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• Why doesn't java.lang.Number implement Comparable?

  - by Julien Chastang

  Does anyone know why java.lang.Number does not implement Comparable? This means that you cannot sort Numbers with Collections.sort which seems to me a little strange. Post discussion update: Thanks for all the helpful responses. I ended up doing some more research about this topic. The simplest explanation for why java.lang.Number does not implement Comparable is rooted in mutability concerns. For a bit of review, java.lang.Number is the abstract super-type of AtomicInteger, AtomicLong, BigDecimal, BigInteger, Byte, Double, Float, Integer, Long and Short. On that list, AtomicInteger and AtomicLong to do not implement Comparable. Digging around, I discovered that it is not a good practice to implement Comparable on mutable types because the objects can change during or after comparison rendering the result of the comparison useless. Both AtomicLong and AtomicInteger are mutable. The API designers had the forethought to not have Number implement Comparable because it would have constrained implementation of future subtypes. Indeed, AtomicLong and AtomicInteger were added in Java 1.5 long after java.lang.Number was initially implemented. Apart from mutability, there are probably other considerations here too. A compareTo implementation in Number would have to promote all numeric values to BigDecimal because it is capable of accommodating all the Number sub-types. The implication of that promotion in terms of mathematics and performance is a bit unclear to me, but my intuition finds that solution kludgy.

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• Entity Framework DateTime update extremely slow

  - by Phyxion

  I have this situation currently with Entity Framework: using (TestEntities dataContext = DataContext) { UserSession session = dataContext.UserSessions.FirstOrDefault(userSession => userSession.Id == SessionId); if (session != null) { session.LastAvailableDate = DateTime.Now; dataContext.SaveChanges(); } } This is all working perfect, except for the fact that it is terribly slow compared to what I expect (14 calls per second, tested with 100 iterations). When I update this record manually through this command: dataContext.Database.ExecuteSqlCommand(String.Format("update UserSession set LastAvailableDate = '{0}' where Id = '{1}'", DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss.fffffff"), SessionId)); I get 55 calls per second, which is more than fast enough. However, when I don't update the session.LastAvailableDate but I update an integer (e.g. session.UserId) or string with Entity Framework, I get 50 calls per second, which is also more than fast enough. Only the datetime field is terrible slow. The difference of a factor 4 is unacceptable and I was wondering how I can improve this as I don't prefer using direct SQL when I can also use the Entity Framework. I'm using Entity Framework 4.3.1 (also tried 4.1).

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• Error in bisection method code in Matlab

  - by Amanda Collins

  I need to write a proper implementation of the bisection method, which means I must address all possible user input errors. Here is my code: function [x_sol, f_at_x_sol, N_iterations] = bisection(f, xn, xp, eps_f, eps_x) % solving f(x)=0 with bisection method % f is the function handle to the desired function, % xn and xp are borders of search, % f(xn)<0 and f(xp)>0 required, % eps_f defines how close f(x) should be to zero, % eps_x defines uncertainty of solution x if(f(xp) < 0) error('xp must be positive') end; if(f(xn)>0) error('xn must be negative') end; if (xn >= xp) error ('xn must be less than xp') end; xg=(xp+xn)/2; %initial guess fg=f(xg); % initial function evaluation N_iterations=1; while ( (abs(fg) > eps_f) & (abs(xg-xp) > eps_x) ) if (fg>0) xp=xg; else xn=xg; end xg=(xp+xn)/2; %update guess fg=f(xg); %update function evaluation N_iterations=N_iterations+1; end x_sol=xg; %solution is ready f_at_x_sol=fg; if (f_at_x_sol > eps_f) error('No convergence') end and here is the error message I receive when I try to test this in Matlab: >> bisection(x.^2, 2, -1, 1e-8, 1e-10) Attempted to access f(-1); index must be a positive integer or logical. Error in bisection (line 9) if(f(xp)<0) I was attempting to see if my error codes worked, but it doesn't look like they do. I get the same error when I try to test it on a function that should work.

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• Java: ResultSet exception - before start of result set

  - by Rosarch

  I'm having trouble getting data from a ResultSet object. Here is my code: String sql = "SELECT type FROM node WHERE nid = ?"; PreparedStatement prep = conn.prepareStatement(sql); int meetNID = Integer.parseInt(node.get(BoutField.field_meet_nid)); prep.setInt(1, meetNID); ResultSet result = prep.executeQuery(); result.beforeFirst(); String foundType = result.getString(1); if (! foundType.equals("meet")) { throw new IllegalArgumentException(String.format("Node %d must be of type 'meet', but was %s", meetNID, foundType)); } The error trace: Exception in thread "main" java.sql.SQLException: Before start of result set at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1072) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:986) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:981) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:926) at com.mysql.jdbc.ResultSetImpl.checkRowPos(ResultSetImpl.java:841) at com.mysql.jdbc.ResultSetImpl.getStringInternal(ResultSetImpl.java:5656) at com.mysql.jdbc.ResultSetImpl.getString(ResultSetImpl.java:5576) at nth.cumf3.nodeImport.Validator.validate(Validator.java:43) at nth.cumf3.nodeImport.Main.main(Main.java:38) What am I doing wrong here?

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• Best practices for encrypting continuous/small UDP data

  - by temp

  Hello everyone, I am having an application where I have to send several small data per second through the network using UDP. The application need to send the data in real-time (no waiting). I want to encrypt these data and insure that what I am doing is as secure as possible. Since I am using UDP, there is no way to use SSL/TLS, so I have to encrypt each packet alone since the protocol is connectionless/unreliable/unregulated. Right now, I am using a 128-bit key derived from a passphrase from the user, and AES in CBC mode (PBE using AES-CBC). I decided to use a random salt with the passphrase to derive the 128-bit key (prevent dictionary attack on the passphrase), and of course use IVs (to prevent statistical analysis for packets). However I am concerned about few things: Each packet contains small amount of data (like a couple of integer values per packet) which will make the encrypted packets vulnerable to known-plaintext attacks (which will result in making it easier to crack the key). Also, since the encryption key is derived from a passphrase, this will make the key space way less (I know the salt will help, but I have to send the salt through the network once and anyone can get it). Given these two things, anyone can sniff and store the sent data, and try to crack the key. Although this process might take some time, once the key is cracked all the stored data will be decrypted, which will be a real problem for my application. So my question is, what is the best practices for sending/encrypting continuous small data using a connectionless protocol (UDP)? Is my way the best way to do it? ...flowed? ...Overkill? ... Please note that I am not asking for a 100% secure solution, as there is no such thing. Cheers

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• How to deal with a flaw in System.Data.DataTableExtensions.CopyToDataTable()

  - by andy

  Hey guys, so I've come across something which is perhaps a flaw in the Extension method .CopyToDataTable. This method is used by Importing (in VB.NET) System.Data.DataTableExtensions and then calling the method against an IEnumerable. You would do this if you want to filter a Datatable using LINQ, and then restore the DataTable at the end. i.e: Imports System.Data.DataRowExtensions Imports System.Data.DataTableExtensions Public Class SomeClass Private Shared Function GetData() As DataTable Dim Data As DataTable Data = LegacyADO.NETDBCall Data = Data.AsEnumerable.Where(Function(dr) dr.Field(Of Integer)("SomeField") = 5).CopyToDataTable() Return Data End Function End Class In the example above, the "WHERE" filtering might return no results. If this happens CopyToDataTable throws an exception because there are no DataRows. Why? The correct behavior should be to return a DataTable with Rows.Count = 0. Can anyone think of a clean workaround to this, in such a way that whoever calls CopyToDataTable doesn't have to be aware of this issue? System.Data.DataTableExtensions is a Static Class so I can't override the behavior....any ideas? Have I missed something? cheers UPDATE: I have submitted this as an issue to Connect. I would still like some suggestions, but if you agree with me, you could vote up the issue at Connect via the link above cheers

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• create and write to a text file in vb.net

  - by woolardz

  I'm creating a small vb.net application, and I'm trying trying to write a list of results from a listview to a text file. I've looked online and found the code to open the save file dialog and write the text file. When I click save on the save file dialog, I receive an IOException with the message "The process cannot access the file 'C:\thethe.txt' because it is being used by another process." The text file is created in the correct location, but is empty. The application quits at this line "Dim fs As New FileStream(saveFileDialog1.FileName, FileMode.OpenOrCreate, FileAccess.Write)" Thanks in advance for any help. Private Sub btnSave_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnSave.Click Dim myStream As Stream Dim saveFileDialog1 As New SaveFileDialog() saveFileDialog1.Filter = "txt files (*.txt)|*.txt|All files (*.*)|*.*" saveFileDialog1.FilterIndex = 2 saveFileDialog1.RestoreDirectory = True If saveFileDialog1.ShowDialog() = DialogResult.OK Then myStream = saveFileDialog1.OpenFile() If (myStream IsNot Nothing) Then Dim fs As New FileStream(saveFileDialog1.FileName, FileMode.OpenOrCreate, FileAccess.Write) Dim m_streamWriter As New StreamWriter(fs) m_streamWriter.Flush() 'Write to the file using StreamWriter class m_streamWriter.BaseStream.Seek(0, SeekOrigin.Begin) 'write each row of the ListView out to a tab-delimited line in a file For i As Integer = 0 To Me.ListView1.Items.Count - 1 m_streamWriter.WriteLine(((ListView1.Items(i).Text & vbTab) + ListView1.Items(i).SubItems(0).ToString() & vbTab) + ListView1.Items(i).SubItems(1).ToString()) Next myStream.Close() End If End If End Sub

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• ANDROID IF/ELSE FAILS CONTINUES TO EXECUTE JSON

  - by Keith Cesar Haizlett

  I am trying to create a Registration app with JSON to connect and post to MYSQL database. I created the following IF/ELSE statements to check for vacant input boxes, password match, and correct email characters before allowing it to be entered into the DATABASE. The code continues to execute the JSON posting even after the passwords don't match , invalid email characters are entered , and vacant text boxes are submitted. Why is it not returning and continuing to execute the JSON code? try { if (!inputEmail.getText().toString().matches("[a-zA-Z0-9._-]+@[a-z]+.[a-z]+") && email.length() > 0) { Toast.makeText(getApplicationContext(), "Enter Valid Email Address", Toast.LENGTH_LONG).show(); return; } else if(name.equals("") || email.equals("")|| password.equals("")||check.equals("")) { Toast.makeText(getApplicationContext(), "Field Vaccant", Toast.LENGTH_LONG).show(); return; } // check if both password matches else if(!password.equals(checkpass)) { Toast.makeText(getApplicationContext(), "Password does not match", Toast.LENGTH_LONG).show(); return; } if (json.getString(KEY_SUCCESS) != null) { registerErrorMsg.setText(""); String res = json.getString(KEY_SUCCESS); if(Integer.parseInt(res) == 1){ // user successfully registred // Store user details in SQLite Database DatabaseHandler db = new DatabaseHandler(getApplicationContext()); JSONObject json_user = json.getJSONObject("user"); // Clear all previous data in database userFunction.logoutUser(getApplicationContext()); db.addUser(json_user.getString(KEY_NAME), json_user.getString(KEY_EMAIL), json.getString(KEY_UID), json_user.getString(KEY_CREATED_AT)); // Launch Dashboard Screen Intent dashboard = new Intent(getApplicationContext(), DashboardActivity.class); // Close all views before launching Dashboard dashboard.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP); startActivity(dashboard); // Close Registration Screen finish(); }else{ // Error in registration registerErrorMsg.setText("User already Registered"); } } } catch (JSONException e) { } } });

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• Is this an acceptable use of "ASCII arithmetic"?

  - by jmgant

  I've got a string value of the form 10123X123456 where 10 is the year, 123 is the day number within the year, and the rest is unique system-generated stuff. Under certain circumstances, I need to add 400 to the day number, so that the number above, for example, would become 10523X123456. My first idea was to substring those three characters, convert them to an integer, add 400 to it, convert them back to a string and then call replace on the original string. That works. But then it occurred to me that the only character I actually need to change is the third one, and that the original value would always be 0-3, so there would never be any "carrying" problems. It further occurred to me that the ASCII code points for the numbers are consecutive, so adding the number 4 to the character "0", for example, would result in "4", and so forth. So that's what I ended up doing. My question is, is there any reason that won't always work? I generally avoid "ASCII arithmetic" on the grounds that it's not cross-platform or internationalization friendly. But it seems reasonable to assume that the code points for numbers will always be sequential, i.e., "4" will always be 1 more than "3". Anybody see any problem with this reasoning? Here's the code. string input = "10123X123456"; input[2] += 4; //Output should be 10523X123456

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• getSharedPreferences not working for me with concerns to ListPreferences and Integers

  - by ideagent

  I'm stuck at a point where I'm trying to get my project to read a preference value (from a ListPreference listing) and then use that value in a basic mathematical subtraction instance. The problem is that the "seek" preference is not being seen by my Java code, and yet the default value is (I've tried the default value with 3000 and now 0). Am i missing something, is there a bug here, known or unknown? Java code chunk where the issues manifests itself: public static final String PREF_FILE_NAME = "preferences"; seekback.setOnClickListener(new Button.OnClickListener() { @Override public void onClick(View view) { try { SharedPreferences preferences = getSharedPreferences(PREF_FILE_NAME, MODE_PRIVATE); Integer storedPreference = preferences.getInt("seek", 0); (mediaPlayer.getCurrentPosition()-storedPreference); } catch (Exception e) { e.printStackTrace(); } } }); Here are some other code bits for my project: From preferences file: <ListPreference android:entries="@array/seconds" android:entryValues="@array/seconds_values" android:summary="sets the seek interval for the seekback and seekforward buttons" android:title="Seek Interval" android:defaultValue="5000" android:key="@string/seek" From strings file: seek From an array file: Five seconds Fifteen seconds Thirty seconds Sixty seconds 5000 15000 30000 60000 let me know if you need to see more code to figure this one out Thanks in advance for any help that can be offered. I've worked over this issue now for a few hours and I'm burnt, a second pair of eyes on it would be very much appreciated. Arg, not sure how to get the code and plain text to format nicely here, even tried the options, like Code Sample, no luck AndroidCoder

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• Open + Save .exe file in notepad makes it corrupted

  - by Jacob Kofoed

  Hi, I just published this simple console application that is supposed to show a textbox with the value of a setting called "userID" with value 1001. This works like a charm. Now what I need is to change this value outside the editor, from notepad etc. When I open the application a lot in there is non-sence (& o! -å Þþþ,o" Ü+) etc. but with a quick (ctrl + F) I found the value 1001, and changed this to some other integer. I ran the application again, and it failed, didn't even give any userful error-message. At a point I tried just opening a newly published non-corrupted version of the application, didn't change anything, then saved from notepad, and it were also corrupted. It seems like notepad can't open some characters or something. Do I need to publish the application in some specific text-unicode language or something? Help much appreciated :) I know it sounds like a stupid application, but it is just a test of concept :) I use vb.net for this

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• How to visually reject user input in a table?

  - by FX

  In the programming of a table-based application module (i.e. the user mostly enters tabular data in an already laid-out table), how would you reject user input for a given cell? The scenario is: the user edits the cell, enters something (text, picture, ...) and you want them to notice when they finish editing (hitting enter, for example) that their entry is not valid for your given "format" (in the wider meaning: it can be that they entered a string instead of a number, that their entry is too long, too short, they include a picture while it's not acceptable, ...). I can see two different things happening: You can rather easily fit their entry into your format, and you do so, but you want them to notice it so they can change if your guess is not good enough (example: they entered "15.47" in a field that needs to be an integer, so your program makes it "15") You cannot guess what to do with their entry, and want to inform them that it's not valid. My question specifically is: what visual display can you offer to inform the user that his input is invalid? Is it preferable to refuse to leave the editing mode, or not? The two things I can imagine are: using colors (red background if invalid, yellow background for my case 1 above) when you reject an input, do something like Apple does for password entry of user accounts: you make the cell "shaking" (i.e. oscillating left and right) for one second, and keep the focus/editing in their so they don't loose what they've typed. Let's hear your suggestions. PS: This question is, at least in my thought process, somehow a continuation and a specialization of my previous question on getting users to read error messages. PPS: Made this community wiki, was that the right thing to do on this kind of question or not?

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• Strange behavior while returning csv file from spring controller

  - by Fanooos

  I working in a spring application which have an action method that returns a CSV file. This action works fine but in some cases it throws a predefined exception (MyAppException). I have another method that is annotated @ExceptionHandler(MyAppException.class) In the exception handler method I return another csv file but with different contents. The code that returns the csv file is almost the same in the two methods. List<String[]> list= new ArrayList<String[]>(); list.add(new String[]{ integrationRequestErrorLog.getErrorMessage(), Long.toString(integrationRequestErrorLog.getId()), Integer.toString(integrationRequestErrorLog.getErrorCode()) }); CSVWriter writer = new CSVWriter(response.getWriter(), ','); writer.writeAll(list); writer.close(); the difference between the two method is the list of contents. In the first method the file is returned normally while in the exception handler method I have a strange behavior. The exception handler method works fine with Opera browser while it gives me a 404 with FireFox. Opera browser give me 404 also but it download the file while firefox does not? Really I do not understand what is the difference here.

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• Finding the digit root of a number

  - by Jessica M.

  Study question is to find the digit root of a already provided number. The teacher provides us with the number 2638. In order to find the digit root you have to add each digit separately 2 + 6 + 3 + 8 = 19. Then you take the result 19 and add those two digits together 1 + 9 = 10. Do the same thing again 1 + 0 = 1. The digit root is 1. My first step was to use the variable total to add up the number 2638 to find the total of 19. Then I tried to use the second while loop to separate the two digits by using the % I have to try and solve the problem by using basic integer arithmetic (+, -, *, /). 1.Is it necessary and or possible to solve the problem using nested while loops? 2.Is my math correct? 3. As I wrote it here it does not run in Eclipse. Am I using the while loops correctly? import acm.program.*; public class Ch4Q7 extends ConsoleProgram { public void run(){ println("This program attempts to find the digit root of your number: "); int n = readInt("Please enter your number: "); int total = 0; int root = total; while (n > 0 ){ total = total + (n %10); n = (n / 10); } while ( total > 0 ){ root = total; total = ((total % 10) + total / 10); } println("your root should be " + root); } }

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• sqlalchemy dynamic mapping

  - by adancu

  Hi, I have the following problem: I have the class: class Word(object): def __init__(self): self.id = None self.columns = {} def __str__(self): return "(%s, %s)" % (str(self.id), str(self.columns)) self.columns is a dict which will hold (columnName:columnValue) values. The name of the columns are known at runtime and they are loaded in a wordColumns list, for example wordColumns = ['english', 'korean', 'romanian'] wordTable = Table('word', metadata, Column('id', Integer, primary_key = True) ) for columnName in wordColumns: wordTable.append_column(Column(columnName, String(255), nullable = False)) I even created a explicit mapper properties to "force" the table columns to be mapped on word.columns[columnName], instead of word.columnName, I don't get any error on mapping, but it seems that doesn't work. mapperProperties = {} for column in wordColumns: mapperProperties['columns[\'%']' % column] = wordTable.columns[column] mapper(Word, wordTable, mapperProperties) When I load a word object, SQLAlchemy creates an object which has the word.columns['english'], word.columns['korean'] etc. properties instead of loading them into word.columns dict. So for each column, it creates a new property. Moreover word.columns dictionary doesn't even exists. The same way, when I try to persist a word, SQLAlchemy expects to find the column values in properties named like word.columns['english'] (string type) instead of the dictionary word.columns. I have to say that my experience with Python and SQLAlchemy is quite limited, maybe it isn't possible to do what I'm trying to do. Any help appreciated, Thanks in advance.

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• Array: Recursive problem cracked me up

  - by VaioIsBorn

  An array of integers A[i] (i 1) is defined in the following way: an element A[k] ( k 1) is the smallest number greater than A[k-1] such that the sum of its digits is equal to the sum of the digits of the number 4* A[k-1] . You need to write a program that calculates the N th number in this array based on the given first element A[1] . INPUT: In one line of standard input there are two numbers seperated with a single space: A[1] (1 <= A[1] <= 100) and N (1 <= N <= 10000). OUTPUT: The standard output should only contain a single integer A[N] , the Nth number of the defined sequence. Input: 7 4 Output: 79 Explanation: Elements of the array are as follows: 7, 19, 49, 79... and the 4th element is solution. I tried solving this by coding a separate function that for a given number A[k] calculates the sum of it's digits and finds the smallest number greater than A[k-1] as it says in the problem, but with no success. The first testing failed because of a memory limit, the second testing failed because of a time limit, and now i don't have any possible idea how to solve this. One friend suggested recursion, but i don't know how to set that. Anyone who can help me in any way please write, also suggest some ideas about using recursion/DP for solving this problem. Thanks.

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• notify url is not called

  - by Jahangeer Ahmed

  Dim redirecturl As String = "" redirecturl = ConfigurationManager.AppSettings("papalUrl").ToString() & "us/cgi-bin/webscr?cmd=_cart&upload=1&business=" & ConfigurationManager.AppSettings("paypalemail").ToString() Dim j As Integer = 0 Dim dr1 As DataRow If ds.Tables("ReviewOrder").Rows.Count 0 Then Dim requestsFile As String = Server.MapPath("~/App_Data/PaymentRequests.xml") ' ds.Tables("ReviewOrder").WriteXml(requestsFile) For j = 0 To ds.Tables("ReviewOrder").Rows.Count - 1 dr1 = ds.Tables("ReviewOrder").Rows(j) redirecturl += "&item_name_" & j + 1 & "=" & dr1("varTitle") redirecturl += "&amount_" & j + 1 & "=" & dr1("flRate") redirecturl += "&image_url_" & j + 1 & "=" & ConfigurationManager.AppSettings("RSSurl").ToString() & dr1("imgImage") redirecturl += "&quantity_" & j + 1 & "=" & Convert.ToInt64(dr1("flQuantity")) ''redirecturl += "&item_name_2=Sample_testing2&amount_2=9.50" ''redirecturl += "&quantity_2=2" ''redirecturl += "&item_name_3=Sample_testing3" ''redirecturl += "&amount_3=8.50" ''redirecturl += "&quantity_3=3" redirecturl += "&custom_" & j + 1 & "=" & dr1("BasketID") Next End If redirecturl += "&currency=" & ConfigurationManager.AppSettings("CurrencyCode").ToString() redirecturl += "&first_name=" & firstName redirecturl += "&last_name=" & lastName redirecturl += "&city=" & city redirecturl += "&state=" & state redirecturl += "&zip=" & zip redirecturl += "&address1=" & address1 redirecturl += "&address2=" & address2 redirecturl += "&notify_url=" & Server.UrlEncode(ConfigurationManager.AppSettings("NotifyUrl").ToString() & "&rm=2") redirecturl += "&return=" & ConfigurationManager.AppSettings("SuccessURL").ToString() 'Failed return page url redirecturl += "&cancel_return=" & ConfigurationManager.AppSettings("FailedURL").ToString() Page.ClientScript.RegisterClientScriptBlock(Me.GetType(), "Redirect", "window.parent.location='" & redirecturl & "';", True)

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• Concise description of how .h and .m files interact in objective c?

  - by RJ86

  I have just started learning objective C and am really confused how the .h and .m files interact with each other. This simple program has 3 files: Fraction.h #import <Foundation/NSObject.h> @interface Fraction : NSObject { int numerator; int denominator; } - (void) print; - (void) setNumerator: (int) n; - (void) setDenominator: (int) d; - (int) numerator; - (int) denominator; @end Fraction.m #import "Fraction.h" #import <stdio.h> @implementation Fraction -(void) print { printf( "%i/%i", numerator, denominator ); } -(void) setNumerator: (int) n { numerator = n; } -(void) setDenominator: (int) d { denominator = d; } -(int) denominator { return denominator; } -(int) numerator { return numerator; } @end Main.m #import <stdio.h> #import "Fraction.h" int main(int argc, char *argv[]) { Fraction *frac = [[Fraction alloc] init]; [frac setNumerator: 1]; [frac setDenominator: 3]; printf( "The fraction is: " ); [frac print]; printf( "\n" ); [frac release]; return 0; } From what I understand, the program initially starts running the main.m file. I understand the basic C concepts but this whole "class" and "instance" stuff is really confusing. In the Fraction.h file the @interface is defining numerator and denominator as an integer, but what else is it doing below with the (void)? and what is the purpose of re-defining below? I am also quite confused as to what is happening with the (void) and (int) portions of the Fraction.m and how all of this is brought together in the main.m file. I guess what I am trying to say is that this seems like a fairly easy program to learn how the different portions work with each other - could anyone explain in non-tech jargon?

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• Help with active record relations

  - by Christian Fazzini

  class CreateActivities < ActiveRecord::Migration def self.up create_table :activities do |t| t.references :user t.references :media t.integer :artist_id t.string :type t.timestamps end end def self.down drop_table :activities end end class Fan < Activity belongs_to :user, :counter_cache => true end class Activity < ActiveRecord::Base belongs_to :user belongs_to :media belongs_to :artist, :class_name => 'User', :foreign_key => 'artist_id' end class User < ActiveRecord::Base has_many :activities has_many :fans end I tried changing my activity model too, without any success: class Activity < ActiveRecord::Base has_many :activities, :class_name => 'User', :foreign_key => 'user_id' has_many :activities, :class_name => 'User', :foreign_key => 'artist_id' end One thing to note. Activity is an STI. Fan inherits from Activity. In console, I do: # Create a fan object. User is a fan of himself fan = Fan.new => #<Fan id: nil, user_id: nil, media_id: nil, artist_id: nil, type: "Fan", comment: nil, created_at: nil, updated_at: nil> # Assign a user object fan.user = User.first => #<User id: 1, genre_id: 1, country_id: 1, .... # Assign an artist object fan.artist_id = User.first.id => 1 # Save the fan object fan.save! => true Activity.last => #<Fan id: 13, user_id: 1, media_id: nil, artist_id: 1, type: "Fan", comment: nil, created_at: "2010-12-30 08:41:25", updated_at: "2010-12-30 08:41:25"> Activity.last.user => #<User id: 1, genre_id: 1, country_id: 1, ..... But... Activity.last.artist => nil Why is Activity.last.artist returning nil?

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• How do i access EJB implementing remote interface in separate web application?

  - by Nitesh Panchal

  Hello, I am using Netbeans 6.8 and Glassfish v3.0. I created an ejb module and created entity classes from database and then created stateless session bean with remote interface. Say eg. @Remote public interface customerRemote{ public void add(String name, String address); public Customer find(Integer id); } @Stateless public class customerBean implements customerRemote{ //implementations of methods } Then i created a new web application. But now how do i access remote ejb's in my web application. I could lookup a bean with jndi name but what i want to know is, what type of object it will return? How do i typecast it in customerRemote? I don't have any class named customerRemote in my web application. So, how do i do it? Also, what about the entity class Customer? There is no such class named Customer in my web application also. All ejb's and entity classes are in separate ejb module. Please help me :(

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• Are there equivalents to Ruby's method_missing in other languages?

  - by Justin Ethier

  In Ruby, objects have a handy method called method_missing which allows one to handle method calls for methods that have not even been (explicitly) defined: Invoked by Ruby when obj is sent a message it cannot handle. symbol is the symbol for the method called, and args are any arguments that were passed to it. By default, the interpreter raises an error when this method is called. However, it is possible to override the method to provide more dynamic behavior. The example below creates a class Roman, which responds to methods with names consisting of roman numerals, returning the corresponding integer values. class Roman def romanToInt(str) # ... end def method_missing(methId) str = methId.id2name romanToInt(str) end end r = Roman.new r.iv #=> 4 r.xxiii #=> 23 r.mm #=> 2000 For example, Ruby on Rails uses this to allow calls to methods such as find_by_my_column_name. My question is, what other languages support an equivalent to method_missing, and how do you implement the equivalent in your code?

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• what's the performance difference between int and varchar for primary keys

  - by user568576

  I need to create a primary key scheme for a system that will need peer to peer replication. So I'm planning to combine a unique system ID and a sequential number in some way to come up with unique ID's. I want to make sure I'll never run out of ID's, so I'm thinking about using a varchar field, since I could always add another character if I start running out. But I've read that integers are better optimized for this. So I have some questions... 1) Are integers really better optimized? And if they are, how much of a performance difference is there between varchars and integers? I'm going to use firebird for now. But I may switch later. Or possibly support multiple db's. So I'm looking for generalizations, if that's possible. 2) If integers are significantly better optimized, why is that? And is it likely that varchars will catch up in the future, so eventually it won't matter anyway? My varchar keys won't have any meaning, except for the unique system ID part. But I may want to obscure that somehow. Also, I plan to efficiently use all the bits of each character. I don't, for example, plan to code the integer 123 as the character string "123". So I don't think varchars will require more space than integers.

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• How to keep track of call statistics? C++

  - by tf.rz

  I'm working on a project that delivers statistics to the user. I created a class called Dog, And it has several functions. Speak, woof, run, fetch, etc. I want to have a function that spits out how many times each function has been called. I'm also interested in the constructor calls and destructor calls as well. I have a header file which defines all the functions, then a separate .cc file that implements them. My question is, is there a way to keep track of how many times each function is called? I have a function called print that will fetch the "statistics" and then output them to standard output. I was considering using static integers as part of the class itself, declaring several integers to keep track of those things. I know the compiler will create a copy of the integer and initialize it to a minimum value, and then I'll increment the integers in the .cc functions. I also thought about having static integers as a global variable in the .cc. Which way is easier? Or is there a better way to do this? Any help is greatly appreciated!

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• Will this class cause memory leaks, and does anything need disposing of? (asp.net vb)

  - by Phil

  Here is the class to export a gridview to an excel sheet: Imports System Imports System.Data Imports System.Configuration Imports System.IO Imports System.Web Imports System.Web.Security Imports System.Web.UI Imports System.Web.UI.WebControls Imports System.Web.UI.WebControls.WebParts Imports System.Web.UI.HtmlControls Namespace ExcelExport Public NotInheritable Class GVExportUtil Private Sub New() End Sub Public Shared Sub Export(ByVal fileName As String, ByVal gv As GridView) HttpContext.Current.Response.Clear() HttpContext.Current.Response.AddHeader("content-disposition", String.Format("attachment; filename={0}", fileName)) HttpContext.Current.Response.ContentType = "application/ms-excel" Dim sw As StringWriter = New StringWriter Dim htw As HtmlTextWriter = New HtmlTextWriter(sw) Dim table As Table = New Table table.GridLines = GridLines.Vertical If (Not (gv.HeaderRow) Is Nothing) Then GVExportUtil.PrepareControlForExport(gv.HeaderRow) table.Rows.Add(gv.HeaderRow) End If For Each row As GridViewRow In gv.Rows GVExportUtil.PrepareControlForExport(row) table.Rows.Add(row) Next If (Not (gv.FooterRow) Is Nothing) Then GVExportUtil.PrepareControlForExport(gv.FooterRow) table.Rows.Add(gv.FooterRow) End If table.RenderControl(htw) HttpContext.Current.Response.Write(sw.ToString) HttpContext.Current.Response.End() End Sub Private Shared Sub PrepareControlForExport(ByVal control As Control) Dim i As Integer = 0 Do While (i < control.Controls.Count) Dim current As Control = control.Controls(i) If (TypeOf current Is LinkButton) Then control.Controls.Remove(current) control.Controls.AddAt(i, New LiteralControl(CType(current, LinkButton).Text)) ElseIf (TypeOf current Is ImageButton) Then control.Controls.Remove(current) control.Controls.AddAt(i, New LiteralControl(CType(current, ImageButton).AlternateText)) ElseIf (TypeOf current Is HyperLink) Then control.Controls.Remove(current) control.Controls.AddAt(i, New LiteralControl(CType(current, HyperLink).Text)) ElseIf (TypeOf current Is DropDownList) Then control.Controls.Remove(current) control.Controls.AddAt(i, New LiteralControl(CType(current, DropDownList).SelectedItem.Text)) ElseIf (TypeOf current Is CheckBox) Then control.Controls.Remove(current) control.Controls.AddAt(i, New LiteralControl(CType(current, CheckBox).Checked)) End If If current.HasControls Then GVExportUtil.PrepareControlForExport(current) End If i = (i + 1) Loop End Sub End Class End Namespace Will this class cause memory leaks? And does anything here need to be disposed of? The code is working but I am getting the app pool falling over frequently when it is in use. Thanks.

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• How to define default values optional fields in play framework forms?

  - by natalinobusa

  I am implementing a web api using the scala 2.0.2 play framework. I would like to extract and validate a number of get parameters. And for this I am using a play "form" which allows me to define optional fields. Problem: For those optional fields, I need to define a default value if the parameter is not passed. The code is intended to parse correctly these three use cases: /test?top=abc (error, abc is not an integer) /test?top=123 (valid, top is 123) /test (valid, top is 42 (default value)) I have come up with the following code: def test = Action { implicit request => case class CData(top:Int) val p = Form( mapping( "top" -> optional(number) )((top) => CData($top.getOrElse(42))) ((cdata:CData) => Some(Some(cdata.top))) ).bindFromRequest() Ok("all done.") } The code works, but it's definitely not elegant. There is a lot of boiler plate going on just to set up a default value for a missing request parameter. Can anyone suggest a cleaner and more coincise solution?

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