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• When to trash hashmap contents to avoid performance degradation?

  - by Jack

  Hello, I'm woking on Java with a large (millions) hashmap that is actually built with a capacity of 10.000.000 and a load factor of .75 and it's used to cache some values since cached values become useless with time (not accessed anymore) but I can't remove useless ones while on the way I would like to entirely empty the cache when its performance starts to degrade. How can I decide when it's good to do it? For example, with 10 millions capacity and .75 should I empty it when it reaches 7.5 millions of elements? Because I tried various threshold values but I would like to have an analytic one. I've already tested the fact that emping it when it's quite full is a boost for perfomance (first 2-3 algorithm iterations after the wipe just fill it back, then it starts running faster than before the wipe) Thanks

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• Constructor with non-instance variable assistant?

  - by Robert Fischer

  I have a number of classes that look like this: class Foo(val:BasicData) extends Bar(val) { val helper = new Helper(val) val derived1 = helper.getDerived1Value() val derived2 = helper.getDerived2Value() } ...except that I don't want to hold onto an instance of "helper" beyond the end of the constructor. In Java, I'd do something like this: public class Foo { final Derived derived1, derived2; public Foo(BasicData val) { Helper helper = new Helper(val); derived1 = helper.getDerived1Value(); derived2 = helper.getDerived2Value(); } } So how do I do something like that in Scala? I'm aware of creating a helper object of the same name of the class with an apply method: I was hoping for something slightly more succinct.

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• mysql conditional query - complicated!

  - by emre

  i want to get distinct values for a field, let say: field1... ok this needs a query like: "select distint(field1) from table" however for some records, field1 is empty and there is another column that is an alternative to field1, which is field2. now; for the records where field1 is empty i need to use the value of field2. i think i need sort of a conditional select statement with if control something like: "select distinct( (if(field1!='') field1 else field2) ) from table" but i have no idea on how to write it. any help is appricated...

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• java.text.DecimalFormat blank when zero?

  - by Eduardo

  Is it possible to show blank (empty string) when the number is zero (0)? (strict no zeros at left)

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• Can I use memcpy in C++ to copy classes that have no pointers or virtual functions

  - by Shane MacLaughlin

  Say I have a class, something like the following; class MyClass { public: MyClass(); int a,b,c; double x,y,z; }; #define PageSize 1000000 MyClass Array1[PageSize],Array2[PageSize]; If my class has not pointers or virtual methods, is it safe to use the following? memcpy(Array1,Array2,PageSize*sizeof(MyClass)); The reason I ask, is that I'm dealing with very large collections of paged data, as decribed here, where performance is critical, and memcpy offers significant performance advantages over iterative assignment. I suspect it should be ok, as the 'this' pointer is an implicit parameter rather than anything stored, but are there any other hidden nasties I should be aware of?

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• Code won't exit foreach block

  - by Matt

  I've got the following C# code segment that takes a list, finds objects that are ready to update, then shoves them into a temp list, deletes from the main list, and then goes on its merry way. My issue is that the foreach block, which cycles through my main list, won't exit. TempLog.Clear(); //Ensure TempLog is empty foreach (CLogger ready in PlayerLog) { if (ready.UpdateReady == true) // Record is ready to be updated in database { TempLog.Add(ready); // Add record to templog PlayerLog.Remove(ready); // Remove from playerlog } } <---- Never reaches this point if (TempLog.Count > 0) // Just check that templog isn't empty { new Thread(Update).Start(); // Run update code } I've put heaps of debugging in, and I can watch PlayerLog start at 1, TempLog at 0, then it enters the foreach loop, picks up that the record UpdateReady flag is on, TempLog goes to 1, PlayerLog goes to 0, then it just stops.. No errors, just stops.. Thanks for the help :)

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• Emulator batteryService not working

  - by user568551

  So i've got a 1.6 emulator running. I have a receiver with action power connected and disconnected filters. when i connect to the emulator through telnet and issue the power ac on or power ac off command, logcat shows: 01-11 21:33:01.096: ERROR/BatteryService(67): Could not open '/sys/class/power_supply/usb/online' 01-11 21:33:01.104: ERROR/BatteryService(67): Could not open '/sys/class/power_supply/battery/batt_vol' 01-11 21:33:01.104: ERROR/BatteryService(67): Could not open '/sys/class/power_supply/battery/batt_temp' and my receiver does not get activated. It was working just fine yesterday and now it does not. I tried reinstalling the AVD, and also deleted and reinstalled the SDK from the SDK manager. Works fine in my 2.2 emulator. Any ideas?

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• Unmanaged C++ instantiation question

  - by Jim Jones

  Want to verify that my understanding of how this works. Have an unmanaged C++ Class with one public instance variable: char* character_encoding; and whose only constructor is defined as: TF_StringList(const char* encoding = "cp_1252"); when I use this class in either managed or unmanaged C++, the first thing I do is declare a pointer to an object of this class: const TF_StringList * categories; Then later I instantiate it: categories = new TF_StringList(); this gives me a pointer to an object of type TF_StringList whose variable character_encoding is set to "cp_1252"; So, is all that logic valid? Jim

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• Reading file data during form's clean method

  - by Dominic Rodger

  So, I'm working on implementing the answer to my previous question. Here's my model: class Talk(models.Model): title = models.CharField(max_length=200) mp3 = models.FileField(upload_to = u'talks/', max_length=200) Here's my form: class TalkForm(forms.ModelForm): def clean(self): super(TalkForm, self).clean() cleaned_data = self.cleaned_data if u'mp3' in self.files: from mutagen.mp3 import MP3 if hasattr(self.files['mp3'], 'temporary_file_path'): audio = MP3(self.files['mp3'].temporary_file_path()) else: # What goes here? audio = None # setting to None for now ... return cleaned_data class Meta: model = Talk Mutagen needs file-like objects - the first case (where the uploaded file is larger than the size of file handled in memory) works fine, but I don't know how to handle InMemoryUploadedFile that I get otherwise. I've tried: # TypeError (coercing to Unicode: need string or buffer, InMemoryUploadedFile found) audio = MP3(self.files['mp3']) # TypeError (coercing to Unicode: need string or buffer, cStringIO.StringO found) audio = MP3(self.files['mp3'].file) # Hangs seemingly indefinitely audio = MP3(self.files['mp3'].file.read()) Is there something wrong with mutagen, or am I doing it wrong?

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• Compile a binary file for linking OSX

  - by Satpal

  I'm trying to compile a binary file into a MACH_O object file so that it can be linked it into a dylib. The dylib is written in c/c++. On linux the following command is used: ld -r -b binary -o foo.o foo.bin I have tried various option on OSX but to no avail: ld -r foo.bin -o foo.o gives: ld: warning: -arch not specified ld: warning: ignoring file foo.bin, file was built for unsupported file format which is not the architecture being linked (x86_64) An empty .o file is created ld -arch x86_64 -r foo.bin -o foo.o ld: warning: ignoring file foo.bin, file was built for unsupported file format which is not the architecture being linked (x86_64) Again and empty .o file is created. Checking the files with nm gives: nm foo.o nm: no name list The binary file is actually, firmware that will be downloaded to an external device. Thanks for looking

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• Map null column as 0 in a legacy database (JPA)

  - by Indrek

  Using Play! framework and it's JPASupport class I have run into a problem with a legacy database. I have the following class: @Entity @Table(name="product_catalog") public class ProductCatalog extends JPASupport { @Id @GeneratedValue(strategy = GenerationType.IDENTITY) public Integer product_catalog; @OneToOne @JoinColumn(name="upper_catalog") public ProductCatalog upper_catalog; public String name; } Some product catalogs don't have an upper catalog, and this is referenced as 0 in a legacy database. If I supply the upper_catalog as NULL, then expectedly JPA inserts a NULL value to that database column. How could I force the null values to be 0 when writing to the database and the other way around when reading from the database?

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• 0.20.2 API hadoop version with java 5

  - by abdeslam

  I have started a maven project trying to implement the MapReduce algorithm in java 1.5.0_14. I have chosen the 0.20.2 API hadoop version. In the pom.xml i'm using thus the following dependency: < dependency < groupId>org.apache.hadoop< /groupId> < artifactId>hadoop-core< /artifactId> < version>0.20.2< /version> < /dependency But when I'm using an import to the org.apache.hadoop classes, I get the following error: bad class file: ${HOME_DIR}\repository\org\apache\hadoop\hadoop-core\0.20.2\hadoop-core-0.20.2.jar(org/apache/hadoop/fs/Path.class) class file has wrong version 50.0, should be 49.0. Does someone know how can I solve this issue. Thanks.

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• django form creation on init

  - by John

  Hi, How can I add a field in the form init function? e.g. in the code below I want to add a profile field. class StaffForm(forms.ModelForm): def __init__(self, user, *args, **kwargs): if user.pk == 1: self.fields['profile'] = forms.CharField(max_length=200) super(StaffForm, self).__init__(*args, **kwargs) class Meta: model = Staff I know I can add it just below the class StaffForm.... line but I want this to be dynamic depending on what user is passed in so can't do it this way. Thanks

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• C++ design with static methods

  - by user231536

  I would like to define as class X with a static method: class X { static string get_type () {return "X";} //other virtual methods } I would like to force classes which inherit from X to redefine the get_type() method and return strings different from "X" (I am happy if they just redefine get_type for now). How do I do this? I know that I cannot have virtual static methods. Edit: The question is not about the type_id, but in general about a static method that should be overriden. For example class X { static int getid() {return 1;} }

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• How to Add Horizontal line in Javascript

  - by user54197

  I would like to add a horizontal seperating line on a dynamic populated table. How do I do this? Below is a snippet. function addNewRow() { $('#displayTable tr:last').after('<tr><td style="font-size:smaller;" class="dataField1"></td><td style="font-size:smaller;" class="dataField2"></td><td style="font-size:smaller;" class="dataField3"></td></tr>'); var $tr = $('#displayTable tr:last'); $tr.find('.dataField1').text($('#txtName').val()); $tr.find('.dataField2').text($('#txtAddress').val()); $tr.find('.dataField3').text('document.write("<tr><td colspan=\"2\"><hr \/><\/td><\/tr>"); }

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• Can I write functors using a private nested struct?

  - by Kristo

  Given this class: class C { private: struct Foo { int key1, key2, value; }; std::vector<Foo> fooList; }; The idea here is that fooList can be indexed by either key1 or key2 of the Foo struct. I'm trying to write functors to pass to std::find so I can look up items in fooList by each key. But I can't get them to compile because Foo is private within the class (it's not part of C's interface). Is there a way to do this without exposing Foo to the rest of the world? (note: I've got to run to a meeting. I'll be able to post more sample code in about a half hour.)

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• How do I dynamically add and remove line items from an ASP.NET MVC view?

  - by Mike Roosa

  I have a PurchaseOrder model: public class PurchaseOrder { public string OrderNumber { get; set; } public string Customer { get; set; } public IList<LineItem> Lines { get; set; } } and a LineItem class: public class LineItem { public string PartNumber { get; set; } public int Quantity { get; set; } } What I want to do is on my view for the PurhcaseOrder Create action, I need a section for line items. The user should be able to add a new line, remove a line, then submit. One caveat is the PartNumber needs to be a dropdown list of valid parts. What can I do to accomplish what I'm looking for?

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• Best way to test instance methods without running __init__

  - by KenFar

  I've got a simple class that gets most of its arguments via init, which also runs a variety of private methods that do most of the work. Output is available either through access to object variables or public methods. Here's the problem - I'd like my unittest framework to directly call the private methods called by init with different data - without going through init. What's the best way to do this? So far, I've been refactoring these classes so that init does less and data is passed in separately. This makes testing easy, but I think the usability of the class suffers a little. EDIT: Example solution based on Ignacio's answer: import types class C(object): def __init__(self, number): new_number = self._foo(number) self._bar(new_number) def _foo(self, number): return number * 2 def _bar(self, number): print number * 10 #--- normal execution - should print 160: ------- MyC = C(8) #--- testing execution - should print 80 -------- MyC = object.__new__(C) MyC._bar(8)

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• Polymorphic classes in templates

  - by soxarered

  Let's say we have a class hierarchy where we have a generic Animal class, which has several classes directly inherit from it (such as Dog, Cat, Horse, etc..). When using templates on this inheritance hierarchy, is it legal to just use SomeTemplateClass<Animal> and then shove in Dogs and Cats and Horses into this templated object? For example, assume we have a templated Stack class, where we want to host all sorts of animals. Can I simply state Stack<Animal> s; Dog d; s.push(d); Cat c; s.push(c);

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• What Can A 'TreeDict' (Or Treemap) Be Used For In Practice?

  - by Seun Osewa

  I'm developing a 'TreeDict' class in Python. This is a basically a dict that allows you to retrieve its key-value pairs in sorted order, just like the Treemap collection class in Java. I've implemented some functionality based on the way unique indexes in relational databases can be used, e.g. functions to let you retrieve values corresponding to a range of keys, keys greater than, less than or equal to a particular value in sorted order, strings or tuples that have a specific prefix in sorted order, etc. Unfortunately, I can't think of any real life problem that will require a class like this. I suspect that the reason we don't have sorted dicts in Python is that in practice they aren't required often enough to be worth it, but I want to be proved wrong. Can you think of any specific applications of a 'TreeDict'? Any real life problem that would be best solved by this data structure? I just want to know for sure whether this is worth it.

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• Confused about "override" vs. "new" in C#

  - by iTayb

  I'm having the following classes: class Base { public virtual void Print() { Console.WriteLine("Base"); } } class Der1 : Base { public new virtual void Print() { Console.WriteLine("Der1"); } } class Der2 : Der1 { public override void Print() { Console.WriteLine("Der2"); } } This is my main method: Base b = new Der2(); Der1 d1 = new Der2(); Der2 d2 = new Der2(); b.Print(); d1.Print(); d2.Print(); The output is Base, Der2, Der2. As far as I know, Override won't let previous method to run, even if the pointer is pointing to them. So the first line should output Der2 as well. However Base came out. How is it possible? How the override didn't work there?

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• having trouble with a mysql query

  - by chuck akers

  this keeps saying Warning: mysql_num_rows() expects parameter 1 to be resource, boolean given in directory here the error is near the login_query variable, can someone help me fix it. <?php if (isset($_POST['login_username'], $_POST['login_password'])) { $login_username = trim(mysql_real_escape_string(htmlentities($_POST['login_username']))); $login_password = md5(trim(mysql_real_escape_string(htmlentities($_POST['login_password'])))); if (!empty($login_username) && !empty($login_password)) { $login_query = mysql_query("SELECT user_id FROM username WHERE username='".$login_username."' AND password='".$login_password."'"); if (mysql_num_rows($login_query)==1) { $user_id = mysql_result($login_query, 0, 'user_id'); $_SESSION['user_id'] = $user_id; header('Location: index.php'); die(); } }} ?

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• Allowing AsyncTask to Manipulate Values in Different Activity Classes

  - by Matt

  Hi guys, This title may seem strange, so let me try to explain what I'm trying to do. I have several activity classes, each representing a different view in my application. My initial activity class gets loaded when the application launches. The user enters values and eventually a TCP socket is opened, and I then use AsyncTask to listen for and respond to messages from the server. I'd like for this AsyncTask class to essentially listen until the app is closed/error condition reached, and be able to update values in other activity classes after they are started. Does this make sense (it's been a long, frustrating night)? I know that static activity class references are bad practice, and touching the UI thread from other activities is bad as well, but I'm having trouble finding a clean solution to this problem. Maybe using AsyncTask is not the best approach here? Should I be using a service instead or something else entirely? Thanks in advance.

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• Reuse C++ Header files

  - by Amrish

  Guys, I have a Visual C++ solution with 2 projects AlgorithmA & AlgorithmB and both share a common header file RunAlgo.h with the class declaration. Each project in the solution has its own unique implementation for the header file. I am trying to compile a DLL out of the common header file RunAlgo.h and add reference to this DLL in the projects AlgorithmA & AlgorithmB. I have then included separate RunAlgo.cpp definition file in both my projects. The problem is that I am getting linker errors while compiling the new DLL project which has only the header file. So, the question is Can a header file with only class declaration be compiled into a DLL (Similar to class library containing an Interface in C#)? For the above scenario, is there a better approach to reuse the common Header file among projects? Should the above method work (re-check my code?)

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• determine from where the function being called in php

  - by Avinash

  I have one function on my code. say its xyz(). This function is being called from different files of my project. Is there any way than I can get from where the function is being called. I want below infromation: File name from where its called. Line number of that file. if call is from inside the function then that function name. Class name Class method name. I know about use of magic constants like FILE and all that. but i don't want to pass all that in function call. like below: xyz('msg',__FILE__,__CLASS__); is there any way that i have to pass just my error related data only. and it will find the above details from where the function is called. let me know if anything is not clear.

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