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• Garbage Collection Java

  - by simion

  On the slides i am revising from it says the following; Live objects can be identified either by maintaining a count of the number of references to each object, or by tracing chains of references from the roots. Reference counting is expensive – it needs action every time a reference changes and it doesn’t spot cyclical structures, but it can reclaim space incrementally. Tracing involves identifying live objects only when you need to reclaim space – moving the cost from general access to the time at which the GC runs, typically only when you are out of memory. I understand the principles of why reference counting is expensive but do not understand what "doesn’t spot cyclical structures, but it can reclaim space incrementally." means. Could anyone help me out a little bit please? Thanks

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• PHP Type Hinting: array supported, object NOT?

  - by Marius Burz

  Am I missing something or there really is no support for generic object type hinting in PHP 5.x? I find it really strange that hinting arrays is supported while hinting objects is not, at least not out of the box. I'd like to have something like this: function foo(object $o) Just as we have: function foo(array $o) Example of possible use: methods of an objects collection class. Workaround: using an interface "Object" implemented by all classes or extending all classes from a generic class "Object" and writing something like this: function foo(Object $o) Well, that just ain't cute. Edit: somebody suggested in a deleted post using stdClass. It doesn't work: Catchable fatal error: Argument 1 passed to c::add() must be an instance of stdClass, instance of b given

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• Is a many-to-many relationship with extra fields the right tool for my job?

  - by whichhand

  Previously had a go at asking a more specific version of this question, but had trouble articulating what my question was. On reflection that made me doubt if my chosen solution was correct for the problem, so this time I will explain the problem and ask if a) I am on the right track and b) if there is a way around my current brick wall. I am currently building a web interface to enable an existing database to be interrogated by (a small number of) users. Sticking with the analogy from the docs, I have models that look something like this: class Musician(models.Model): first_name = models.CharField(max_length=50) last_name = models.CharField(max_length=50) dob = models.DateField() class Album(models.Model): artist = models.ForeignKey(Musician) name = models.CharField(max_length=100) class Instrument(models.Model): artist = models.ForeignKey(Musician) name = models.CharField(max_length=100) Where I have one central table (Musician) and several tables of associated data that are related by either ForeignKey or OneToOneFields. Users interact with the database by creating filtering criteria to select a subset of Musicians based on data the data on the main or related tables. Likewise, the users can then select what piece of data is used to rank results that are presented to them. The results are then viewed initially as a 2 dimensional table with a single row per Musician with selected data fields (or aggregates) in each column. To give you some idea of scale, the database has ~5,000 Musicians with around 20 fields of related data. Up to here is fine and I have a working implementation. However, it is important that I have the ability for a given user to upload there own annotation data sets (more than one) and then filter and order on these in the same way they can with the existing data. The way I had tried to do this was to add the models: class UserDataSets(models.Model): user = models.ForeignKey(User) name = models.CharField(max_length=100) description = models.CharField(max_length=64) results = models.ManyToManyField(Musician, through='UserData') class UserData(models.Model): artist = models.ForeignKey(Musician) dataset = models.ForeignKey(UserDataSets) score = models.IntegerField() class Meta: unique_together = (("artist", "dataset"),) I have a simple upload mechanism enabling users to upload a data set file that consists of 1 to 1 relationship between a Musician and their "score". Within a given user dataset each artist will be unique, but different datasets are independent from each other and will often contain entries for the same musician. This worked fine for displaying the data, starting from a given artist I can do something like this: artist = Musician.objects.get(pk=1) dataset = UserDataSets.objects.get(pk=5) print artist.userdata_set.get(dataset=dataset.pk) However, this approach fell over when I came to implement the filtering and ordering of query set of musicians based on the data contained in a single user data set. For example, I could easily order the query set based on all of the data in the UserData table like this: artists = Musician.objects.all().order_by(userdata__score) But that does not help me order by the results of a given single user dataset. Likewise I need to be able to filter the query set based on the "scores" from different user data sets (eg find all musicians with a score 5 in dataset1 and < 2 in dataset2). Is there a way of doing this, or am I going about the whole thing wrong?

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• Can I add elements to a Java GUI?

  - by Asj

  I want to know how I can make a java program where an unknown amount of objects can be added to a GUI depending on user input. I can program in objects one at a time within the program, but I haven't seen a more dynamic program. Can I do that with Java? If not, what can I do it with? For more information, here's a picture. http://i6.photobucket.com/albums/y223/Asj127/CapProjIdea.jpg There can be more than one question per question block, and each question can have it's own question block.

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• Get/save parameters to an expected JMock method call?

  - by Tayeb

  Hi, I want to test an "Adapter" object that when it receives an xml message, it digest it to a Message object, puts message ID + CorrelationID both with timestamps and forwards it to a Client object.=20 A message can be correlated to a previous one (e.g. m2.correlationID =3D m1.ID). I mock the Client, and check that Adapter successfully calls "client.forwardMessage(m)" twice with first message with null correlationID, and a second with a not-null correlationID. However, I would like to precisely test that the correlationIDs are set correctly, by grabing the IDs (e.g. m1.ID). But I couldn't find anyway to do so. There is a jira about adding the feature, but no one commented and it is unassigned. Is this really unimplemented? I read about the alternative of redesigning the Adapter to use an IdGenerator object, which I can stub, but I think there will be too many objects.=20 Don't you think it adds unnecessary complexity to split objects to a so fine granularity? Thanks, and I appreciate any comments :-) Tayeb

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• a completely decoupled OO system ?

  - by shrini1000

  To make an OO system as decoupled as possible, I'm thinking of the following approach: 1) we run an RMI/directory like service where objects can register and discover each other. They talk to this service through an interface 2) we run a messaging service to which objects can publish messages, and register subscription callbacks. Again, this happens through interfaces 3) when object A wants to invoke a method on object B, it discovers the target object's unique identity through #1 above, and publishes a message on the message service for object B 4) message services invokes B's callback to give it the message 5) B processes the request and sends the response for A on message service 6) A's callback is called and it gets the response. I feel this system is as decoupled as practically possible, but it has the following problems: 1) communication is typically asynchronous 2) hence it's non real time 3) the system as a whole is less efficient. Are there any other practical problems where this design obviously won't be applicable ? What are your thoughts on this design in general ?

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• Architecture of a single-page JavaScript web application?

  - by fig-gnuton

  How should a complex single-page JS web application be structured on the client-side? Specifically I'm curious about how to cleanly structure the application in terms of its model objects, UI components, any controllers, and objects handling server persistence. MVC seemed like a fit at first. But with UI components nested at various depths (each with their own way of acting on/reacting to model data, and each generating events which they themselves may or may not handle directly), it doesn't seem like MVC can be cleanly applied. (But please correct me if that's not the case.) -- (This question resulted in two suggestions of using ajax, which is obviously needed for anything other than the most trivial one-page app.)

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• Query two tables from different schema

  - by Guru

  Hi- I have two different schemas in Oracle (say S1, S2). And two tables in those schemas(say S1.Table1, S2.Table2). I want to query these two tables from schema S1. Both S1 and S2 are in different databases. From DB1 - Schema S1, I want to do something like this, select T1.Id from S1.Table1 T1 , S2.Table2 T2 Where T1.Id = T2.refId I know one way of doing this would be creating a DB Link for the second schema and use it in querying. But sadly, I don't have priv to create DB link. Is there some way to do without DB link, like, in TOAD, you can compare two schema objects. But again, two schema objects and it is general comparision. Not like querying them. Any ideas, suggestions are greatly appriciated. Thanks in advance.

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• Removing Redundant Data from a List<T>

  - by Mark

  I have a List of objects which are ordered. I would like to remove redundant objects where redundant does not necessarily mean duplicate. Here is an example: List<Point> points = new List<Point> { new Point(0, 10), new Point(1, 12), new Point(2, 16), new Point(3, 16), new Point(4, 16), new Point(5, 13), new Point(6, 16), }; I am interested in removing the new Point(3, 16) entry because it doesn't provide useful information; I already know that the element at 2=16 and the element at 4=16. The information that 3=16 doesn't do me any good in my application (because I already have the bounds {2,4}=16), so I would like to remove that entry. I'd also like to not that I want to keep the 5th and 6th entry because there are not consecutive entries where Y=16. Is there a slick way to do this with linq?

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• Can I change class types in a setter with an object-oriented language?

  - by user214626

  Hello, Here is the problem statement : Calling a setter on the object should result in the object to change to an object of a different class, which language can support this ? Ex. I have a class called "Man" (Parent Class), and two children namely "Toddler" and "Old Man", they are its children because they override a behaviour in Man called as walk.( i.e Toddler sometimes walks using both his hands and legs kneeled down and the Old man uses a stick to support himself). The Man class has a attribute called age, I have a setter on Man,say it is called setAge(int ageValue). I have 3 objects, 2 toddlers, 1 old-Man. (The system is up and running,i guess when we say objects it is obvious) .I will make this call, toddler.setAge(80), I expect the toddler to change to an object of type Old Man. Is this possible.Please suggest. Thanks,

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• Create new vsftpd user and lock to (specify) home / login directory

  - by Geoff Jackson

  I need to periodically give temporary and limited access to various directories on a CentOS linux server that has vsftp installed. I've created a user using useradd [user_name] and given them a password using passwd [password]. I've created a directory in /var/ftp and then I bind this to the directory that I wish to limit access to. What else do I need to specifically do to ensure that when this user logs into FTP, they only have access to this directory please?

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• Plotting a cumulative graph of python datetimes

  - by ventolin

  Say I have a list of datetimes, and we know each datetime to be the recorded time of an event happening. Is it possible in matplotlib to graph the frequency of this event occuring over time, showing this data in a cumulative graph (so that each point is greater or equal to all of the points that went before it), without preprocessing this list? (e.g. passing datetime objects directly to some wonderful matplotlib function) Or do I need to turn this list of datetimes into a list of dictionary items, such as: {"year": 1998, "month": 12, "date": 15, "events": 92} and then generate a graph from this list? Sorry if this seems like a silly question - I'm not all too familiar with matplotlib, and would like to save myself the effort of doing this the latter way if matplotlib can already deal with datetime objects itself.

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• Multiple operations depending on the type of the object passed

  - by mixm

  Assuming I create a method which is passed an object and that method would perform an action depending on the object passed. How should I identify the object? I thought of using the class name to identify the object, but that may be impractical since I could easily change the class name of objects, and generate headaches during future development. Am I right? edit: for example, i have objects ball and bomb. if i have another object called wall, and the wall has the method to resolve collisions with the wall (e.g. the coordinates of the colliding ball and bomb) but have different logic depending on the colliding object (i.e. ball and bomb)

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• Twisted Spread: How to authenticate each RPC with digital signature

  - by kronat

  I have remote objects which talk each others with RPCs, using Twisted Spread. I want that objects authenticate messages, before using them, with digital signatures, but I don't know where to start to implement this. In my head, the Root object must have a public/private key pair, and the Client too. When a message is sent, a digital signature of the hash is added, and when it is received, the signature is checked. Is the Protocol part where I need to add these adds and checks? Thank you

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• ProtoBuffers, sending the protoobjects over the network

  - by Faisal Abid

  My webservice(in java) will generate ProtoBuffer objects, how do i send this across so that my Python script can read the protobuffer object?

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• Spring + Hibernate session management

  - by toc777

  I have been reading about using Spring with Hibernate and I am really confused about session management. Hopefully someone can clear a few things up for me, First of all I have no idea how sessions are managed when using HibernateTemplate. Is a session opened and closed when you call a method Eg Save() on the template? When you use the find() method, are detached objects returned? I have read the Spring section on transactions but it mostly talks about handling exceptions. I was hoping to find some way of binding a hibernate session to a Spring transaction so that I can commit changes to hibernate objects when the transaction finishes. Is there a way to achieve this?

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• Is an ArrayList automaticaly declared static in Java, if it is an instance variable?

  - by Alex

  I'm trying to do something like this: private class aClass { private ArrayList<String> idProd; aClass(ArrayList<String> prd) { this.idProd=new ArrayList<String>(prd); } public ArrayList<String> getIdProd() { return this.idProd; } } So if I have multiple instances of ArrayLIst<String> (st1 ,st2 ,st3) and I want to make new objects of aClass: { aClass obj1,obj2,obj3; obj1=new aClass(st1); obj2=new aClass(st2); obj3=new aClass(st3); } Will all of the aClass objects return st3 if I access the method getIdProd() for each of them(obj1..obj3)? Is an ArrayList as an instance variable automatically declared static?

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• Is an ArrayList automatically declared static in Java, if it is an instance variable?

  - by Alex

  I'm trying to do something like this: private class aClass { private ArrayList<String> idProd; aClass(ArrayList<String> prd) { this.idProd=new ArrayList<String>(prd); } public ArrayList<String> getIdProd() { return this.idProd; } } So if I have multiple instances of ArrayLIst<String> (st1 ,st2 ,st3) and I want to make new objects of aClass: { aClass obj1,obj2,obj3; obj1=new aClass(st1); obj2=new aClass(st2); obj3=new aClass(st3); } Will all of the aClass objects return st3 if I access the method getIdProd() for each of them(obj1..obj3)? Is an ArrayList as an instance variable automatically declared static?

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• Building a world matrix

  - by DeadMG

  When building a world projection matrix from scale, rotate, translate matrices, then the translation matrix must be the last in the process, right? Else you'll be scaling or rotating your translations. Do scale and rotate need to go in a specific order? Right now I've got std::for_each(objects.begin(), objects.end(), [&, this](D3D93DObject* ptr) { D3DXMATRIX WVP; D3DXMATRIX translation, rotationX, rotationY, rotationZ, scale; D3DXMatrixTranslation(&translation, ptr->position.x, ptr->position.y, ptr->position.z); D3DXMatrixRotationX(&rotationX, ptr->rotation.x); D3DXMatrixRotationY(&rotationY, ptr->rotation.y); D3DXMatrixRotationZ(&rotationZ, ptr->rotation.z); D3DXMatrixScaling(&translation, ptr->scale.x, ptr->scale.y, ptr->scale.z); WVP = rotationX * rotationY * rotationZ * scale * translation * ViewProjectionMatrix; });

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• Unit Testing - Am I doing it right?

  - by baron

  Hi everyone, Basically I have been programing for a little while and after finishing my last project can fully understand how much easier it would have been if I'd have done TDD. I guess I'm still not doing it strictly as I am still writing code then writing a test for it, I don't quite get how the test becomes before the code if you don't know what structures and how your storing data etc... but anyway... Kind of hard to explain but basically lets say for example I have a Fruit objects with properties like id, color and cost. (All stored in textfile ignore completely any database logic etc) FruitID FruitName FruitColor FruitCost 1 Apple Red 1.2 2 Apple Green 1.4 3 Apple HalfHalf 1.5 This is all just for example. But lets say I have this is a collection of Fruit (it's a List<Fruit>) objects in this structure. And my logic will say to reorder the fruitids in the collection if a fruit is deleted (this is just how the solution needs to be). E.g. if 1 is deleted, object 2 takes fruit id 1, object 3 takes fruit id2. Now I want to test the code ive written which does the reordering, etc. How can I set this up to do the test? Here is where I've got so far. Basically I have fruitManager class with all the methods, like deletefruit, etc. It has the list usually but Ive changed hte method to test it so that it accepts a list, and the info on the fruit to delete, then returns the list. Unit-testing wise: Am I basically doing this the right way, or have I got the wrong idea? and then I test deleting different valued objects / datasets to ensure method is working properly. [Test] public void DeleteFruit() { var fruitList = CreateFruitList(); var fm = new FruitManager(); var resultList = fm.DeleteFruitTest("Apple", 2, fruitList); //Assert that fruitobject with x properties is not in list ? how } private static List<Fruit> CreateFruitList() { //Build test data var f01 = new Fruit {Name = "Apple",Id = 1, etc...}; var f02 = new Fruit {Name = "Apple",Id = 2, etc...}; var f03 = new Fruit {Name = "Apple",Id = 3, etc...}; var fruitList = new List<Fruit> {f01, f02, f03}; return fruitList; }

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• Writing secure java code with RMI

  - by jtnire

  Hi Everyone, This may seem like a very broad question, but any help is appreciated. I have a client/server solution written in java which uses the Cajo project (which uses RMI). I just want to try and make my solution as secure as possible, given the sensitive data that will be transferred between server and client. So far, my ideas are to make all my classes "final" as well as throw a "non-serializable" exception for all my classes in the server (except for the object bound in the RMI registry, and any objects that actually do need to be transferred of course). Can anyone think of any other ideas? I know that someone could write a malicious client - this isn't hard to do as you can find out the remote object's API using reflection. However is there anything I can do to protect a malicious client access classes/objects within the server that they are not supposed to access? Many Thanks

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• How to access this server?

  - by George Edison

  I have a server that I cannot access. At first I thought it was just some temporary failure with the server, but checking from other IP addresses reveals that it is working just fine. It's only my IP address that's failing. So here is what I've tried: nslookup - resolves correctly ping - 100% packet loss using the IP address or domain traceroute - first few hops work, but from about 6 and on, I just get stars Edit: I am using OpenDNS for DNS resolution, and as mentioned above, the problem is not DNS resolution anyway.

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• MVC Routes - How to get a URL?

  - by Seattle Leonard

  In my current project we have a notification system. When an oject is added to another objects collection, an email is sent to those who are subscibed to the parent object. This happens on the object layer and not in the View or Controller. Here's the problem: Although we can say who created what with what information in the email, we cannot embed links to those objects in the email because in the object layer there is no access to a UrlHelper. To construct a UrlHelper you need a RequestContext, which again does not exist on the object layer. Question: I want to make a helper class to create the url's for me. How can I create an object that will generate these urls without a request context? Is it possible?

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• C++ containers on classes, returning pointers

  - by otneil

  Hello, I'm having some trouble to find the best way to accomplish what I have in mind due to my inexperience. I have a class where I need to a vector of objects. So my first question will be: is there any problem having this: vector< AnyType container* and then on the constructor initialize it with new (and deleting it on the destructor)? Another question is: if this vector is going to store objects, shouldn't it be more like vector< AnyTipe* so they could be dynamically created? In that case how would I return an object from a method and how to avoid memory leaks (trying to use only STL)?

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• Looking for design patterns to isolate framework layers from each other

  - by T Reddy

  Hi, I'm wondering if anyone has any experience in "isolating" framework objects from each other (Spring, Hibernate, Struts). I'm beginning to see design "problems" where an object from one framework gets used in another object from a different framework. My fear is we're creating tightly coupled objects. For instance, I have an application where we have a DynaActionForm with several attributes...one of which is a POJO generated by the Hibernate Tools. This POJO gets used everywhere...the JSP populates data to it, the Struts Action sends it down to a Service Layer, the DAO will persist it...ack! Now, imagine that someone decides to do a little refactoring on that POJO...so that means the JSP, Action, Service, DAO all needs to be updated...which is kind of painful...There has got to be a better way?! There's a book called Core J2EE Patterns: Best Practices and Design Strategies (2nd Edition)...is this worth a look? I don't believe it touches on any specific frameworks, but it looks like it might give some insight on how to properly layer the application... Thanks!

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