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• What is the right way to implement communication between java objects?

  - by imoschak

  I'm working on an academic project which simulates a rather large queuing procedure in java. The core of the simulator rests within one package where there exist 8 classes, each one implementing a single concept. Every class in the project follows SRP. These classes encapsulate the behavior of the simulator and inter-connect every other class in the project. The problem that has arisen is that most of these 8 classes are, as is logical i think, tightly coupled and each one has to have working knowledge of every other class in this package in order to be able to call methods from it when needed. The application needs only one instance of each class so it might be better to create static fields for each class in a new class and use that to make calls -instead of preserving a reference in each class for every other class in the package (which I'm certain that is incorrect)-, but is this considered a correct design solution? or is there a design pattern maybe that better suits my needs?

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• What is the most efficient way to pass data (list of pairs of [Integer + Double]) between two Google App Engine instances?

  - by ruslan

  What is the most efficient way to pass data (list of pairs of [Integer, Double]) between two Google App Engine instances ? Currently I use Java binary serialization. Frontend servlet receives data from the client in JSON format. I convert it to byte[] using ObjectOutput.writeObject and then send it to backend servlet via HTTP POST. It's not in production yet. Should I just pass client's JSON as it is to backend? It seems more logical. But it's bigger in size. Or should I use Google Protocol Buffers as stated in this benchmark article ? Thank you!!!

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• Testing what a String token holds

  - by Yiwei Gao

  I am making a calculator and part of this program takes in user String input and tokenizes it (using my own implementation of a Tokenizer class). So now I have a bunch of Token objects and I would like to test each one of them to see if they hold numbers or operators. Is there a way to test to see if they hold operators (ie. +, -, *, /, =, (, ), etc.) without using if (token.equals("+") || token.equals("-") || ... and so on, for each operator? These Token objects are all of type String.

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• fastest method for minimum of two numbers

  - by user85030

  I was going through mit's opencourseware related to performance engineering. The quickest method (requiring least number of clock cycles) for finding the minimum of two numbers(say x and y) is stated as: min= y^((x^y) & -(x<y)) The output of the expression x < y can be 0 or 1 (assuming C is being used) which then changes to -0 or -1. I understand that xor can be used to swap two numbers. Questions: 1. How is -0 different from 0 and -1 in terms of binary? 2. How is that result used with the and operator to get the minimum? Thanks in advance.

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• select tag sits one pixel lower in Firefox than it does in Chrome

  - by sepoto

  #allday { width: 180px; height: 20px; margin-top: 2px !important; margin-right: 0px; padding: 0px; -webkit-appearance: menulist; box-sizing: border-box; -webkit-box-align: center; border: 1px solid; border-image: initial; white-space: pre; -webkit-rtl-ordering: logical; color: black; background-color: white; cursor: default; } I inspected the element in both browsers but I'm not really seeing where the discrepancy is. Has anyone been through this before with the select tag?

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• Casting an object which could be null

  - by DeeMac

  DateTime? testDate = (DateTime?)arrayOfObjects[dateObject]; Does that code look ok? I attempted to use the as operator but I got the 'non-nullable' error. What I'm trying to say is that the object I'm choosing from the array is either DateTime or a null DateTime but either can be assigned to testDate. Doesn't feel right doing it this way, I think I'm missing something obvious. EDIT: I suppose it's the same as the way I could've adapted the as in the following way: DateTime? testDate = arrayOfObjects[dateObject] as DateTime?; Is either line of code the best way of handling potential nulls?

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• Finding the specific type held in an ArrayList<Object> (ie. Object = String, etc.)

  - by Christopher Griffith

  Say I have an ArrayList that I have cast to an ArrayList of objects. I know that all the objects that were in the ArrayList I cast were of the same type, but not what the type was. Now, if the ArrayList is not empty, I could take one of the objects in it and use the instanceof operator to learn what the actual type is. But what of the case where the ArrayList is empty? How do I determine what type Object actually is then? Is it possible?

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• The Cash or Credit problem

  - by Josh K

  If you go to a store and ask "Cash or Credit?" they might simply say "Yes." This doesn't tell you anything as you posed an OR statement. if(cash || credit) With humans it's possible that they might respond "Both" to that question, or "Only {cash | credit}." Is there a way (or operator) to force the a statement to return the TRUE portions of a statement? For example: boolean cash = true; boolean credit = true; boolean cheque = false; if(cash || credit || cheque ) { // In here you would have an array with cash and credit in it because both of those are true }

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• How to stable_sort without copying?

  - by Mehrdad

  Why does stable_sort need a copy constructor? (swap should suffice, right?) Or rather, how do I stable_sort a range without copying any elements? #include <algorithm> class Person { Person(Person const &); // Disable copying public: Person() : age(0) { } int age; void swap(Person &other) { using std::swap; swap(this->age, other.age); } friend void swap(Person &a, Person &b) { a.swap(b); } bool operator <(Person const &other) const { return this->age < other.age; } }; int main() { static size_t const n = 10; Person people[n]; std::stable_sort(people, people + n); }

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• What types of conditions can be used for conditional compilation in C++?

  - by user1002288

  This is an exam question for C++: Which of the following statements accurately describe the condition that can be used for conditional compilation in C++? A. The condition can depend on the value of environment variables. B. The condition can depend on the value of any const variables. C. The condition can depend on the value of program variables. D. The condition can use the sizeof() operator to make decision about compiler-dependent operations based on the size of standard data type. E. The condition must evaluate to either a 0 or 1 during preprocessing. I think the answer is E. Is this correct?

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• How to know if the argument that is passed to the function is a class, union or enum in c++?

  - by Narek

  I want to define an operator<< for all enums, to cout the value and print that it is an enum like this: code: enum AnyEnum{A,B,C}; AnyEnum enm = A; cout << enm <<endl; output: This is an enum which has a value equal to 0 I know a way of doing this with Boost library by using is_enum struct. But I don’t understand how it works. So that's why, in general, I am interested how to identify if the veriable is a class type, union type or an enum (in compile time).

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• Mobile web apps - Is this the right approach?

  - by Pasta

  I need to build a cross platform mobile app (iphone, android, etc). The app is for a company like a cellular operator (Tmobile, ATT). The app needs to do the following: Show previous bills (cached so that it does not have to download everytime) Need an internet connection to download newer bills, view recent data, etc. Can I build a mobile web app to handle this? I understand that there is offline storage and iPhone has good support for web apps (full screen, good icons, offline, etc). Will a web app be the best approach to take as the app requires to be online? The app will not be used by lots of people, just customers of the website who don't want to use an existing website. We are all web developers and a mobile web app looks like the best way to approach this.

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• Using template specialization in C++

  - by user550413

  How can I write a function using template specialization that has 2 different input types and an output type: template <class input1, class input2, class output> and return the sum of the 2 numbers (integers/doubles). However, if I get 2 integers I want to return an integer type but for any other combinations of integer and double I'll always return double. I am trying to do that without using directly the '+' operator but having the next functions instead: double add_double_double(double a, double b) {return (a+b);} double add_int_double(int a, double b) {return ((double)(a)+b);} int add_int_int(int a, int b) {return (a+b);}

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• How does the stream manipulators work?

  - by Narek

  It is well known that the user can define stream manipulators like this: ostream& tab(ostream & output) { return output<< '\t'; } And this can be used in main() like this: cout<<'a'<<tab<<'b'<<'c'<<endl; Please explain me how does this all work? If operator<< assumes as a second parameter a pointer to the function that takes and returns ostream &, then please explain my why it is necessary? What would be wrong if the function does not take and return ostream & but it was void instead of ostream &? Also it is interesting why “dec”, “hex” manipulators take effect until I don’t change between them, but user defined manipulators should be always used in order to take effect for each streaming?

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• What's the simplest way of defining lexicographic comparison for elements of a class?

  - by the_mandrill

  If I have a class that I want to be able to sort (ie support a less-than concept), and it has several data items such that I need to do lexicographic ordering then I need something like this: struct MyData { string surname; string forename; bool operator<(const MyData& other) const { return surname < other.surname || (surname==other.surname && forename < other.forename); } }; This becomes pretty unmanageable for anything with more than 2 data members. Are there any simpler ways of achieving it? The data members may be any Comparable class.

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• What is the difference between "a is b" and "id(a) == id(b)" in Python?

  - by bp

  The id() inbuilt function gives... an integer (or long integer) which is guaranteed to be unique and constant for this object during its lifetime. The is operator, instead, gives... object identity So why is it possible to have two objects that have the same id but return False to an is check? Here is an example: >>> class Test(): ... def test(): ... pass >>> a = Test() >>> b = Test() >>> id(a.test) == id(b.test) True >>> a.test is b.test False A more troubling example: (continuing the above) >>> b = a >>> b is a True >>> b.test is a.test False >>> a.test is a.test False

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• typedef to store pointers in C

  - by seriouslion

  The Size of pointer depends on the arch of the machine. So sizeof(int*)=sizeof(int) or sizeof(int*)=sizeof(long int) I want to have a custom data type which is either int or long int depending on the size of pointer. I tried to use macro #if, but the condition for macros does not allow sizeof operator. Also when using if-else, typedef is limited to the scope of if. if((sizeof(int)==sizeof(int *)){ typedef int ptrtype; } else{ typedef long int ptrtype; } //ptrtype not avialble here Is there any way to define ptrtype globally?

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• BlackBerry - Multiple Screens or Single Screen with Content Manager?

  - by Max Gontar

  Hi! I've seen projects which use many screens each one for different layout and functionality. I've seen projects with only one screen (like wizard workflow) where content is changed on user interaction (and this seems to be logical to use single screen in wizards). But also I've seen projects (apps like game or messenger or phone settings utility) which use single screen for different functionalities. I can see such advantages of having single screen in app: keep same decoration design and menu or toolbar (which may be also achieved with inheritance) keep single screen in ui stack (which may be achieved by pop/push screen) easy to handle data over application Can you tell other advantages/disadvantages of single screen app? When its better to use this approach? Thank you!

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• Django GenericRelation doesn't save related object's id - is this a bug or am I doing it wrong?

  - by pinkeen

  I have a model with a generic relation (call it A), when creating an instance of this object I pass an instance of another model (call it B) as the initializer of the content_object field (via kwargs of the constructor). If I don't save B before creating A then when saving A the content_object_id is saved to the db as NULL. If I save B before passing it to the constructor of A then everything's allright. It's not logical. I assumed that the ID of the related object (B) is fetched when doing A.save() and it should throw some kind of an exception if B isn't saved yet but it just fails silently. I don't like the current solution (saving B beforhand) because we don't know yet if I will be always willing to keep the object, not just scrap it, and there are performance considerations - what if I will add some another data and save it once more shortly after. class BaseNodeData(models.Model): ... extnodedata_content_type = models.ForeignKey(ContentType, null=True) extnodedata_object_id = models.PositiveIntegerField(null=True) extnodedata = generic.GenericForeignKey(ct_field='extnodedata_content_type', fk_field='extnodedata_object_id') class MarkupNodeData(models.Model): raw_content = models.TextField() Suppose we do: markup = MarkupNodeData(raw_content='...') base = BaseNodeData(..., extnodedata=markup) markup.save() base.save() # both records are inserted to the DB but base is stored with extnodedata_object_id=NULL markup = MarkupNodeData(raw_content='...') base = BaseNodeData(..., extnodedata=markup) base.save() markup.save() # no exception is thrown and everything is the same as above markup = MarkupNodeData(raw_content='...') markup.save() base = BaseNodeData(..., extnodedata=markup) base.save() # this works as expected Of course I can do it this way, but it doesn't change anything: base = BaseNodeData(...) base.extnodedata = markup My question is - is this a bug in django which I should report or maybe I'm doing something wrong. Docs on GenericRelations aren't exactly verbose.

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• Changing CCK content-types details results in numerous DB calls for the menu system

  - by Paul Strugger

  Every time I make a change in the details of a content-type it takes too long. I though it had to do with the fact that I had too many content-types and fields (~500), but when I load the devel module to see the queries that take that long I see: Executed 32212 queries in 12267.57 milliseconds. Queries taking longer than 5 ms and queries executed more than once, are highlighted. Page execution time was 55763.32 ms When I see the details I notice that the vast majority of db calls come from the menu system, e.g.: _menu_route menu_local_tasks admin_menu_link_save Why is that? Can I avoid some of these? It doesn't seem logical!

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• Reading function pointer syntax

  - by bobobobo

  Everytime I look at a C function pointer, my eyes glaze over. I can't read them. From here, here are 2 examples of function pointer TYPEDEFS: typedef int (*AddFunc)(int,int); typedef void (*FunctionFunc)(); Now I'm used to something like: typedef vector<int> VectorOfInts ; Which I read as typedef vector<int> /* as */ VectorOfInts ; But I can't read the above 2 typedefs. The bracketing and the asterisk placement, it's just not logical. Why is the * beside the word AddFunc..?

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• Postfix evaluation in C

  - by Andrewziac

  I’m taking a course in C and we have to make a program for the classic Postfix evaluation problem. Now, I’ve already completed this problem in java, so I know that we have to use a stack to push the numbers into, then pop them when we get an operator, I think I’m fine with all of that stuff. The problem I have been having is scanning the postfix expression in C. In java it was easier because you could use charAt and you could use the parseInt command. However, I’m not aware of any similar commands in C. So could anyone explain a method to read each value from a string in the form: 4 9 * 0 - = Where the equals is the signal of the end of the input. Any help would be greatly appreciated and thank you in advance :)

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• Switching from php to python

  - by ts

  Hello I am trying to make a list of things which can be difficult/surprising to someone who is changing language from PHP to Python. so far i have rather short list: forget require / include, learn import (this was most difficult to me - to understand package - module - class - object hierarchy and its mapping to filesystem) you can't just upload file on server to have webpage (-mod_python, wsgi etc) learn the python way for use variable class names (new $class() vs import + getattr) / operator in python 2.x and all float-related horrors those were difficult to me, it takes few days before mind adapts a new paradigm after i found that there is few other areas which could be challenging for someone with (too) many years of php: everything is an object you have to live with exceptions array vs list, set, dictionary, tuple ... learn (effective) list comprehensions learn generators any other ideas / personal experiences ?

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• C++ template specialization

  - by user231536

  I have a class template <typename T> class C { static const int K=1; static ostream& print(ostream& os, const T& t) { return os << t;} }; I would like to specialize C for int. //specialization for int template <> C<int>{ static const int K=2; } I want the default print method that works for int to remain and just change the constant. For some specializations, I want to keep K=1 and change the print method because there is no << operator. How do I do this?

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• binary number comparison

  - by EquinoX

  If I have a 32 bit two's complement number and I want to know what is the easiest way to know of two numbers are equal... what would be the fastest bitwise operator to know this? I know xor'ing both numbers and check if the results are zero works well... any other one's? how about if a number is greater than 0?? I can check the 31'st bit to see if it's greater or equal to 0..but how about bgtz?

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