new BufferedReader(isr); try { input = br.readLine(); } catch (IOException ioException) { System.out.println("IO Error."); System.exit(1); } // contrived state change logic if (input.equals("a")) { typedA = true; } else { typedA = false; } // problem: this is polling. if (typedA) System.out.println("Typed 'a'."); } } } Running this outputs: Type 'a' please. a Typed 'a'. On some forums people suggested using an Observer. And although this decouples the event handler from class being observed, I still have an if() on a forever loop. import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; import java.util.Observable; import java.util.Observer; /* * Example of checking a variable for changes. * This uses an observer to decouple the handler feedback * out of the main() but still is polling. */ public class ObserverStillPolling { boolean typedA = false; public static void main(String[] args) { // this ObserverStillPolling o = new ObserverStillPolling(); final MyEvent myEvent = new MyEvent(o); final MyHandler myHandler = new MyHandler(); myEvent.addObserver(myHandler); // subscribe // watch for event forever Thread thread = new Thread(myEvent); thread.start(); System.out.println("Type 'a' please."); String input = ""; while (true) { InputStreamReader isr = new InputStreamReader(System.in); BufferedReader br = new BufferedReader(isr); try { input = br.readLine(); } catch (IOException ioException) { System.out.println("IO Error."); System.exit(1); } // contrived state change logic // but it's decoupled now because there's no handler here. if (input.equals("a")) { o.typedA = true; } } } } class MyEvent extends Observable implements Runnable { // boolean typedA; ObserverStillPolling o; public MyEvent(ObserverStillPolling o) { this.o = o; } public void run() { // watch the main forever while (true) { // event fire if (this.o.typedA) { setChanged(); // in reality, you'd pass something more useful notifyObservers("You just typed 'a'."); // reset this.o.typedA = false; } } } } class MyHandler implements Observer { public void update(Observable obj, Object arg) { // handle event if (arg instanceof String) { System.out.println("We received:" + (String) arg); } } } Running this outputs: Type 'a' please. a We received:You just typed 'a'. I'd be ok if the if() was a NOOP on the CPU. But it's really comparing every pass. I see real CPU load. This is as bad as polling. I can maybe throttle it back with a sleep or compare the elapsed time since last update but this is not event driven. It's just less polling. So how can I do this smarter? How can I watch a POJO for changes without polling? In C# there seems to be something interesting called properties. I'm not a C# guy so maybe this isn't as magical as I think. private void SendPropertyChanging(string property) { if (this.PropertyChanging != null) { this.PropertyChanging(this, new PropertyChangingEventArgs(property)); } }

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• Using ret with FASM on Win32

  - by Jon Purdy

  I'm using SDL with FASM, and have code that's minimally like the following: format ELF extrn _SDL_Init extrn _SDL_SetVideoMode extrn _SDL_Quit extrn _exit SDL_INIT_VIDEO equ 0x00000020 section '.text' public _SDL_main _SDL_main: ccall _SDL_Init, SDL_INIT_VIDEO ccall _SDL_SetVideoMode, 640, 480, 32, 0 ccall _SDL_Quit ccall _exit, 0 ; Success, or ret ; failure. With the following quick-and-dirty makefile: SOURCES = main.asm OBJECTS = main.o TARGET = SDLASM.exe FASM = C:\fasm\fasm.exe release : $(OBJECTS) ld $(OBJECTS) -LC:/SDL/lib/ -lSDLmain -lSDL -LC:/MinGW/lib/ -lmingw32 -lcrtdll -o $(TARGET) --subsystem windows cleanrelease : del $(OBJECTS) %.o : %.asm $(FASM) $< $@ Using exit() (or Windows' ExitProcess()) seems to be the only way to get this program to exit cleanly, even though I feel like I should be able to use retn/retf. When I just ret without calling exit(), the application does not terminate and needs to be killed. Could anyone shed some light on this? It only happens when I make the call to SDL_SetVideoMode().

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