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

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

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  • benefit of having a factory for object creation?

    - by ajsie
    I'm trying to understand the factory design pattern. I don't understand why it's good to have a middleman between the client and the product (object that the client wants). example with no factory: $mac = new Mac(); example with a factory: $appleStore = new AppleStore(); $mac = $appleStore->getProduct('mac'); How does the factory pattern decouple the client from the product? Could someone give an example of a future code change that will impact on example 1 negative, but positive in example 2 so I understand the importance of decoupling? Thanks.

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  • Exception in Google App Engine (Java) while trying to create Memcache Object

    - by Shreeni
    I am coming back to an old Google App Engine project on which I saw a bug. During this lag, I have been upgrading my AppEngine SDK and is now set at 1.3. When I try to run the same project again, I see the following exception: java.lang.NoSuchMethodError: com.google.apphosting.api.ApiProxy$Environment.getDefaultNamespace()Ljava/lang/String; at com.google.appengine.api.NamespaceManager.get(NamespaceManager.java:56) at com.google.appengine.api.memcache.MemcacheServiceImpl.setNamespace(MemcacheServiceImpl.java:181) at com.google.appengine.api.memcache.MemcacheServiceImpl.(MemcacheServiceImpl.java:145) at com.google.appengine.api.memcache.MemcacheServiceFactory.getMemcacheService(MemcacheServiceFactory.java:25) The line causing the problem is: CacheManager.getInstance().getCacheFactory().createCache(Collections.emptyMap()); (It is the same line as suggested by the AppEngine documentation to create a memcache object. It used to work fine previously. ) Any suggestions on how to fix it?

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  • Sharing class member data between sub components

    - by Tim Gradwell
    I have an aggregate 'main' class which contains some data which I wish to share. The main class also has other class members. I want to share the data with these other class members. What is the correct / neatest way to do this? The specific example I have is as follows. The main class is a .net Form. I have some controls (actually controls within controls) on the main form which need access to the shared data. Main Form - DataX - DataY - Control1 -- Subcontrol1 - Control2 -- SubControl2 SubControls 1 and 2 both wish to access DataX and DataY. The trouble is, I feel like better practice (to reduce coupling), would be that either subcontrols should not know about Main Form, or Main Form should not know about subcontrols - probably the former. For subcontrols not to know about Main Form, would probably mean Main Form passing references to both Controls 1 and 2, which in turn would pass the references on to SubControls 1 and 2. Lots of lines of code which just forward the references. If I later added DataZ and DataW, and Controls 3 and 4 and SubControls 3 and 4, I'd have to add lots more reference forwarding code. It seems simpler to me to give SubControls 1 and 2 member references to Main Form. That way, any sub control could just ask for MainForm.DataX or MainForm.DataY and if I ever added new data, I could just access it directly from the sub controls with no hassle. But it still involves setting the 'MainForm' member references every time I add a new Control or Subcontrol. And it gives me a gut feeling of 'wrong'. As you might be able to tell I'm not happy with either of my solutions. Is there a better way? Thanks

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  • Separating code logic from the actual data structures. Best practices?

    - by Patrick
    I have an application that loads lots of data into memory (this is because it needs to perform some mathematical simulation on big data sets). This data comes from several database tables, that all refer to each other. The consistency rules on the data are rather complex, and looking up all the relevant data requires quite some hashes and other additional data structures on the data. Problem is that this data may also be changed interactively by the user in a dialog. When the user presses the OK button, I want to perform all the checks to see that he didn't introduce inconsistencies in the data. In practice all the data needs to be checked at once, so I cannot update my data set incrementally and perform the checks one by one. However, all the checking code work on the actual data set loaded in memory, and use the hashing and other data structures. This means I have to do the following: Take the user's changes from the dialog Apply them to the big data set Perform the checks on the big data set Undo all the changes if the checks fail I don't like this solution since other threads are also continuously using the data set, and I don't want to halt them while performing the checks. Also, the undo means that the old situation needs to be put aside, which is also not possible. An alternative is to separate the checking code from the data set (and let it work on explicitly given data, e.g. coming from the dialog) but this means that the checking code cannot use hashing and other additional data structures, because they only work on the big data set, making the checks much slower. What is a good practice to check user's changes on complex data before applying them to the 'application's' data set?

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  • In what package should a "Settings" class be placed?

    - by Tom
    I'm in the middle of building an application but found myself too easily creating new packages without keeping the project's structure in mind. Now, I'm trying to redo the whole project structure on paper first. I am using a Settings class with public properties, accessed as settings for several other classes around the project. Now, since this Settings class applies for the whole project, I am unsure if it should be packaged and if so, in what kind of package should it exist? Or should it be in the root (the default package) with the main application class? I've been thinking about putting it in my utils package, then again I don't think it really is an utlity. Any strategies on how to decide on such package structure for example for a Settings class?

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  • Class with proprties that haven't been set

    - by koumides
    Hello there, I am creating a class in C# which eventually will be part of a library that other uses can use. A user of this class has to set some properties and then use a public method to retrieve the results. What shall I do when a user calls the method without setting all the properties? Throw exception and expect the user to catch it? Thanks

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  • Write a tree class in Java where each level has a unique object type

    - by user479576
    I need to write a tree class in Java where each level has a unique object type. The way it is written below does not take advantage of generics and causes alot of duplicate code. Is there a way to write this with Generics ? public class NodeB { private String nodeValue; //private List<NodeB> childNodes; // constructors // getters/setters } public class NodeA { private String value; private List<NodeB> childNodes; // constructors // getters/setters } public class Tree { private String value; private List<NodeA> childNodes; // constructors // tree methods }

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  • Singletons and constants

    - by devoured elysium
    I am making a program which makes use of a couple of constants. At first, each time I needed to use a constant, I'd define it as //C# private static readonly int MyConstant = xxx; //Java private static final int MyConstant = xxx; in the class where I'd need it. After some time, I started to realise that some constants would be needed in more than one class. At this time, I had 3 choises: To define them in the different classes that needed it. This leads to repetition. If by some reason later I need to change one of them, I'd have to check in all classes to replace them everywhere. To define a static class/singleton with all the constants as public. If I needed a constant X in ClassA, ClassB and ClassC, I could just define it in ClassA as public, and then have ClassB and ClassC refer to them. This solution doesn't seem that good to me as it introduces even more dependencies as the classes already have between them. I ended up implementing my code with the second option. Is that the best alternative? I feel I am probably missing some other better alternative. What worries me about using the singleton here is that it is nowhere clear to a user of the class that this class is using the singleton. Maybe I could create a ConstantsClass that held all the constants needed and then I'd pass it in the constructor to the classes that'd need it? Thanks

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  • Trying to re-create UI object from the native iPhone Calendar Notes

    - by FrankOS
    Probably a lame question for a start but i'm trying to re-create the ui object that's used in Apple's native Calendar to create notes. It's the basic text-field but with multiple lines. Sort of a text-area. Now i know that anything from the calendar in terms of ui objects isn't available but i have seen this in quite few apps so i'm guessing it's some sort of standard component. I must be dumb but i just cannot find it. Help please... Thx :)

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  • How can I call a Perl package I define in the same file?

    - by Robert S. Barnes
    I need to define some modules and use them all in the same file. No, I can't change the requirement. I would like to do something like the following: { package FooObj; sub new { ... } sub add_data { ... } } { package BarObj; use FooObj; sub new { ... # BarObj "has a" FooObj my $self = ( myFoo => FooObj->new() ); ... } sub some_method { ... } } my $bar = BarObj->new(); However, this results in the message: Can't locate FooObj.pm in @INC ... BEGIN failed... How do I get this to work?

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  • Ruby on Rails - can't access datetime model object

    - by NomadicRiley
    I've created a model that has 3 string columns and a datetime. Everything is running in SQLite3 and I can view the records in my table just fine using Lita. I'm trying to display the values in a page (index action) using code like this: <% @details.each do |lifeCycle| % <%= debug(lifeCycle)% <%= lifeCycle.lifeCycleId % <%= lifeCycle.eventType % <%= debug(lifeCycle.timeId) % <% end % From the debug I get a result like this: --- !ruby/object:LifeCycle attributes: eventType: Order created_at: "2111359287.23037" timeId: "2455364.89983796" eventId: "98765" updated_at: "2111359287.23037" lifeCycleId: "12345" id: "1" attributes_cache: {} But whenever I try to access the event timeId - i' getting a nil value. This is true if i try to run debug on just that field debug(lifeCycle.timeId), or call a function on it. Is there something obvious I'm missing here?

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  • Does this pattern have a name?

    - by LK7jb
    Disclaimer: I'm trying to learn proper OO programming/design, so I'm pretty new to this stuff. I guess this is a general design patterns question, but I'll base my example on a game engine or something that renders objects to the display. Consider the following: How can this sort of separation between physical objects (e.g., cubes, spheres, etc.) and the rendering mechanism be achieved in an extensible manner? This design is not set in stone, and perhaps I've got something wrong from the start. I'm just curious as to how a problem like this is solved in real world code.

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  • Using a string as an object reference

    - by user317362
    I currently have a Javascript function that uses a string to reference an object name and acces its properties. I'm currently using eval() to get the the desired effect which I know is very, very wrong. Here is an example of how I'm currently achieving what I want: var stringToObjectRef = function() { var myTestVar = "myTestObject"; var myTestObject = { 'item1' : 100, 'item2' : 12, 'item4' : 18 }; var myValue = eval(myTestVar + '.item1'); alert(myValue); }(); I've tried using something like [myTestVar].item1, but this returns undefined. What is the correct syntax to achieve this? Thanks in advance.

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  • Creating non-framework calsses in CakePHP

    - by Affian
    I'm making a tournament manager in CakePHP 1.3 and I have a tournament controller which is fine but I want to implement a interface that can be used to define how a tournament runs. the controller needs to load a concrete class that implements the TournamentStyle interface that defines how the tournament works. At the end of a round the TournamentStyle is used to calculate the scores and winners and generate the next round of matches. That gives me a .php file for the interface and other files for the various styles. My question is: where would I put these files and how would I load them into my tournament controller?

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  • onclick from an Object's button doesn't work

    - by 730
    I instantiate an object, with an argument which is a button. When the button of an instance is clicked, it should run a function, but it doesn't. In the full version of the code, Chrome gives this message in the console: "Uncaught TypeError: Cannot read property 'onclick' of undefined" HTML: <textarea id='txt' readonly rows='5' cols='40'></textarea> <button id='btn' type='button'>click</button> JS: var btn = document.getElementById('btn'); var txt = document.getElementById('txt'); var foo = new Foo(btn); function Foo(btn) { this.button = btn; } Foo.prototype.buy = function() { txt.value = 'Foo Bar'; }; Foo.button.onclick = function() { foo.buy(); }; Fiddle

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  • Looking for a jquery plugin to serialize a form to an object

    - by John
    I'm looking for a jQuery function or plugin that serializes form inputs to an object using the naming convention for deep-serialization supported by param() in jQuery 1.4: <form> <input name="a[b]" value="1"/> <input name="a[c]" value="2"/> <input name="d[]" value="3"/> <input name="d[]" value="4"/> <input name="d[2][e]" value="5"/> </form> $('form').serializeObject(); // { a: { b:1,c:2 }, d: [3,4,{ e:5 }] } Prototype's Form.serialize method can do exactly this. What's the jQuery equivalent? I found this plugin but it doesn't follow this naming convention.

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  • Enums and inheritance

    - by devoured elysium
    I will use (again) the following class hierarchy: Event and all the following classes inherit from Event: SportEventType1 SportEventType2 SportEventType3 SportEventType4 I have originally designed the Event class like this: public abstract class Event { public abstract EventType EventType { get; } public DateTime Time { get; protected set; } protected Event(DateTime time) { Time = time; } } with EventType being defined as: public enum EventType { Sport1, Sport2, Sport3, Sport4 } The original idea would be that each SportEventTypeX class would set its correct EventType. Now that I think of it, I think this approach is totally incorrect for two reasons: If I want to later add a new SportEventType class I will have to modify the enum If I later decide to remove one SportEventType that I feel I won't use I'm also in big trouble with the enum. I have a class variable in the Event class that makes, afterall, assumptions about the kind of classes that will inherit from it, which kinda defeats the purpose of inheritance. How would you solve this kind of situation? Define in the Event class an abstract "Description" property, having each child class implement it? Having an Attribute(Annotation in Java!) set its Description variable instead? What would be the pros/cons of having a class variable instead of attribute/annotation in this case? Is there any other more elegant solution out there? Thanks

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  • syntax problem crating a method that returns an object (java)

    - by David
    I'm trying to create a method that will sum two timeO objects and return a new TimeO object called sum. Here is the relevant code snippet: public static TimeO add (TimeO t1, TimeO t2) { TimeO sum = new TimeO ; ... } When i try to compile it i get this error message: TimeO.java:15: '(' or '[' expected TimeO sum = new TimeO ; ^ 1 error i cant think of any reason why it would want me to open a set of parenthasies or brackets here but its possible that i dont' quite understand the syntax. Whats going wrong here?

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  • Adding interfaces that won't be actually used

    - by devoured elysium
    I currently have two interfaces(that I'll name here IA and IB): interface IA { int Width; int Height; ... } interface IB { int Width; int Height; ... } that share the same two properties: they both have a Width and a Height property. I was thinking if there is any point in defining an IMatrix interface containing a Width and Height properties: interface IMatrix { int Width; int Height; } The thing is that although they share both the same properties, I won't make use of polymorphism with IMatrix in any of my coding: i.e., there won't by any situation where I'll want to use an IMatrix, I'll just want to use IA and IB. Adding an IMatrix seems more like over-engineering than other thing, but I'd like to ask you guys what your opinion is on the matter. Thanks

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