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  • regarding object recycling

    - by ajaycv
    I have a question. What is wrong with regards to the below code: ArrayList tempList2 = new ArrayList(); tempList2 = getXYZ(tempList1, tempList2); //method getXYZ getXYZ(ArrayList tempList1, ArrayList tempList2) { //does some logic and adds objects into tempList2 return tempList2; } The code will get executed but it seems by passing tempList2 to the getXYZ method argument, it is doing object recycling. My question is, Is recycling the tempList2 arraylist object correct?

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  • saveOrUpdate(Object) method of Hibernate

    - by Vikram
    when i use saveOrUpdate(Object) method of Hibernate. How can I know that row is updated or new row added into table??? Return type of method saveOrUpdate(Object) is void, so am not able to find out the result after calling this method. kindly help me.

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  • notation of Path to files/folders/drives that is shared on a network in windows?

    - by claws
    Hello, When some thing shared on network using windows network share option. Some people use path like \\something\something\something$ I'm don't know if this is correct way or not. but as far as I remember there is a dollar sign. Can any one please tell me. What is this notation? Where can I find more details about this? What is samba server/sharing? I don't understand when people use it. Is it something related to Linux? EDIT I'm a programmer. I guess this file sharing on network using windows uses client server architecture. I want to know what is this server on windows called? What protocol does it use? client is of course our windows explorer.exe? Which service in services.msc is responsible for this?

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  • Android: problem retrieving bitmap from database

    - by Addy
    When I'm retrieving image from the sqlite database my Bitmap object bm return null value can any one help me..? I found problem in my database.. When I store the byte array in blob data type in database table that time the size of the byte array was 2280.. But when i retrieved that blob data type using select query I get the byte array within size 12. My code is: // Inserting data in database byte[] b; ByteArrayOutputStream baos = new ByteArrayOutputStream(); Bitmap bm = BitmapFactory.decodeResource(getResources(),R.drawable.icon); bm.compress(Bitmap.CompressFormat.PNG, 100, baos); //bm is the bitmap object b = baos.toByteArray(); //here b size is 2280 baos.close(); try { mDB = this.openOrCreateDatabase(MY_DATABASE_NAME, MODE_PRIVATE, null); mDB.execSQL("CREATE TABLE IF NOT EXISTS " + MY_DATABASE_TABLE + " (PICTURE BLOB);"); mDB.execSQL("INSERT INTO " + MY_DATABASE_TABLE + " (PICTURE)" + " VALUES ('"+b+"');"); } catch(Exception e) { Log.e("Error", "Error", e); } finally { if(mDB != null) mDB.close(); } // Retriving data from database byte[] b1; Bitmap bm; mDB = this.openOrCreateDatabase(MY_DATABASE_NAME, MODE_PRIVATE, null); try { mDB.execSQL("CREATE TABLE IF NOT EXISTS " + MY_DATABASE_TABLE + " (PICTURE BLOB);"); Cursor c = mDB.rawQuery("SELECT * FROM " + MY_DATABASE_TABLE + ";", null); c.moveToFirst(); if (c != null) { do { b1=c.getBlob(0)); //here b1 size is 12 bm=BitmapFactory.decodeByteArray(b1, 0, b1.length); }while(c.moveToNext()); }

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  • How to marshall non-string objects with JAXB and Spring

    - by lesula
    I was trying to follow this tutorial in order to create my own restful web-service using Spring framework. The client do a GET request to, let's say http://api.myapp/app/students and the server returns an xml version of the object classroom: @XmlRootElement(name = "class") public class Classroom { private String classId = null; private ArrayList<Student> students = null; public Classroom() { } public String getClassId() { return classId; } public void setClassId(String classId) { this.classId = classId; } @XmlElement(name="student") public ArrayList<Student> getStudents() { return students; } public void setStudents(ArrayList<Student> students) { this.students = students; } } The object Student is another bean containing only Strings. In my app-servlet.xml i copied this lines: <bean id="studentsView" class="org.springframework.web.servlet.view.xml.MarshallingView"> <constructor-arg ref="jaxbMarshaller" /> </bean> <!-- JAXB2 marshaller. Automagically turns beans into xml --> <bean id="jaxbMarshaller" class="org.springframework.oxm.jaxb.Jaxb2Marshaller"> <property name="classesToBeBound"> <list> <value>com.spring.datasource.Classroom</value> <value>com.spring.datasource.Student</value> </list> </property> </bean> Now my question is: what if i wanted to insert some non-string objects as class variables? Let's say i want a tag containing the String version of an InetAddress, such as <inetAddress>192.168.1.1</inetAddress> How can i force JAXB to call the method inetAddress.toString() in such a way that it appears as a String in the xml? In the returned xml non-string objects are ignored!

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  • USE case to Class Diagram - How do I?

    - by 01010011
    Hi, I would like your guidance on how to create classes and their relationships (generalization, association, aggregation and composition) accurately from my USE case diagram (please see below). I am trying to create this class diagram so I can use it to create a simple online PHP application that allows the user to register an account, login and logout, and store, search and retrieve data from a MySQL database. Are my classes correct? Or should I create more classes? And if so, what classes are missing? What relationships should I use when connecting the register, login, logout, search_database and add_to_database to the users? I'm new to design patterns and UML class diagrams but from my understanding, the association relationship relates one object with another object; the aggregation relationship is a special kind of association that allows "a part" to belong to more than one "whole" (e.g. a credit card and its PIN - the PIN class can also be used in a debit card class); and a composition relationship is a special form of aggregation that allows each part to belong to only one whole at a time. I feel like I have left out some classes or something because I just can't seem to find the relationships from my understanding of relationships. Any assistance will be really appreciated. Thanks in advance. USE CASE DIAGRAM CLASS DIAGRAM

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  • Doubts About Core Data NSManagedObject Deep Copy

    - by Jigzat
    Hello everyone, I have a situation where I must copy one NSManagedObject from the main context into an editing context. It sounds unnecessary to most people as I have seen in similar situations described in Stackoverflow but I looks like I need it. In my app there are many views in a tab bar and every view handles different information that is related to the other views. I think I need multiple MOCs since the user may jump from tab to tab and leave unsaved changes in some tab but maybe it saves data in some other tab/view so if that happens the changes in the rest of the views are saved without user consent and in the worst case scenario makes the app crash. For adding new information I got away by using an adding MOC and then merging changes in both MOCs but for editing is not that easy. I saw a similar situation here in Stackoverflow but the app crashes since my data model doesn't seem to use NSMutableSet for the relationships (I don't think I have a many-to-many relationship, just one-to-many) I think it can be modified so I can retrieve the relationships as if they were attributes for (NSString *attr in relationships) { [cloned setValue:[source valueForKey:attr] forKey:attr]; } but I don't know how to merge the changes of the cloned and original objects. I think I could just delete the object from the main context, then merge both contexts and save changes in the main context but I don't know if is the right way to do it. I'm also concerned about database integrity since I'm not sure that the inverse relationships will keep the same reference to the cloned object as if it were the original one. Can some one please enlighten me about this?

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  • Writing fortran robust and "modern" code

    - by Blklight
    In some scientific environments, you often cannot go without FORTRAN as most of the developers only know that idiom, and there is lot of legacy code and related experience. And frankly, there are not many other cross-platform options for high performance programming ( C++ would do the task, but the syntax, zero-starting arrays, and pointers are too much for most engineers ;-) ). I'm a C++ guy but I'm stuck with some F90 projects. So, let's assume a new project must use FORTRAN (F90), but I want to build the most modern software architecture out of it. while being compatible with most "recent" compilers (intel ifort, but also including sun/HP/IBM own compilers) So I'm thinking of imposing: global variable forbidden, no gotos, no jump labels, "implicit none", etc. "object-oriented programming" (modules with datatypes + related subroutines) modular/reusable functions, well documented, reusable libraries assertions/preconditions/invariants (implemented using preprocessor statements) unit tests for all (most) subroutines and "objects" an intense "debug mode" (#ifdef DEBUG) with more checks and all possible Intel compiler checks possible (array bounds, subroutine interfaces, etc.) uniform and enforced legible coding style, using code processing tools C stubs/wrappers for libpthread, libDL (and eventually GPU kernels, etc.) C/C++ implementation of utility functions (strings, file operations, sockets, memory alloc/dealloc reference counting for debug mode, etc.) ( This may all seem "evident" modern programming assumptions, but in a legacy fortran world, most of these are big changes in the typical programmer workflow ) The goal with all that is to have trustworthy, maintainable and modular code. Whereas, in typical fortran, modularity is often not a primary goal, and code is trustworthy only if the original developer was very clever, and the code was not changed since then ! (i'm a bit joking here, but not much) I searched around for references about object-oriented fortran, programming-by-contract (assertions/preconditions/etc.), and found only ugly and outdated documents, syntaxes and papers done by people with no large-scale project involvement, and dead projects. Any good URL, advice, reference paper/books on the subject?

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  • Converting a pointer for a base class into an inherited class

    - by Shawn B
    Hey, I'm working on a small roguelike game, and for any object/"thing" that is not a part of the map is based off an XEntity class. There are several classes that depend on it, such as XPlayer, XItem, and XMonster. My problem is, that I want to convert a pointer from XEntity to XItem when I know that an object is in item. The sample code I am using to pick up an item is this, it is when a different entity picks up an item it is standing over. void XEntity::PickupItem() { XEntity *Ent = MapList; // Start of a linked list while(true) { if(Ent == NULL) { break; } if(Ent->Flags & ENT_ITEM) { Ent->RemoveEntity(); // Unlink from the map's linked list XItem *Item = Ent // Problem is here, type-safety // Code to link into inventory is here break; } Ent = Ent->MapList; } } My first thought was to create a method in XEntity that returns itself as an XItem pointer, but it creates circular dependencies that are unresolvable. I'm pretty stumped about this one. Any help is greatly appreciated.

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  • Using a Javascript Variable & Sending to JSON

    - by D Franks
    Hello all! I'm trying to take a URL's hash value, send it through a function, turn that value into an object, but ultimately send the value to JSON. I have the following setup: function content(cur){ var mycur = $H(cur); var pars = "p="+mycur.toJSON(); new Ajax.Updater('my_box', 'test.php', { parameters: pars }); } function update(){ if(window.location.hash.length > 0){ content(window.location.hash.substr(1)); // Everything after the '#' } } var curHashVal = window.location.hash; window.onload = function(){ setInterval(function(){ if(curHashVal != window.location.hash){ update(); curHashVal = window.location.hash; } },1); } But for some reason, I can't seem to get the right JSON output. It will either return as a very large object (1:"{",2:"k") or not return at all. I doubt that it is impossible to accomplish, but I've exhausted most of the ways I can think of. Other ways I've tried were "{" + cur + "}" as well as cur.toObject(), however, none seemed to get the job done. Thanks for the help!

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  • jQuery add() function and the context of jQuery objects

    - by patrick
    Given the following HTML example... <div id='div1'>div one</div> <div id='div2'>div two</div> ...I found that the following jQuery code... $('#div1').click(function() { var $d = $(this); // Using 'this' instead of '#div1' $d.add('#div2').remove(); }); ...would not add #div2 to the set referenced by $d, but this code... $('#div1').click(function() { var $d = $('#div1'); // Using '#div1' instead of 'this' $d.add('#div2').remove(); }); ...successfully added #div2. Upon consulting firebug, I found that using $(this) gave the jQuery object a context of #div1, but doing $('#div1') gave the object a context of document. Given this information I tried... var $d = $(this, document); ...and the add() function worked as expected. So here's the question. Could someone please explain to my why a different context is assigned when using $(this) vs $('#div1')? Thanks much!

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  • Python: saving and loading objects and using pickle.

    - by Peterstone
    Hello, I´m trying to save and load objects using pickle module. First I declare my objects: >>> class Fruits:pass ... >>> banana = Fruits() >>> banana.color = 'yellow' >>> banana.value = 30 After that I open a file called 'Fruits.obj'(previously I created a new .txt file and I renamed 'Fruits.obj'): >>> import pickle >>> filehandler = open(b"Fruits.obj","wb") >>> pickle.dump(banana,filehandler) After do this I close my session and I began a new one and I put the next (trying to access to the object that it supposed to be saved): file = open("Fruits.obj",'r') object_file = pickle.load(file) But I have this message: Traceback (most recent call last): File "<stdin>", line 1, in <module> File "C:\Python31\lib\pickle.py", line 1365, in load encoding=encoding, errors=errors).load() ValueError: read() from the underlying stream did notreturn bytes I don´t know what to do because I don´t understand this message. Does anyone know How I can load my object 'banana'? Thank you! EDIT: As some of you have sugested I put: >>> import pickle >>> file = open("Fruits.obj",'rb') There were no problem, but the next I put was: >>> object_file = pickle.load(file) And I have error: Traceback (most recent call last): File "<stdin>", line 1, in <module> File "C:\Python31\lib\pickle.py", line 1365, in load encoding=encoding, errors=errors).load() EOFError

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  • Simply doing modelType.ToString() isn't sufficient, How can i use it via Activator.CreateInstance?

    - by programmerist
    public class MyController { public object CreateByEnum(DataModelType modeltype) { string enumText = modeltype.ToString(); // will return for example "Company" Type classType = Type.GetType(enumText); // the Type for Company class object t = Activator.CreateInstance(classType); // create an instance of Company class return t; } } public class CompanyView { public static List<Personel> GetPersonel() { MyController controller = new MyController(); _Company company = controller.CreateByEnum(DataModelType.Company) as _Company; return company.GetPersonel(); } } public enum DataModelType { xyz, klm, tucyz, Company } Yes, I agree Activator.CreateInstance() is very useful. Unfortunately, I need to pass in the correct type. That means building the correct string to pass to Type.GetType(). If I trace through the call to Controller.CreatebyEnum() in the code I posted above, simply doing modelType.ToString() isn't sufficient, even for the case of DataModelType.Company. My solution'll be maintenance bottleneck. What would be better is something that takes the results of modelType.ToString() and then recursively searches through all the types found in all the assemblies loaded in the current AppDomain. According to MSDN, Type.GetType() only searches the current calling assembly, and mscorlib.dll. How can i do that? . i need best performance?

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  • What is the best way to store site configuration data?

    - by DaveDev
    I have a question about storing site configuration data. We have a platform for web applications. The idea is that different clients can have their data hosted and displayed on their own site which sits on top of this platform. Each site has a configuration which determines which panels relevant to the client appear on which pages. The system was originally designed to keep all the configuration data for each site in a database. When the site is loaded all the configuration data is loaded into a SiteConfiguration object, and the clients panels are generated based on the content of this object. This works, but I find it very difficult to work with to apply change requests or add new sites because there is so much data to sift through and it's difficult maintain a mental model of the site and its configuration. Recently I've been tasked with developing a subset of some of the sites to be generated as PDF documents for printing. I decided to take a different approach to how I would define the configuration in that instead of storing configuration data in the database, I wrote XML files to contain the data. I find it much easier to work with because instead of reading meaningless rows of data which are related to other meaningless rows of data, I have meaningful documents with semantic, readable information with the relationships defined by visually understandable element nesting. So now with these 2 approaches to storing site configuration data, I'd like to get the opinions of people more experienced in dealing with this issue on dealing with these two approaches. What is the best way of storing site configuration data? Is there a better way than the two ways I outlined here? note: StackOverflow is telling me the question appears to be subjective and is likely to be closed. I'm not trying to be subjective. I'd like to know how best to approach this issue next time and if people with industry experience on this could provide some input.

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  • Setting up relations/mappings for a SQLAlchemy many-to-many database

    - by Brent Ramerth
    I'm new to SQLAlchemy and relational databases, and I'm trying to set up a model for an annotated lexicon. I want to support an arbitrary number of key-value annotations for the words which can be added or removed at runtime. Since there will be a lot of repetition in the names of the keys, I don't want to use this solution directly, although the code is similar. My design has word objects and property objects. The words and properties are stored in separate tables with a property_values table that links the two. Here's the code: from sqlalchemy import Column, Integer, String, Table, create_engine from sqlalchemy import MetaData, ForeignKey from sqlalchemy.orm import relation, mapper, sessionmaker from sqlalchemy.ext.declarative import declarative_base engine = create_engine('sqlite:///test.db', echo=True) meta = MetaData(bind=engine) property_values = Table('property_values', meta, Column('word_id', Integer, ForeignKey('words.id')), Column('property_id', Integer, ForeignKey('properties.id')), Column('value', String(20)) ) words = Table('words', meta, Column('id', Integer, primary_key=True), Column('name', String(20)), Column('freq', Integer) ) properties = Table('properties', meta, Column('id', Integer, primary_key=True), Column('name', String(20), nullable=False, unique=True) ) meta.create_all() class Word(object): def __init__(self, name, freq=1): self.name = name self.freq = freq class Property(object): def __init__(self, name): self.name = name mapper(Property, properties) Now I'd like to be able to do the following: Session = sessionmaker(bind=engine) s = Session() word = Word('foo', 42) word['bar'] = 'yes' # or word.bar = 'yes' ? s.add(word) s.commit() Ideally this should add 1|foo|42 to the words table, add 1|bar to the properties table, and add 1|1|yes to the property_values table. However, I don't have the right mappings and relations in place to make this happen. I get the sense from reading the documentation at http://www.sqlalchemy.org/docs/05/mappers.html#association-pattern that I want to use an association proxy or something of that sort here, but the syntax is unclear to me. I experimented with this: mapper(Word, words, properties={ 'properties': relation(Property, secondary=property_values) }) but this mapper only fills in the foreign key values, and I need to fill in the other value as well. Any assistance would be greatly appreciated.

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  • Using pointers to adjust global objects in objective-c

    - by Rob
    Ok, so I am working with two sets of data that are extremely similar, and at the same time, these data sets are both global NSMutableArrays within the object. data_set_one = [[NSMutableArray alloc] init]; data_set_two = [[NSMutableArray alloc] init]; Two new NSMutableArrays are loaded, which need to be added to the old, existing data. These Arrays are also global. xml_dataset_one = [[NSMutableArray alloc] init]; xml_dataset_two = [[NSMutableArray alloc] init]; To reduce code duplication (and because these data sets are so similar) I wrote a void method within the class to handle the data combination process for both Arrays: -(void)constructData:(NSMutableArray *)data fromDownloadArray:(NSMutableArray *)down withMatchSelector:(NSString *)sel_str Now, I have a decent understanding of object oriented programming, so I was thinking that if I were to invoke the method with the global Arrays in the data like so... [self constructData:data_set_one fromDownloadArray:xml_dataset_one withMatchSelector:@"id"]; Then the global NSMutableArrays (data_set_one) would reflect the changes that happen to "array" within the method. Sadly, this is not the case, data_set_one doesn't reflect the changes (ex: new objects within the Array) outside of the method. Here is a code snippet of the problem // data_set_one is empty // xml_dataset_one has a few objects [constructData:(NSMutableArray *)data_set_one fromDownloadArray:(NSMutableArray *)xml_dataset_one withMatchSelector:(NSString *)@"id"]; // data_set_one should now be xml_dataset_one, but when echoed to screen, it appears to remain empty And here is the gist of the code for the method, any help is appreciated. -(void)constructData:(NSMutableArray *)data fromDownloadArray:(NSMutableArray *)down withMatchSelector:(NSString *)sel_str { if ([data count] == 0) { data = down; // set data equal to downloaded data } else if ([down count] == 0) { // download yields no results, do nothing } else { // combine the two arrays here } } This project is not ARC enabled. Thanks for the help guys! Rob

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  • Flex DataGridColumn with array of objects as data provider

    - by rforte
    I have a datagrid that uses an array of objects as the data provider. The objects are essentially key/value pairs: { foo:"something"} { bar:"hello"} { caca:"lorem"} The datagrid has 2 columns. The first column is the key and the second column is the value. Right now my grid looks like: My dataFormatter function makes sure that depending on the column (i.e. the dataField value) the correct key or value gets printed out. This works fine for displaying. However, as soon as I try and edit the value field it essentially adds a new value into the object with a key of '1'. For example, if I edit the {caca:"lorem"} object it will then contain the value {caca:"lorem",1:"new value"}. Is there any possible way I can set the DataGridColumn so that when I edit a value it will update the value associated with the key rather than inserting a new value? I've tried using a custom item editor but it still does the insert. It seems like I need to be able to update the 'dataField' with the actual key value but I'm not sure how to do that.

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  • When is factory method better than simple factory and vice versa?

    - by Bruce
    Hi all Working my way through the Head First Design Patterns book. I believe I understand the simple factory and the factory method, but I'm having trouble seeing what advantages factory method brings over simple factory. If an object A uses a simple factory to create its B objects, then clients can create it like this: A a = new A(new BFactory()); whereas if an object uses a factory method, a client can create it like this: A a = new ConcreteA(); // ConcreteA contains a method for instantiating the same Bs that the BFactory above creates, with the method hardwired into the subclass of A, ConcreteA. So in the case of the simple factory, clients compose A with a B factory, whereas with the factory method, the client chooses the appropriate subclass for the types of B it wants. There really doesn't seem to be much to choose between them. Either you have to choose which BFactory you want to compose A with, or you have to choose the right subclass of A to give you the Bs. Under what circumstances is one better than the other? Thanks all!

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  • Python: Errors saving and loading objects with pickle module

    - by Peterstone
    Hi, I am trying to load and save objects with this piece of code I get it from a question I asked a week ago: Python: saving and loading objects and using pickle. The piece of code is this: class Fruits: pass banana = Fruits() banana.color = 'yellow' banana.value = 30 import pickle filehandler = open("Fruits.obj","wb") pickle.dump(banana,filehandler) filehandler.close() file = open("Fruits.obj",'rb') object_file = pickle.load(file) file.close() print(object_file.color, object_file.value, sep=', ') At a first glance the piece of code works well, getting load and see the 'color' and 'value' of the saved object. But, what I pursuit is to close a session, open a new one and load what I save in a past session. I close the session after putting the line filehandler.close() and I open a new one and I put the rest of your code, then after putting object_file = pickle.load(file) I get this error: Traceback (most recent call last): File "<pyshell#5>", line 1, in <module> object_file = pickle.load(file) File "C:\Python31\lib\pickle.py", line 1365, in load encoding=encoding, errors=errors).load() AttributeError: 'module' object has no attribute 'Fruits' Can anyone explain me what this error message means and telling me how to solve this problem? Thank so much and happy new year!!

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  • Alternatives to static methods on interfaces for enforcing consistency

    - by jayshao
    In Java, I'd like to be able to define marker interfaces, that forced implementations to provide static methods. For example, for simple text-serialization/deserialization I'd like to be able to define an interface that looked something like this: public interface TextTransformable<T>{ public static T fromText(String text); public String toText(); Since interfaces in Java can't contain static methods though (as noted in a number of other posts/threads: here, here, and here this code doesn't work. What I'm looking for however is some reasonable paradigm to express the same intent, namely symmetric methods, one of which is static, and enforced by the compiler. Right now the best we can come up with is some kind of static factory object or generic factory, neither of which is really satisfactory. Note: in our case our primary use-case is we have many, many "value-object" types - enums, or other objects that have a limited number of values, typically carry no state beyond their value, and which we parse/de-parse thousands of time a second, so actually do care about reusing instances (like Float, Integer, etc.) and its impact on memory consumption/g.c. Any thoughts?

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  • How to display video on html page in firefox

    - by Manish
    I did looked at this question, but the asker didn't got any reply. Still, I'm giving it a try. I want to embed a video file on a html page. The code works fine on IE but doesn't work on firefox. The code: <object id="WMPlay" width="640" height="480" classid="CLSID:6BF52A52-394A-11d3-B153-00C04F79FAA6" codebase="http://activex.microsoft.com/activex/controls/mplayer/en/nsmp2inf.cab#Version=5,1,52,70" standby="Loading Microsoft Windows Media Player components..." type="application/x-oleobject"> <param name="URL" value="XYZ.wma" /> <param name="AutoStart" value="false" /> <embed name="WMplay" width="640" height="480" type="application/x-mplayer2" pluginspage="http://www.microsoft.com/Windows/Downloads/Contents/Products/MediaPlayer/" src="XYZ.wma" allowchangedisplaysize="True" showcontrols="1" autostart="false" showdisplay="1" showstatusbar="1"> </embed> </object> Can someone please tell what am I missing? Or a better solution..something which is browser independent... :)

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  • C++ Matrix class hierachy

    - by bpw1621
    Should a matrix software library have a root class (e.g., MatrixBase) from which more specialized (or more constrained) matrix classes (e.g., SparseMatrix, UpperTriangluarMatrix, etc.) derive? If so, should the derived classes be derived publicly/protectively/privately? If not, should they be composed with a implementation class encapsulating common functionality and be otherwise unrelated? Something else? I was having a conversation about this with a software developer colleague (I am not per se) who mentioned that it is a common programming design mistake to derive a more restricted class from a more general one (e.g., he used the example of how it was not a good idea to derive a Circle class from an Ellipse class as similar to the matrix design issue) even when it is true that a SparseMatrix "IS A" MatrixBase. The interface presented by both the base and derived classes should be the same for basic operations; for specialized operations, a derived class would have additional functionality that might not be possible to implement for an arbitrary MatrixBase object. For example, we can compute the cholesky decomposition only for a PositiveDefiniteMatrix class object; however, multiplication by a scalar should work the same way for both the base and derived classes. Also, even if the underlying data storage implementation differs the operator()(int,int) should work as expected for any type of matrix class. I have started looking at a few open-source matrix libraries and it appears like this is kind of a mixed bag (or maybe I'm looking at a mixed bag of libraries). I am planning on helping out with a refactoring of a math library where this has been a point of contention and I'd like to have opinions (that is unless there really is an objective right answer to this question) as to what design philosophy would be best and what are the pros and cons to any reasonable approach.

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