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• What is the better design decision approach?

  - by palm snow

  I have two classes (MyFoo1 and MyFoo2) that share some common functionality. So far it does not seem like I need any polymorphic inheritence but at this point I am considering the following options: Have the common functionality in a utility class. Both of these classes call these methods from that utility class. Have an abstract class and implement common methods in that abstract class. Then derive MyFoo1 and MyFoo2 from that abstract class. Any suggestion on what would be a better design decision?

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• Advice on approaching a significant rearrangement/refactoring?

  - by Prog

  I'm working on an application (hobby project, solo programmer, small-medium size), and I have recently redesigned a significant part of it. The program already works in it's current state, but I decided to reimplement things to improve the OO design. I'm about to implement this new design by refactoring a big part of the application. Thing is I'm not sure where to start. Obviously, by the nature of a rearrangement, the moment you change one part of the program several other parts (at least temporarily) break. So it's a little 'scary' to rearrange something in a piece of software that already works. I'm asking for advice or some general guidelines: how should I approach a significant refactoring? When you approach rearranging large parts of your application, where do you start? Note that I'm interested only in re-arranging the high-level structure of the app. I have no intention of rewriting local algorithms.

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• "Collection Wrapper" pattern - is this common?

  - by Prog

  A different question of mine had to do with encapsulating member data structures inside classes. In order to understand this question better please read that question and look at the approach discussed. One of the guys who answered that question said that the approach is good, but if I understood him correctly - he said that there should be a class existing just for the purpose of wrapping the collection, instead of an ordinary class offering a number of public methods just to access the member collection. For example, instead of this: class SomeClass{ // downright exposing the concrete collection. Things[] someCollection; // other stuff omitted Thing[] getCollection(){return someCollection;} } Or this: class SomeClass{ // encapsulating the collection, but inflating the class' public interface. Thing[] someCollection; // class functionality omitted. public Thing getThing(int index){ return someCollection[index]; } public int getSize(){ return someCollection.length; } public void setThing(int index, Thing thing){ someCollection[index] = thing; } public void removeThing(int index){ someCollection[index] = null; } } We'll have this: // encapsulating the collection - in a different class, dedicated to this. class SomeClass{ CollectionWrapper someCollection; CollectionWrapper getCollection(){return someCollection;} } class CollectionWrapper{ Thing[] someCollection; public Thing getThing(int index){ return someCollection[index]; } public int getSize(){ return someCollection.length; } public void setThing(int index, Thing thing){ someCollection[index] = thing; } public void removeThing(int index){ someCollection[index] = null; } } This way, the inner data structure in SomeClass can change without affecting client code, and without forcing SomeClass to offer a lot of public methods just to access the inner collection. CollectionWrapper does this instead. E.g. if the collection changes from an array to a List, the internal implementation of CollectionWrapper changes, but client code stays the same. Also, the CollectionWrapper can hide certain things from the client code - from example, it can disallow mutation to the collection by not having the methods setThing and removeThing. This approach to decoupling client code from the concrete data structure seems IMHO pretty good. Is this approach common? What are it's downfalls? Is this used in practice?

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• Should the 12-String be in it's own class and why?

  - by MayNotBe

  This question is regarding a homework project in my first Java programming class (online program). The assignment is to create a "stringed instrument" class using (among other things) an array of String names representing instrument string names ("A", "E", etc). The idea for the 12-string is beyond the scope of the assignment (it doesn't have to be included at all) but now that I've thought of it, I want to figure out how to make it work. Part of me feels like the 12-String should have it's own class, but another part of me feels that it should be in the guitar class because it's a guitar. I suppose this will become clear as I progress but I thought I would see what kind of response I get here. Also, why would they ask for a String[] for the instrument string names? Seems like a char[] makes more sense. Thank you for any insight. Here's my code so far (it's a work in progress): public class Guitar { private int numberOfStrings = 6; private static int numberOfGuitars = 0; private String[] stringNotes = {"E", "A", "D", "G", "B", "A"}; private boolean tuned = false; private boolean playing = false; public Guitar(){ numberOfGuitars++; } public Guitar(boolean twelveString){ if(twelveString){ stringNotes[0] = "E, E"; stringNotes[1] = "A, A"; stringNotes[2] = "D, D"; stringNotes[3] = "G, G"; stringNotes[4] = "B, B"; stringNotes[5] = "E, E"; numberOfStrings = 12; } } public int getNumberOfStrings() { return numberOfStrings; } public void setNumberOfStrings(int strings) { if(strings == 12 || strings == 6) { if(strings == 12){ stringNotes[0] = "E, E"; stringNotes[1] = "A, A"; stringNotes[2] = "D, D"; stringNotes[3] = "G, G"; stringNotes[4] = "B, B"; stringNotes[5] = "E, E"; numberOfStrings = strings; } if(strings == 6) numberOfStrings = strings; }//if else System.out.println("***ERROR***Guitar can only have 6 or 12 strings***ERROR***"); } public void getStringNotes() { for(int i = 0; i < stringNotes.length; i++){ if(i == stringNotes.length - 1) System.out.println(stringNotes[i]); else System.out.print(stringNotes[i] + ", "); }//for }

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• Should Equality be commutative within a Class Hierachy?

  - by vossad01

  It is easy to define the Equals operation in ways that are not commutative. When providing equality against other types, there are obviously situations (in most languages) were equality not being commutative is unavoidable. However, within one's own inheritance hierarchy where the root base class defines an equality member, a programmer has more control. Thus you can create situations where (A = B) ? (B = A), where A and B both derive from base class T Substituting the = with the appropriate variation for a given language. (.Equals(_), ==, etc.) That seems wrong to me, however, I recognize I may be biased by background in Mathematics. I have not been in programming long enough to know what is standard/accepted/preferred practice when programming. Do most programmers just accept .Equals(_)may not be commutative and code defensibly. Do they expect commutativity and get annoyed if it is not. In short, when working in a class hierarchy, should effort me made to ensure Equality is commutative?

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• How should I refactor switch statements like this (Switching on type) to be more OO?

  - by Taytay

  I'm seeing some code like this in our code base, and want to refactor it: (Typescript psuedocode follows): class EntityManager{ private findEntityForServerObject(entityType:string, serverObject:any):IEntity { var existingEntity:IEntity = null; switch(entityType) { case Types.UserSetting: existingEntity = this.getUserSettingByUserIdAndSettingName(serverObject.user_id, serverObject.setting_name); break; case Types.Bar: existingEntity = this.getBarByUserIdAndId(serverObject.user_id, serverObject.id); break; //Lots more case statements here... } return existingEntity; } } The downsides of switching on type are self-explanatory. Normally, when switching behavior based on type, I try to push the behavior into subclasses so that I can reduce this to a single method call, and let polymorphism take care of the rest. However, the following two things are giving me pause: 1) I don't want to couple the serverObject with the class that is storing all of these objects. It doesn't know where to look for entities of a certain type. And unfortunately, the identity of a type of ServerObject varies with the type of ServerObject. (So sometimes it's just an ID, other times it's a combination of an id and a uniquely identifying string, etc). And this behavior doesn't belong down there on those subclasses. It is the responsibility of the EntityManager and its delegates. 2) In this case, I can't modify the ServerObject classes since they're plain old data objects. It should be mentioned that I've got other instances of the above method that take a parameter like "IEntity" and proceed to do almost the same thing (but slightly modify the name of the methods they're calling to get the identity of the entity). So, we might have: case Types.Bar: existingEntity = this.getBarByUserIdAndId(entity.getUserId(), entity.getId()); break; So in that case, I can change the entity interface and subclasses, but this isn't behavior that belongs in that class. So, I think that points me to some sort of map. So eventually I will call: private findEntityForServerObject(entityType:string, serverObject:any):IEntity { return aMapOfSomeSort[entityType].findByServerObject(serverObject); } private findEntityForEntity(someEntity:IEntity):IEntity { return aMapOfSomeSort[someEntity.entityType].findByEntity(someEntity); } Which means I need to register some sort of strategy classes/functions at runtime with this map. And again, I darn well better remember to register one for each my my types, or I'll get a runtime exception. Is there a better way to refactor this? I feel like I'm missing something really obvious here.

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• Did Bjarne Stroustrup create the terms constructor/destructor when talking about objects?

  - by user104971

  I was watching this keynote and Bjarne Stroustrup (Creator of C++) claims that he hadn't yet invented the words constructor and destructor yet when he was giving an example of RAII. http://www.youtube.com/watch?v=IYBLXBJr0HU I know the concept of construction and destruction has been around a lot longer (even in C, a function that allocates and returns a struct and then a function that frees it etc.), but was Bjarne really the first to invent the terms?

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• Deleting a game object

  - by Balls

  I tried doing this but it cause an access violation. void GameObjectFactory::Update() { for( std::list<GameObject*>::iterator it=gameObjectList.begin() ..... (*it)->Update(); } void Bomb::Update() { if( time == 2.0f ) { gameObjectFactory->Remove( this ); } } void GameObjectFactory::Remove( ... ) { gameObjectList.remove( ... ); } My thoughts would be to mark the object to be dead then let the factory handle it the on next frame for deletion. Is it the best and fastest way? What do you think?

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• Should the 12-String be in it's own class and why? Java

  - by MayNotBe

  This is my first question here. I will amend it as instructed. This is regarding a homework project in my first Java programming class (online program). The assignment is to create a "stringed instrument" class using (among other things) an array of String names representing instrument string names ("A", "E", etc). The idea for the 12-string is beyond the scope of the assignment (it doesn't have to be included at all) but now that I've thought of it, I want to figure out how to make it work. Part of me feels like the 12-String should have it's own class, but another part of me feels that it should be in the guitar class because it's a guitar. I suppose this will become clear as I progress but I thought I would see what kind of response I get here. Also, why would they ask for a String[] for the instrument string names? Seems like a char[] makes more sense. Thank you for any insight. Here's my code so far (it's a work in progress): public class Guitar { private int numberOfStrings = 6; private static int numberOfGuitars = 0; private String[] stringNotes = {"E", "A", "D", "G", "B", "A"}; private boolean tuned = false; private boolean playing = false; public Guitar(){ numberOfGuitars++; } public Guitar(boolean twelveString){ if(twelveString){ stringNotes[0] = "E, E"; stringNotes[1] = "A, A"; stringNotes[2] = "D, D"; stringNotes[3] = "G, G"; stringNotes[4] = "B, B"; stringNotes[5] = "E, E"; numberOfStrings = 12; } } public int getNumberOfStrings() { return numberOfStrings; } public void setNumberOfStrings(int strings) { if(strings == 12 || strings == 6) { if(strings == 12){ stringNotes[0] = "E, E"; stringNotes[1] = "A, A"; stringNotes[2] = "D, D"; stringNotes[3] = "G, G"; stringNotes[4] = "B, B"; stringNotes[5] = "E, E"; numberOfStrings = strings; } if(strings == 6) numberOfStrings = strings; }//if else System.out.println("***ERROR***Guitar can only have 6 or 12 strings***ERROR***"); } public void getStringNotes() { for(int i = 0; i < stringNotes.length; i++){ if(i == stringNotes.length - 1) System.out.println(stringNotes[i]); else System.out.print(stringNotes[i] + ", "); }//for }

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• A programmer who doesn't get to program - where to turn? [closed]

  - by Just an Anon

  I'm in my mid 20's, and have been working as a full time programmer / developer for the last ~6 years, with several years of part-time freelancing before this, and three straight years of freelancing in the middle of this short career. I work mostly with PHP and the Drupal framework. By and large, I focus on programming custom pieces of functionality; these, of course, vary greatly from project to project. I've got years of solid experience with OOP (have done some Java & C# years ago, too) including intensive experience with front-end development, and even some design work. I've lead small teams (2-4 people) of developers. And of course, given the large amount of freelancing, I've got decent project- & client-management skills. My problem is staying motivated at any place of employment. In the time mentioned I've worked (full-time) at six local companies. The longest I've stayed at any company was just over a year. I find that I'll get hired and be very excited and motivated for the first few months, but the work quickly gets "stale." By that I mean that the interesting components (ie. the programming) get done, and the rest of the work turns into boring cleanup (move a button, add text, change colours, add a field). I don't get challenged, and I don't feel like I'm learning anything new. This happens repeatedly time and time again, and I always end up leaving for either a new opportunity, or to freelance. I'm wondering if perhaps I've painted myself into a corner with the rather niche work market (although with very high demand and good compensation) and need to explore other career choices. Another possibility is that I may be choosing the wrong places of employment, mostly small agencies, and need to look into working for a larger, more established firm. I find programming, writing code, and architecting solutions very rewarding. When I'm working on an interesting problem I lose all sense of time and 14-16 hours can fly by like minutes. I get the same exciting feeling when I'm doing high-level planning of a complex system, breaking up the work and figuring out how everything will tie-in together. I absolutely hate doing small, "stupid" changes that pose no challenge, yet seem to make up more and more of my work. I want to find a workplace where I will get to work on such tasks, be challenged, and improve in all areas of product development. This maybe a programming job, management, architecture of desktop apps, or may be managing a taco stand on a beach in Mexico - I don't know, and I need some advice and real-world feedback. What are some job areas worth exploring? The requirements are fairly simple: working with computers interacting with others challenging decent pay (I'm making just short of 90k / year with a month of vacation & some benefits, and would like to stay in this range, but am willing to take a temporary cut in pay for a more interesting position) Any advice would be much appreciated!

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• PHP class data implementation

  - by Bakanyaka

  I'm studying OOP PHP and have watched two tutorials that implement user login\registration system as an example. But implementation varies. Which way will be more correct one to work with data such as this? Load all data retrieved from database as array into a property called something like _data on class creation and further methods operate with this property Create separate properties for each field retrieved from database, on class creation load all data fields into respective properties and operate with that properties separately? Then let's say I want to create a method that returns a list of all users with their data. Which way is better? Method that returns just an array of userdata like this: Array([0]=>array([id] => 1, [username] => 'John', ...), [1]=>array([id] => 2, [username] => 'Jack', ...), ...) Method that creates a new instance of it's class for each user and returns an array of objects

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• Multiple parameters vs single parameter(object with multiple properties)

  - by Shwetanka

  I have an Entity Student with following properties - (name, joinedOn, birthday, age, batch, etc.) and a function fetchStudents(<params>). I want to fetch students based on multiple filters. In my method I have two ways to pass filters. Pass all filters as params to the method Make a class StudentCriteria with filters as fields and then pass the object of this class While working in java I always go with the second option but recently I'm working in php and I was advised to go with the first way. I am unable to figure out which way is better in maintaining the code, reusability and performance wise. Thanks.

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• IXRepository and test problems

  - by Ridermansb

  Recently had a doubt about how and where to test repository methods. Let the following situation: I have an interface IRepository like this: public interface IRepository<T> where T: class, IEntity { IQueryable<T> Query(Expression<Func<T, bool>> expression); // ... Omitted } And a generic implementation of IRepository public class Repository<T> : IRepository<T> where T : class, IEntity { public IQueryable<T> Query(Expression<Func<T, bool>> expression) { return All().Where(expression).AsQueryable(); } } This is an implementation base that can be used by any repository. It contains the basic implementation of my ORM. Some repositories have specific filters, in which case we will IEmployeeRepository with a specific filter: public interface IEmployeeRepository : IRepository<Employee> { IQueryable<Employee> GetInactiveEmployees(); } And the implementation of IEmployeeRepository: public class EmployeeRepository : Repository<Employee>, IEmployeeRepository // TODO: I have a dependency with ORM at this point in Repository<Employee>. How to solve? How to test the GetInactiveEmployees method { public IQueryable<Employee> GetInactiveEmployees() { return Query(p => p.Status != StatusEmployeeEnum.Active || p.StartDate < DateTime.Now); } } Questions Is right to inherit Repository<Employee>? The goal is to reuse code once all implementing IRepository already been made. If EmployeeRepository inherit only IEmployeeRepository, I have to literally copy and paste the code of Repository<T>. In our example, in EmployeeRepository : Repository<Employee> our Repository lies in our ORM layer. We have a dependency here with our ORM impossible to perform some unit test. How to create a unit test to ensure that the filter GetInactiveEmployees return all Employees in which the Status != Active and StartDate < DateTime.Now. I can not create a Fake/Mock of IEmployeeRepository because I would be testing? Need to test the actual implementation of GetInactiveEmployees. The complete code can be found on Github

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• Is "If a method is re-used without changes, put the method in a base class, else create an interface" a good rule-of-thumb?

  - by exizt

  A colleague of mine came up with a rule-of-thumb for choosing between creating a base class or an interface. He says: Imagine every new method that you are about to implement. For each of them, consider this: will this method be implemented by more than one class in exactly this form, without any change? If the answer is "yes", create a base class. In every other situation, create an interface. For example: Consider the classes cat and dog, which extend the class mammal and have a single method pet(). We then add the class alligator, which doesn't extend anything and has a single method slither(). Now, we want to add an eat() method to all of them. If the implementation of eat() method will be exactly the same for cat, dog and alligator, we should create a base class (let's say, animal), which implements this method. However, if it's implementation in alligator differs in the slightest way, we should create an IEat interface and make mammal and alligator implement it. He insists that this method covers all cases, but it seems like over-simplification to me. Is it worth following this rule-of-thumb?

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• Android app, No error message but has stopped unexpectedly [migrated]

  - by user74722

  Does anyone know what is my problem. I do not have any compile error messages however when i run the app it crashes and stops unexpectedly. Here is my codes. Thank you in advance. ListView l ; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_final_project); String arr[]={"Red","Green","Blue","Yellow","Cyan"}; l=(ListView) findViewById(R.id.listView1); ArrayAdapter<String> adapter=new ArrayAdapter<String>(getApplicationContext(), android.R.layout.simple_list_item_1, arr); l.setAdapter(adapter); Button buttonOne = (Button) findViewById(R.id.button1); buttonOne.setOnClickListener(new OnClickListener(){ @Override public void onClick(View v){ setContentView(R.layout.layout_save); // setContentView(R.layout.activity_final_project); //startActivity(new Intent("com.example.finalproject.layout_save")); } }); }

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• Vertex Array Object (OpenGL)

  - by user5140

  I've just started out with OpenGL I still haven't really understood what Vertex Array Objects are and how they can be employed. If Vertex Buffer Object are used to store vertex data (such as their positions and texture coordinates) and the VAOs only contain status flags, where can they be used? What's their purpose? As far as I understood from the (very incomplete and unclear) GL Wiki, VAOs are used to set the flags/status for every vertex, following the order described in the Element Array Buffer, but the wiki was really ambiguous about it and I'm not really sure about what VAOs really do and how I could employ them.

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• Which order to define getters and setters in? [closed]

  - by N.N.

  Is there a best practice for the order to define getters and setters in? There seems to be two practices: getter/setter pairs first getters, then setters (or the other way around) To illuminate the difference here is a Java example of getter/setter pairs: public class Foo { private int var1, var2, var3; public int getVar1() { return var1; } public void setVar1(int var1) { this.var1 = var1; } public int getVar2() { return var2; } public void setVar2(int var2) { this.var2 = var2; } public int getVar3() { return var3; } public void setVar3(int var3) { this.var3 = var3; } } And here is a Java example of first getters, then setters: public class Foo { private int var1, var2, var3; public int getVar1() { return var1; } public int getVar2() { return var2; } public int getVar3() { return var3; } public void setVar1(int var1) { this.var1 = var1; } public void setVar2(int var2) { this.var2 = var2; } public void setVar3(int var3) { this.var3 = var3; } } I think the latter type of ordering is clearer both in code and in class diagrams but I do not know if that is enough to rule out the other type of ordering.

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• [PHP] Making a good singleton registry class structure which hold your objects

  - by Saif Bechan

  I am working on a web application in PHP. I have a singleton class called registry. This class will hold all the objects i need throughout my application, such as loader classes, template classes, database, classes, etc. When an object of the registry class is created I send it an array with the classes it need to load: // Create the registry $registry = registry::singleton(); // Store those core objects $registry->storeObjects(Array('session','db','page','template','errors')); In this example I only put some of the classes, to get the basic idea. Now I have some classes in the registry that use each other. For example the 'errors' object uses the 'page' object. Now I was wondering if it is a good practice to make an instance of the registry object in the errors object. Like this; class errors{ private $registry; public function __construct(){ $this->registry = registry::singleton(); } } So there is an instance of the registry object, inside an object of the registry object. This does not sound like a good idea to me. Anyone have a suggestion how to model such a thing?

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• Javascript "this" variable confusion

  - by Assaf M

  Hi I am currently reading the book "Javascript: The Good Parts" and was playing with Functions. I produced a test script to test some properties and I am somewhat confused by the results. Here is the code: <h3>Object</h3> <div style="padding-left: 10px;"> <script type="text/javascript"> function outterF() { document.writeln("outterF.this = " + this + "<br>"); function innerF() { document.writeln("innerF.this = " + this + "<br>"); return this; }; var inner = innerF(); return this; } document.writeln("<b>From Inside:</b><br>"); var outF = outterF(); var inF = outF.inner; document.writeln("<br>"); document.writeln("<b>From Outside:</b><br>"); document.writeln("outterF.this = " + outF + "<br>"); document.writeln("innerF.this = " + inF + "<br>"); </script> </div> Result is: Object From Inside: outterF.this = [object Window] innerF.this = [object Window] From Outside: outterF.this = [object Window] innerF.this = undefined Notice that outF.inner returns "undefined", is that some kind of a language bug? Obviously, outF.inner points to Window object that has nothing to do with my object but shouldn't it be at least pointing to a Function object instead? Thanks -Assaf

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• C# - Calling ToString() on a Reference Type

  - by nfplee

  Given two object arrays I need to compare the differences between the two (when converted to a string). I've reduced the code to the following and the problem still exists: public void Compare(object[] array1, object[] array2) { for (var i = 0; i < array1.Length; i++) { var value1 = GetStringValue(array1[i]); var value2 = GetStringValue(array2[i]); } } public string GetStringValue(object value) { return value != null && value.ToString() != string.Empty ? value.ToString() : ""; } The code executes fine no matter what object arrays I throw at it. However if one of the items in the array is a reference type then somehow the reference is updated. This causes issues later. It appears that this happens when calling ToString() against the object reference. I have updated the GetStringValue method to the following (which makes sure the object is either a value type or string) and the problem goes away. public string GetStringValue(object value) { return value != null && (value.GetType().IsValueType || value is string) && value.ToString() != string.Empty ? value.ToString() : ""; } However this is just a temporary hack as I'd like to be able to override the ToString() method on my reference types and compare them as well. I'd appreciate it if someone could explain why this is happening and offer a potential solution. Thanks

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• Java: Comparing a class with another within that class using a my own .equals

  - by user1670252

  I am making a method .equals replacing the equals method used. It accepts a object. I want it to check if that object equals the class that runs the .equals class. I know I want to compare all the private methods I have to that object. Is there a way to do this without making another private class to get the private variables from the object? How do I do this to compare equality not identity? I am stuck on this. Do i have to use == to compare? Also looking online i see others use recursion. If this is the way i have to do it can you show and explain it to me? so an example i have public boolean equals(Object o) { this is in a class we will call bobtheBuilder (first thing to pop in my head) I want to check if the object o is equal to the class he has private object array and a private int. I assume I want to check if the array and int of this class equal the array and int of the object.

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• Not seeing Sync Block in Object Layout

  - by bob-bedell

  It's my understanding the all .NET object instances begin with an 8 byte 'object header': a synch block (4 byte pointer into a SynchTableEntry table), and a type handle (4 byte pointer into the types method table). I'm not seeing this in VS 2010 RC's (CLR 4.0) debugger memory windows. Here's a simple class that will generate a 16 byte instance, less the object header. class Program { short myInt = 2; // 4 bytes long myLong = 3; // 8 bytes string myString = "aString"; // 4 byte object reference // 16 byte instance static void Main(string[] args) { new Program(); return; } } An SOS object dump tells me that the total object size is 24 bytes. That makes sense. My 16 byte instance plus an 8 byte object header. !DumpObj 0205b660 Name: Offset_Test.Program MethodTable: 000d383c EEClass: 000d13f8 Size: 24(0x18) bytes File: C:\Users\Bob\Desktop\Offset_Test\Offset_Test\bin\Debug\Offset_Test.exe Fields: MT Field Offset Type VT Attr Value Name 632020fc 4000001 10 System.Int16 1 instance 2 myInt 632050d8 4000002 4 System.Int64 1 instance 3 myLong 631fd2b8 4000003 c System.String 0 instance 0205b678 myString Here's the raw memory: 0x0205B660 000d383c 00000003 00000000 0205b678 00000002 ... And here are some annotations: offset 0 000d383c ;TypeHandle (pointer to MethodTable), 4 bytes offset 4 00000003 00000000 ;myLong, 8 bytes offset 12 0205b678 ;myString, 4 byte reference to address of "myString" on GC Heap offset 16 00000002 ;myInt, 4 bytes My object begins a address 0x0205B660. But I can only account for 20 bytes of it, the type handle and the instance fields. There is no sign of a synch block pointer. The object size is reported as 24 bytes, but the debugger is showing that it only occupies 20 bytes of memory. I'm reading Drill Into .NET Framework Internals to See How the CLR Creates Runtime Objects, and expected the first 4 bytes of my object to be a zeroed synch block pointer, as shown in Figure 8 of that article. Granted, this is an article about CLR 1.1. I'm just wondering if the difference between what I'm seeing and what this early article reports is a change in either the debugger's display of object layout, or in the way the CLR lays out objects in versions later than 1.1. Anyway, can anyone account for my 4 missing bytes?

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• Xenserver 5.5 U2 a bit unstable with an unstable W2003 VM

  - by twistedbrain

  In the last week I had to reboot the host system twice and the second one by means of the power button. The system is a Dell PE 6950 (4 Opteron dual core, 2,8 Ghz, 16 GB RAM, 900 GB disk in a RAID 10 array composed by 4 450GB 15000 rpm disks) with XenServer 5.5 U2. We're installing it and at now there are working in production a 2003 32 bit Windows server VM with 2 GB RAM, 3 vcpu and about 200 GB disk in 4 partition (12 GB boot, 20 GB program, 80 GB user data, 80 GB other data). The first time I was compressing many Windows 2003 folders (some tens GB by means of W2003 compressed folder option) from a Windows remote console and some hours before my colleague installed Backup Exec agent that was alredy installed and that required a reboot (that was pending). The console stopped responding, it was no more possible to connect by means of remote console or by means of the console of the XenCentre, it was still possible from the network to use the shared folder of the VM and the programs on it (2 db and a GIS program), but the print server didn't work any more and I couldn't give remote reboot from other domain controller hosts. I couldn't stop the virtual machine neither from the XenCentre, neither from the command line of the host also forcing the reboot. I had to reboot the host server. Yesterday it has been worst. I installed a template of another VM, CentOS 5.3 and then, put the DVD in the drive of the host. Then, before the install and after the boot I checked for defect the DVD and the W2003 VM began to respond slowly (I was connected by means of an administration remote console) the task manager showed only mid or low load, it is, only the first of the 3 vcpu was loaded (about 70%), while the other two were about at 20% and also the disk I/O was not so heavy. Then the users were not so happy because they couldn't any more use the MS word docs on the server. I immediately stopped the check of the DVD (to do that I had to force the stop of such Centos 5.3 VM), then some users could again use their docs, but other had still problems, so I decided to reboot the VM, but it doesn't stopped, neither from XenCenter, neither from command line, neither forcing the reboot. Then I tried to reboot of the host, but it didn't worked, neither from the XenCentre, neither from the host prompt (shutdown -r now as root: it told that it was shutting down, but then it didn't did that). So I had to power off by means of the power button of the server (before I tried some Magic SyS REQ, but I saw that Xen isn't compiled with this option enabled). What could you suggest about my problem, what can I look, search and see? In the W2003 VM logs there are no errors or warning to explain what happened. Some more exciting, amusing and inspiring words of poetry (the facts happened around 11 am): \# egrep -i 'err|warning' xensource.log [20100219 10:32:05.597|debug|culo|6301 unix-RPC|VBD.plug R:c81bcda701f6|xenops] watch: watching xenstore paths: [ /xapi/0/frontend/vbd/51712/hotplug; /local/domain/0/backend/vbd/0/51712/tapdisk-error ] with timeout 1200.000000 seconds [20100219 10:32:05.597|debug|culo|6301 unix-RPC|VBD.plug R:c81bcda701f6|xenops] watch: fired on /local/domain/0/backend/vbd/0/51712/tapdisk-error [20100219 10:32:14.314|debug|culo|6335 unix-RPC|VBD.unplug R:9258f54578d6|xenops] watch: watching xenstore paths: [ /local/domain/0/backend/vbd/0/51712/shutdown-done; /local/domain/0/error/device/vbd/51712/error ] with timeout 1200.000000 seconds [20100219 10:32:14.337|debug|culo|6335 unix-RPC|VBD.unplug R:9258f54578d6|xenops] xenstore-rm /local/domain/0/error/backend/vbd/0 [20100219 10:32:14.337|debug|culo|6335 unix-RPC|VBD.unplug R:9258f54578d6|xenops] xenstore-rm /local/domain/0/error/device/vbd/51712 [20100219 10:32:14.338|debug|culo|6335 unix-RPC|VBD.unplug R:9258f54578d6|xenops] watch: fired on /local/domain/0/error/device/vbd/51712/error [20100219 10:53:48.903|debug|culo|6418|Async.VM.hard_shutdown R:88d2095678f7|helpers] Ignoring exception: INTERNAL_ERROR: [ Xb.Noent ] while Vmops.destroy_domain: Destroying domid 14 guest session [20100219 10:53:52.048|debug|culo|6418|Async.VM.hard_shutdown R:88d2095678f7|xenops] xenstore-rm /local/domain/0/error/backend/tap/14 [20100219 10:53:52.048|debug|culo|6418|Async.VM.hard_shutdown R:88d2095678f7|xenops] xenstore-rm /local/domain/14/error/device/vbd/51744 [20100219 10:53:52.085|debug|culo|6418|Async.VM.hard_shutdown R:88d2095678f7|xenops] xenstore-rm /local/domain/0/error/backend/tap/14 [20100219 10:53:52.086|debug|culo|6418|Async.VM.hard_shutdown R:88d2095678f7|xenops] xenstore-rm /local/domain/14/error/device/vbd/51728 [20100219 10:53:52.122|debug|culo|6418|Async.VM.hard_shutdown R:88d2095678f7|xenops] xenstore-rm /local/domain/0/error/backend/tap/14 [20100219 10:53:52.122|debug|culo|6418|Async.VM.hard_shutdown R:88d2095678f7|xenops] xenstore-rm /local/domain/14/error/device/vbd/51712 [20100219 10:53:52.127|debug|culo|6418|Async.VM.hard_shutdown R:88d2095678f7|xenops] xenstore-rm /local/domain/0/error/backend/vbd/14 [20100219 10:53:52.128|debug|culo|6418|Async.VM.hard_shutdown R:88d2095678f7|xenops] xenstore-rm /local/domain/14/error/device/vbd/51760 [20100219 10:53:52.496|debug|culo|6418|Async.VM.hard_shutdown R:88d2095678f7|xenops] Device.Vif.hard_shutdown about to blow away backend and error paths [20100219 10:53:52.497|debug|culo|6418|Async.VM.hard_shutdown R:88d2095678f7|xenops] xenstore-rm /local/domain/0/error/backend/vif/14 [20100219 10:53:52.497|debug|culo|6418|Async.VM.hard_shutdown R:88d2095678f7|xenops] xenstore-rm /local/domain/14/error/device/vif/0 [20100219 10:53:53.385|debug|culo|6418|Async.VM.hard_shutdown R:88d2095678f7|xenops] Device.Vif.hard_shutdown about to blow away backend and error paths [20100219 10:53:53.386|debug|culo|6418|Async.VM.hard_shutdown R:88d2095678f7|xenops] xenstore-rm /local/domain/0/error/backend/vif/14 [20100219 10:53:53.386|debug|culo|6418|Async.VM.hard_shutdown R:88d2095678f7|xenops] xenstore-rm /local/domain/14/error/device/vif/1 [20100219 10:53:53.389| warn|culo|6418|Async.VM.hard_shutdown R:88d2095678f7|hotplug] Warning, deleting 'vif' entry from /xapi/14/hotplug/vif/0 [20100219 10:53:53.391| warn|culo|6418|Async.VM.hard_shutdown R:88d2095678f7|hotplug] Warning, deleting 'vif' entry from /xapi/14/hotplug/vif/1 [20100219 11:20:49.766|debug|culo|6484|Async.VM.clean_shutdown R:78d3c3e28cb6|helpers] Ignoring exception: INTERNAL_ERROR: [ Xb.Noent ] while Vmops.destroy_domain: Destroying domid 11 guest session [20100219 11:20:50.339|debug|culo|6484|Async.VM.clean_shutdown R:78d3c3e28cb6|xenops] xenstore-rm /local/domain/0/error/backend/tap/11 [20100219 11:20:50.339|debug|culo|6484|Async.VM.clean_shutdown R:78d3c3e28cb6|xenops] xenstore-rm /local/domain/11/error/device/vbd/832 [20100219 11:20:50.360|debug|culo|6484|Async.VM.clean_shutdown R:78d3c3e28cb6|xenops] xenstore-rm /local/domain/0/error/backend/tap/11 [20100219 11:20:50.360|debug|culo|6484|Async.VM.clean_shutdown R:78d3c3e28cb6|xenops] xenstore-rm /local/domain/11/error/device/vbd/768 [20100219 11:20:50.366|debug|culo|6484|Async.VM.clean_shutdown R:78d3c3e28cb6|xenops] xenstore-rm /local/domain/0/error/backend/vbd/11 [20100219 11:20:50.366|debug|culo|6484|Async.VM.clean_shutdown R:78d3c3e28cb6|xenops] xenstore-rm /local/domain/11/error/device/vbd/5696 [20100219 11:20:50.753|debug|culo|6484|Async.VM.clean_shutdown R:78d3c3e28cb6|xenops] Device.Vif.hard_shutdown about to blow away backend and error paths [20100219 11:20:50.754|debug|culo|6484|Async.VM.clean_shutdown R:78d3c3e28cb6|xenops] xenstore-rm /local/domain/0/error/backend/vif/11 [20100219 11:20:50.754|debug|culo|6484|Async.VM.clean_shutdown R:78d3c3e28cb6|xenops] xenstore-rm /local/domain/11/error/device/vif/1 [20100219 11:20:50.757| warn|culo|6484|Async.VM.clean_shutdown R:78d3c3e28cb6|hotplug] Warning, deleting 'vif' entry from /xapi/11/hotplug/vif/1 [20100219 11:28:13.803|debug|culo|6610 inet-RPC|Connection to VM console R:e9f8b76e8975|console] error: INTERNAL_ERROR: [ Unix.Unix_error(63, "connect", "") ]

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• Grails - Removing an item from a hasMany association List on data bind?

  - by ecrane

  Grails offers the ability to automatically create and bind domain objects to a hasMany List, as described in the grails user guide. So, for example, if my domain object "Author" has a List of many "Book" objects, I could create and bind these using the following markup (from the user guide): <g:textField name="books[0].title" value="the Stand" /> <g:textField name="books[1].title" value="the Shining" /> <g:textField name="books[2].title" value="Red Madder" /> In this case, if any of the books specified don't already exist, Grails will create them and set their titles appropriately. If there are already books in the specified indices, their titles will be updated and they will be saved. My question is: is there some easy way to tell Grails to remove one of those books from the 'books' association on data bind? The most obvious way to do this would be to omit the form element that corresponds to the domain instance you want to delete; unfortunately, this does not work, as per the user guide: Then Grails will automatically create a new instance for you at the defined position. If you "skipped" a few elements in the middle ... Then Grails will automatically create instances in between. I realize that a specific solution could be engineered as part of a command object, or as part of a particular controller- however, the need for this functionality appears repeatedly throughout my application, across multiple domain objects and for associations of many different types of objects. A general solution, therefore, would be ideal. Does anyone know if there is something like this included in Grails?

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• Core Data managed object context thread synchronisation

  - by Ben Reeves

  I'm have an issue where i'm updating a many-to-many relationship in a background thread, which works fine in that threa, but when I send the object back to the main thread the changes do not show. If I close the app and reopen the data is saved fine and the changes show on the main thread. Also using [context lock] instead of a different managed object context works fine. I have tried NSManagedObjectContext: - (BOOL)save:(NSError **)error; - (void)refreshObject:(NSManagedObject *)object mergeChanges:(BOOL)flag; at different stages throughout the process but it doesn't seem to help. My core data code uses the following getter to ensure any operations are thread safe: - (NSManagedObjectContext *) managedObjectContext { NSThread * thisThread = [NSThread currentThread]; if (thisThread == [NSThread mainThread]) { //Main thread just return default context return managedObjectContext; } else { //Thread safe trickery NSManagedObjectContext * threadManagedObjectContext = [[thisThread threadDictionary] objectForKey:CONTEXT_KEY]; if (threadManagedObjectContext == nil) { threadManagedObjectContext = [[[NSManagedObjectContext alloc] init] autorelease]; [threadManagedObjectContext setPersistentStoreCoordinator: [self persistentStoreCoordinator]]; [[thisThread threadDictionary] setObject:threadManagedObjectContext forKey:CONTEXT_KEY]; } return threadManagedObjectContext; } } and when I pass object between threads i'm using -(NSManagedObject*)makeSafe:(NSManagedObject*)object { if ([object managedObjectContext] != [self managedObjectContext]) { NSError * error = nil; object = [[self managedObjectContext] existingObjectWithID:[object objectID] error:&error]; if (error) { NSLog(@"Error makeSafe: %@", error); } } return object; } Any help appreciated

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