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• yet another question about migrating to Java

  - by aloneguid

  Hi, There are plenty similar questions, but maybe responses to this one will save a developer's life :) I want to migrate to Java. The reasons are very clear: all the .NET vacancies are client and windows oriented (Silverlight developer, ASP.NET developer, WPF developer etc.) and none of them are any interest to me. I worked with .NET since it's beginning as our company decided to invest in .NET having C++ stack and all the natual problems, so I was just blindly following and actually enjoyed it as the products were mostly server oriented with mixed C++/C# code. Today I have beforementioned problem - can't find an inspiring job. I'd rather kill myself than start working on a Silverlight or WPF project. Searching Java vacancies shows promising results, however they all require a huge java-related technology stack and experience. The question is is there any chance to find a job quickly and without dramatic salary drop (I know that Java guys are usually better paid, so there must be a kind of a credit) and if not, how must time and effort does it take to migrate (my .NET knowledge mostly includes server-oriented technologies like NHibernate, WCF, threading, sockets, ASP.NET web services, Enterprise Library, NInject etc etc etc, and (still) some C++ leftovers). Thanks!

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• How would you design a question/answer view (iPhone SDK)

  - by Aurélien Vallée

  I'm new to iPhone development, and I have a question on how to create a view for my application. The view should display a problem (using formatted/syntax highlighted text), and multiple possible answers. The user should be able to click on an answer to validate it. Currently, I am trying to use a UITableView embedding UIWebView as contentView. That allows me to display formatted text easily. The problem is that it is a real pain to compute and adjust the height of the cells. I have to preload the webview, call sizeToFit, get its height, and update the cell accordingly. This process should be done for the problem and the answers (as they are HTML formatted text too). It's such a pain that I am planning to switch to something else. I thought using only a big UIWebView and design everything in HTML. But I looked at some articles describing how to communicate between the HTML page and the ObjectiveC code. This seems to involve some awful tricks too... So... that's it, I don't really know what I should do. I guess some of you dealt with such things before, and would provide some greatly appreciated tips :)

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• Yet Another crosdomain.xml question or: "How to interpret documentation correctly"

  - by cboese

  Hi! I have read a lot about the new policy-policy of flash player and also know the master policy file. Now image the following situation: There are two servers with services (http) running at custom ports servera.com:2222/websiteA serverb.com:3333/websiteB Now I open a swf from server a (eg. servera.com:2222/websiteA/A.swf) that wants to access the service of serverb. Of course I need a crossdomain.xml at the right place and there are multiple variations possible. I dont want to use a master policy file, as I might not have control over the root of both servers. One solution I found works with the following crossdomain: <?xml version="1.0"?> <cross-domain-policy> <allow-access-from domain="*"/> </cross-domain-policy> served at serverb.com:3333/websiteB/crossdomain.xml So now for my question: Is it possible to get rid of the "*" and use a proper (not as general as *) domainname in the allow-access-from rule? All my attempts failed, and from what I understand it should be possible.

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• c# scope/typing/assignment question

  - by Shannow

  Hi there another quick question. I would like to create a variable object so that depending on the value of something, it gets cast as needed. e.g. var rule; switch (seqRuleObj.RuleType) { case SeqRuleObj.type.Pre : rule = new preConditionRuleType(); rule = (preConditionRuleType)seqRuleObj.Rule; break; case SeqRuleObj.type.Post : rule = new postConditionRuleType(); rule = (postConditionRuleType)seqRuleObj.Rule; break; case SeqRuleObj.type.Exit : rule = new exitConditionRuleType(); rule = (exitConditionRuleType)seqRuleObj.Rule; break; default : break; } String result; foreach (sequencingRuleTypeRuleConditionsRuleCondition cond in rule.ruleConditions.ruleCondition) { ....../ blah } so basically this will not work. c# will not allow me to create an new object in every case as the name is aleady defined. i can just paste the foreach loop into each case but that to me is such a waste, as the objects are exactly the same in all but name.

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• question regarding templatization of virtual function

  - by jan

  Hi, I am new to this forum and sorry If I am repeating this question. I know that you cannot templatize the virtual function and I do understand the concept behind it. But I still need a way to get across some errors I am getting it. I am able to make my stuff work but it doesn't look to me. Here's the deal, I have class called System, #include "Vector.h" class System { virtual void VectorToLocal(Vector<T>& global_dir,const Vector<T>* global_pos = 0) const = 0; }; class UnresolvedSystem : public System { virtual void VectorToLocal(Vector<T>& global_dir,const Vector<T>* global_pos = 0) const { //do something } }; In Vector.h tenplate<typename T> class Vector { //some functions }; See now I want to templatize VectorToLocal in system.h to take just Vector, but I cannot do it as it is a virtual function. I want a work around. I know I can have VectorToLocal take Vector, Vector etc as arguments. But I do not want to do it. Any help would be really appreciated. Thanks in advance, Jan

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• Autocomplete Error Question - Ruby on Rails

  - by bgadoci

  I have built a very simple blog application using Ruby on Rails. New to both Ruby and Rails so excuse the stupid questions. I currently have two tables that relate to this question. I have a Post table and a Tag table. Basically I set it up such that Post has_many :tags and Tag belongs_to :post. I am using AJAX to process and display the tags in the show view of the post. I installed the auto_complete plugin and I am getting an error when I enter the letters in the text_field_with_auto_complete for tag creation. My suspicion is this is because the form is a remote_form_for or something I am doing wrong in the routes.rb. Here is the error and code: Error Processing PostsController#show (for 127.0.0.1 at 2010-04-13 23:25:46) [GET] Parameters: {"tag"=>{"tag_name"=>"f"}, "id"=>"auto_complete_for_tag_tag_name"} Post Load (0.1ms) SELECT * FROM "posts" WHERE ("posts"."id" = 0) ActiveRecord::RecordNotFound (Couldn't find Post with ID=auto_complete_for_tag_tag_name): app/controllers/posts_controller.rb:22:in `show' Rendered rescues/_trace (26.0ms) Rendered rescues/_request_and_response (0.2ms) Rendering rescues/layout (not_found) remote_form_for located in /views/posts/show.html.erb <% remote_form_for [@post, Tag.new] do |f| %> <p> <%= f.label :tag_name, "Tag" %><br/> <%= text_field_with_auto_complete :tag, :tag_name, {}, {:method => :get} %> </p> <p><%= f.submit "Add Comment" %></p> <% end %> tags_controller.rb (I'll spare you all the actions but added the following here) auto_complete_for :tag, :tag_name routes.rb map.resources :posts, :has_many => :comments map.resources :posts, :has_many => :tags map.resources :tags, :collection => {:auto_complete_for_tag_tag_name => :get }

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• question/problem regarding assigning an array of char *

  - by Fantastic Fourier

  Hi I'm working with C and I have a question about assigning pointers. struct foo { int _bar; char * _car[MAXINT]; // this is meant to be an array of char * so that it can hold pointers to names of cars } int foofunc (void * arg) { int bar; char * car[MAXINT]; struct foo thing = (struct foo *) arg; bar = arg->_bar; // this works fine car = arg->_car; // this gives compiler errors of incompatible types in assignment } car and _car have same declaration so why am I getting an error about incompatible types? My guess is that it has something to do with them being pointers (because they are pointers to arrays of char *, right?) but I don't see why that is a problem. when i declared char * car; instead of char * car[MAXINT]; it compiles fine. but I don't see how that would be useful to me later when I need to access certain info using index, it would be very annoying to access that info later. in fact, I'm not even sure if I am going about the right way, maybe there is a better way to store a bunch of strings instead of using array of char *?

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• code igniter codeigniter question, making anchor load page containing data from referenced row in DB

  - by thrice801

  Hi, Im trying to learn the code igniter library and object oriented php in general and have a question. Ok so Ive gotten as far as making a page which loads all of the rows from my database and in there, Im echoing an anchor tag which is a link to the following structure. [code]echo anchor("videos/video/$row-video_id", $row-video_title);[/code] So, I have a class called Videos which extends the controller, within that class there is index and video, which is being called correctly (when you click on the video title, it sends you to videos/video/5 for example, 5 being the primary key of the table im working with. So basically all Im trying to do is pass that 5 back to the controller, and then have the particular video page output the particular rows data from the videos table. My function in my controller for video looks like this - [code] function video() { $data['main_content'] = 'video'; $data['video_title'] = 'test'; $this-load-view('includes/template', $data); } [/code] So ya, basically test should be instead of test, a returned value of a query which says get in the table "videos", the row with the video_id of "5", and make $data['video_title'] = value of video_title in database... Should have this figured out by now but dont, any help would be appreciated!

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• Noob question about a statement in a Java program

  - by happysoul

  I am beginner to java and was trying out this code puzzle from the book head first java which I solved as follows and got the output correct :D class DrumKit { boolean topHat=true; boolean snare=true; void playSnare() { System.out.println("bang bang ba-bang"); } void playTopHat() { System.out.println("ding ding da-ding"); } } public class DrumKitTestDriver { public static void main(String[] args) { DrumKit d =new DrumKit(); if(d.snare==true) { d.playSnare(); } d.playTopHat(); } } Output is :: bang bang ba-bang ding ding da-ding Now the problem is that in that code puzzle one code snippet is left that I did not include..it's as follows d.snare=false; Even though I did not write it , I got the output like the book. I am wondering why is there need for us to set it's value as false even when we know the code is gonna run without it too !?? I am wondering what the coder had in mind ..I mean what could be the possible future use and motive behind doing this ? I am sorry if it's a dumb question. I just wanna know why or why not to include that particular statement ? It's not like there's a loop or something that we need to come out of. Why is that statement there ?

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• Question concerning SCJP-6 exam

  - by abatishchev

  While preparing for the SCJP-6 exam I faced with a difficult issue. I can’t find answer by myself. Please, answer for the question and give short comments: abstract class A<K> extends Number> { // insert code here } public abstract <K> A<? extends Number> useMe(A<? super K> k); public abstract <K> A<? super Number> useMe(A<? extends K> k); public abstract <K> A<K> useMe(A<K> k); public abstract <V extends K> A<V> useMe(A<V> k); public abstract <V super K> A<V> useMe(A<V> k); public abstract <V extends Character> A<? super V> useMe(A<K> k); public abstract <V super Character> A<? super V> useMe(A<K> k); Which method can be inserted in a placeholder above? P.S. I tried to look on the specification. Those one was not helpful for me.

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• Another C question

  - by maddy

  Hi all, I have a piece of code shown below #include <stdio.h> #include <stdlib.h> void Advance_String(char [2],int ); int Atoi_val; int Count22; int Is_Milestone(char [2],int P2); char String[2] = "00"; main() { while(1) { if(Is_Milestone(S,21==1) { if(atoi(S)==22) { Count_22 = Count_22 + 1; } } Atoi_val = atoi(S); Advance_String(S,Atoi_val); } } int Is_Milestone(char P1[2],int P2) { int BoolInit; char *Ptr = P1; int value = atoi(Ptr); BoolInit = (value > P2); return BoolInit; } void Advance_String(char P1[2],int Value) { if(Value!=7) { P1[1] = P1[1]+1; } else { P1[1] = '0'; P1[0] = P1[0]+1 ; } } Now my problem is Count22 never increments as the char increments never achieves the value 21 or above.Could anyone please tell me the reason for this unexpected behaviour?My question here is to find the value of Count22.Is there any problem with the code? Thanks and regards Maddy

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• SQL Concurrent test update question

  - by ptoinson

  Howdy Folks, I have a SQLServer 2008 database in which I have a table for Tags. A tag is just an id and a name. The definition of the tags table looks like: CREATE TABLE [dbo].[Tag]( [ID] [int] IDENTITY(1,1) NOT NULL, [Name] [varchar](255) NOT NULL CONSTRAINT [PK_Tag] PRIMARY KEY CLUSTERED ( [ID] ASC )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ) Name is also a unique index. further I have several processes adding data to this table at a pretty rapid rate. These processes use a stored proc that looks like: ALTER PROC [dbo].[lg_Tag_Insert] @Name varchar(255) AS DECLARE @ID int SET @ID = (select ID from Tag where Name=@Name ) if @ID is null begin INSERT Tag(Name) VALUES (@Name) RETURN SCOPE_IDENTITY() end else begin return @ID end My issues is that, other than being a novice at concurrent database design, there seems to be a race condition that is causing me to occasionally get an error that I'm trying to enter duplicate keys (Name) into the DB. The error is: Cannot insert duplicate key row in object 'dbo.Tag' with unique index 'IX_Tag_Name'. This makes sense, I'm just not sure how to fix this. If it where code I would know how to lock the right areas. SQLServer is quite a different beast. First question is what is the proper way to code this 'check, then update pattern'? It seems I need to get an exclusive lock on the row during the check, rather than a shared lock, but it's not clear to me the best way to do that. Any help in the right direction will be greatly appreciated. Thanks in advance.

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• OOP 101 - quick question.

  - by R Bennett

  I've used procedural for sometime now and trying to get a better understanding of OOP in Php. Starting at square 1 and I have a quick question ot get this to gel. Many of the basic examples show static values ( $bob-name = "Robert";) when assigning a value, but I want to pass values... say from a form ( $name = $_POST['name']; ) class Person { // define properties public $name; public $weight; public $age; public function title() { echo $this->name . " has submitted a request "; } } $bob = new Person; // want to plug the value in here $bob->name = $name; $bob->title(); I guess I'm getting a little hung up in some areas as far as accessing variables from within the class, encapsulation & "rules", etc., can $name = $_POST['name']; reside anywhere outside of the class or am I missing an important point? Thanks

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• Important question about linq to SQL performance on high loaded web applications

  - by Alex

  I started working with linq to SQL several weeks ago. I got really tired of working with SQL server directly through the SQL queries (sqldatareader, sqlcommand and all this good stuff).  After hearing about linq to SQL and mvc I quickly moved all my projects to these technologies. I expected linq to SQL work slower but it suprisongly turned out to be pretty fast, primarily because I always forgot to close my connections when using datareaders. Now I don't have to worry about it. But there's one problem that really bothers me. There's one page that's requested thousands of times a day. The system gets data in the beginning, works with it and updates it. Primarily the updates are ++ @ -- (increase and decrease values). I used to do it like this UPDATE table SET value=value+1 WHERE ID=@I'd It worked with no problems obviously. But with linq to SQL the data is taken in the beginning, moved to the class, changed and then saved. Stats.registeredusers++; Db.submitchanges(); Let's say there were 100 000 users. Linq will say "let it be 100 001" instead of "let it be increased by 1". But if there value of users has already been increased (that happens in my site all the time) then linq will be like oops, this value is already 100 001. Whatever I'll throw an exception" You can change this behavior so that it won't throw an exception but it still will not set the value to 100 002. Like I said, it happened with me all the time. The stas value was increased twice a second on average. I simply had to rewrite this chunk of code with classic ado net. So my question is how can you solve the problem with linq

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• vb.net documentation and exception question

  - by dcp

  Let's say I have this sub in vb.net: ''' <summary> ''' Validates that <paramref name="value"/> is not <c>null</c>. ''' </summary> ''' ''' <param name="value">The object to validate.</param> ''' ''' <param name="name">The variable name of the object.</param> ''' ''' <exception cref="ArgumentNullException">If <paramref name="value"/> is <c>null</c>.</exception> Sub ValidateNotNull(ByVal value As Object, ByVal name As String) If value Is Nothing Then Throw New ArgumentNullException(name, String.Format("{0} cannot be null.", name)) End If End Sub My question is, is it proper to call this ValidateNotNull (which is what I would call it in C#) or should I stick with VB terminology and call it ValidateNotNothing instead? Also, in my exception, is it proper to say "cannot be null", or would it be better to say "cannot be Nothing"? I sort of like the way I have it, but since this is VB, maybe I should use Nothing. But since the exception itself is called ArgumentNullException, it feels weird to make the message say "cannot be Nothing". Anyway, I guess it's pretty nitkpicky, just wondered what you folks thought.

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• Question on boost array initializer

  - by ArunSaha

  I am trying to understand the boost array. The code can be read easily from author's site. In the design rationale, author (Nicolai M. Josuttis) mentioned that the following two types of initialization is possible. boost::array<int,4> a = { { 1, 2, 3 } }; // Line 1 boost::array<int,4> a = { 1, 2, 3 }; // Line 2 In my experiment with g++ (version 4.1.2) Line 1 is working but Line 2 is not. (Line 2 yields the following: warning: missing braces around initializer for 'int [4]' warning: missing initializer for member 'boost::array<int, 4ul>::elems' ) Nevertheless, my main question is, how Line 1 is working? I tried to write a class similar to array.hpp and use statement like Line 1, but that did not work :-(. Can somebody explain me? Is there some boost specific thing happening in Line 1 that I need to be aware of? Thanks in advance. Regards,

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• Question about making Asynchronous call in C# (WPF) to COM object

  - by Andrew

  Hi, Sorry to ask such a basic question but I seem to have a brain freeze on this one! I'm calling a COM (ATL) object from my WPF project. The COM method might take a long time to complete. I thought I'd try and call it asychronously. I have a few demo lines that show the problem. private void checkBox1_Checked(object sender, RoutedEventArgs e) { //DoSomeWork(); AsyncDoWork caller = new AsyncDoWork(DoSomeWork); IAsyncResult result = caller.BeginInvoke(null, null); } private delegate void AsyncDoWork(); private void DoSomeWork() { _Server.DoWork(); } The ATL method DoWork is very exciting. It is: STDMETHODIMP CSimpleObject::DoWork(void) { Sleep(5000); return S_OK; } I had expectations that running this way would result in the checkbox being checked right away (instead of in 5 seconds) and me being able to move the WPF gui around the screen. I can't - for 5 seconds. What am I doing wrong? I'm sure it's something pretty simple. Delegate signature wrong? Thanks.

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• JSON VIEW using GROUP_CONCAT question

  - by Dan Beam

  Hey DBAs and overall smart dudes. I have a question for you. We use MySQL VIEWs to format our data as JSON when it's returned (as a BLOB), which is convenient (though not particularly nice on performance, but we already know this). But, I can't seem to get a particular query working right now (each row contains NULL when it should contain a created JSON object with the values of multiple JOINs). Here's the general idea: SELECT CONCAT( "{", "\"some_list\":[", GROUP_CONCAT( DISTINCT t1.id ), "],", "\"other_list\":[", GROUP_CONCAT( DISTINCT t2.id ), "],", "}" ) cool_json FROM table_name tn INNER JOIN ( some_table st ) ON st.some_id = tn.id LEFT JOIN ( another_table at, another_one ao, used_multiple_times t1 ) ON st.id = at.some_id AND at.different_id = ao.different_id AND ao.different_id = t1.id LEFT JOIN ( another_table2 at2, another_one2 ao2, used_multiple_times t2 ) ON st.id = at2.some_id AND at2.different_id = ao2.different_id AND ao2.different_id = t2.id GROUP BY tn.id ORDER BY tn.name Anybody know the problem here? Am I missing something I should be grouping by? It was working when I was only doing 1 LEFT JOIN & GROUP_CONCAT, but now with multiple JOINs / GROUP_CONCATs it's messing it up. When I move the GROUP_CONCATs from the "cool_json" field they work as expected, but I'd like my data formatted as JSON so I can decode it server-side or client-side in one step.

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• conceptual question : what do performSelectorOnMainThread do?

  - by hib

  Hello all, I just come across this strange situation . I was using the technique of lazy image loading from apple examples . when I was used the class in my application it gave me topic to learn but don't what was actually happening there . So here goes the scenario : I think everybody has seen the apple lazytableimagesloading . I was reloading my table on finishing the parsing of data : - (void)didFinishParsing:(NSMutableArray *)appList { self.upcomingArray = [NSMutableArray arrayWithArray:loadedApps]; // we are finished with the queue and our ParseOperation [self.upcomingTableView reloadData]; self.queue = nil; // we are finished with the queue and our ParseOperation } but as a result the the connection was not starting and images were not loading . when I completely copy the lazyimageloading and I replaced the above code with the following code it works fine - (void)didFinishParsing:(NSMutableArray *)appList { [self performSelectorOnMainThread:@selector(handleLoadedApps:) withObject:appList waitUntilDone:NO]; self.queue = nil; // we are finished with the queue and our ParseOperation } So I want to know what is the concept behind this . Please let me know if you can not understand the question or details are not enough because I desperately want to know why it is like this ?

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• mysql and trigger usage question

  - by dhruvbird

  I have a situation in which I don't want inserts to take place (the transaction should rollback) if a certain condition is met. I could write this logic in the application code, but say for some reason, it has to be written in MySQL itself (say clients written in different languages will be inserting into this MySQL InnoDB table) [that's a separate discussion]. Table definition: CREATE TABLE table1(x int NOT NULL); The trigger looks something like this: CREATE TRIGGER t1 BEFORE INSERT ON table1 FOR EACH ROW IF (condition) THEN NEW.x = NULL; END IF; END; I am guessing it could also be written as(untested): CREATE TRIGGER t1 BEFORE INSERT ON table1 FOR EACH ROW IF (condition) THEN ROLLBACK; END IF; END; But, this doesn't work: CREATE TRIGGER t1 BEFORE INSERT ON table1 ROLLBACK; You are guaranteed that: Your DB will always be MySQL Table type will always be InnoDB That NOT NULL column will always stay the way it is Question: Do you see anything objectionable in the 1st method?

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• a question related to URL

  - by Robert

  Dear all,Now i have this question in my java program,I think it should be classified as URL problem,but not 100% sure.If you think I am wrong,feel free to recategorize this problem,thanks. I would state my problem as simply as possible. I did a search on the famouse Chinese search engine baidu.com for a Chinese key word "???" (Obama in English),and the way I do that is to pass a URL (in a Java Program)to the browser like: http://news.baidu.com/ns?word=??? and it works perfectly just like I input the "???”keyword in the text field on baidu.com. However,now my advisor wants another thing.Since he can not read the Chinese webpages,but he wants to make sure the webpages I got from Baidu.com is related to "Obama",he asked me to google translate it back,i.e,using google translate and translate the Chinese webpage to English one. This sounds straightforward.However,I met my problem here. If I simply pass the URL "http://news.baidu.com/ns?word=???" into Google Translate and tick "Chinese to English" translating option,the result looks awful.(I don't know the clue here,maybe related to Chinese character encoding). Alternatively,if now my browser opens ""http://news.baidu.com/ns?word=???" webpage,but I click on the "????" button (that simply means "search"),you will notice the URL will get changed,now if I pass this URL into the Google translate and do the same thing,the result works much better. I hope I am not making this problem sound too complicated,and I appologize for some Chinese words invovled,but I really need your guys' help here.Becasue I did all this in a Java program,I couldn't figure out how to realize that "????"(pressing search button) step then get the new URL.If I could get that new URL,things are easy,I could just call Google translate in my Java code,and pops out the new window to show my advisor. Please share any of your idea or thougts here.Thanks a lot. Robert

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• Java Concurrency in practice sample question

  - by andy boot

  I am reading "Java Concurrency in practice" and looking at the example code on page 51. According to the book this piece of code is at risk of of failure if it has not been published properly. Because I like to code examples and break them to prove how they work. I have tried to make it throw an AssertionError but have failed. (Leading me to my previous question) Can anyone post sample code so that an AssertionError is thrown? Rule: Do not modify the Holder class. public class Holder{ private int n; public Holder(int n){ this.n = n; } public void assertSanity(){ if (n != n) { throw new AssertionError("This statement is false"); } } } I have modified the class to make it more fragile but I still can not get an AssertionError thrown. class Holder2{ private int n; private int n2; public Holder2(int n) throws InterruptedException{ this.n = n; Thread.sleep(200); this.n2 = n; } public void assertSanity(){ if (n != n2) { throw new AssertionError("This statement is false"); } } } Is it possible to make either of the above classes throw an AssertionError? Or do we have to accept that they may occasionally do so and we can't write code to prove it?

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• Newbie question: When to use extern "C" { //code } ?

  - by Russel

  Hello, Maybe I'm not understanding the differences between C and C++, but when and why do we need to use: extern "C" { ? Apparently its a "linkage convention"? I read about it briefly and noticed that all the .h header files included with MSVS surround their code with it. What type of code exactly is "C code" and NOT "C++ code"? I thought C++ included all C code? I'm guessing that this is not the case and that C++ is different and that standard features/functions exist in one or the other but not both (ie: printf is C and cout is C++), but that C++ is backwards compatible though the extern "C" declaration. Is this correct? My next question depends on the answer to the first, but I'll ask it here anyway: Since MSVS header files that are written in C are surrounded by extern "C" { ... }, when would you ever need to use this yourself in your own code? If your code is C code and you are trying to compile it in a C++ compiler, shouldn't it work without problem because all the standard h files you include will already have the extern "C" thing in them with the C++ compiler? Do you have to use this when compiling in C++ but linking to alteady built C libraries or something? Please help clarify this for me... Thanks! --Keith

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• Implementation/interface inheritance design question.

  - by Neil G

  I would like to get the stackoverflow community's opinion on the following three design patterns. The first is implementation inheritance; the second is interface inheritance; the third is a middle ground. My specific question is: Which is best? implementation inheritance: class Base { X x() const = 0; void UpdateX(A a) { y_ = g(a); } Y y_; } class Derived: Base { X x() const { return f(y_); } } interface inheritance: class Base { X x() const = 0; void UpdateX(A a) = 0; } class Derived: Base { X x() const { return x_; } void UpdateX(A a) { x_ = f(g(a)); } X x_; } middle ground: class Base { X x() const { return x_; } void UpdateX(A a) = 0; X x_; } class Derived: Base { void UpdateX(A a) { x_ = f(g(a)); } } I know that many people prefer interface inheritance to implementation inheritance. However, the advantage of the latter is that with a pointer to Base, x() can be inlined and the address of x_ can be statically calculated.

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• Question about compilers and how they work

  - by Marin Doric

  This is the C code that frees memory of a singly linked list. It is compiled with Visual C++ 2008 and code works as it should be. /* Program done, so free allocated memory */ current = head; struct film * temp; temp = current; while (current != NULL) { temp = current->next; free(current); current = temp; } But I also encountered ( even in a books ) same code written like this: /* Program done, so free allocated memory */ current = head; while (current != NULL) { free(current); current = current->next; } If I compile that code with my VC++ 2008, program crashes because I am first freeing current and then assigning current-next to current. But obviously if I compile this code with some other complier ( for example, compiler that book author used ) program will work. So question is, why does this code compiled with specific compiler work? Is it because that compiler put instructions in binary file that remember address of current-next although I freed current and my VC++ doesn't. I just want to understand how compilers work.

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