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  • Help with Abstract Factory Pattern

    - by brazc0re
    I need help with a abstract factory pattern design. This question is a continuation of: Design help with parallel process I am really confused where I should be initializing all of the settings for each type of medium (ex: RS232, TCP/IP, etc). Attached is the drawing on how I am setting up the pattern: As shown, when a medium is created, each medium imposes a ICreateMedium interface. I would assume that the Create() method also create the proper object, such as SerialPort serialPort = new SerialPort("COM1", baud); however, TCPIPMedium would have an issue with the interface because it wouldn't need to initialize a serial port object. I know I am doing something majorly wrong here. I just can't figure it out and have been stuck for a while. What I also get confused on show the interface IMedium will get access to the communication object once it is created so it can write out the appropriate byte[] packet. Any guidance would be greatly appreciated. My main goal is to have the Communicator class spit a packet out without caring which type of medium is active.

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  • Php: Overriding abstract method goes wrong

    - by Lu4
    Hi! I think there is a problem in php's OOP implementation. EDIT: Consider more illustrative example: abstract class Animal { public $name; // public function Communicate(Animal $partner) {} // Works public abstract function Communicate(Animal $partner); // Gives error } class Panda extends Animal { public function Communicate(Panda $partner) { echo "Hi {$partner->name} I'm a Panda"; } } class Human extends Animal { public function Communicate(Human $partner) { echo "Hi {$partner->name} I'm a Human"; } } $john = new Human(); $john->name = 'John'; $mary = new Human(); $mary->name = 'Mary'; $john->Communicate($mary); // should be ok $zuzi = new Panda(); $zuzi->name = 'Zuzi'; $zuzi->Communicate($john); // should give error The problem is that when Animal::Communicate is an abstract method, php tells that the following methods are illegal: "public function Communicate(Panda $partner)" "public function Communicate(Human $partner)" but when Animal::Communicate is non-abstract but has zero-implementation Php thinks that these methods are legal. So in my opinion it's not right because we are doing override in both cases, and these both cases are equal, so it seems like it's a bug... Older part of the post: Please consider the following code: Framework.php namespace A { class Component { ... } abstract class Decorator { public abstract function Decorate(\A\Component $component); } } Implementation.php namespace B { class MyComponent extends \A\Component { ... } } MyDecorator.php namespace A { class MyDecorator extends Decorator { public function Decorate(\B\MyComponent $component) { ... } } } The following code gives error in MyDecorator.php telling Fatal error: Declaration of MyDecorator::Decorate() must be compatible with that of A\Decorator::Decorate() in MyDecorator.php on line ... But when I change the Framework.php::Decorator class to the following implementation: abstract class Decorator { public function Decorate(\A\Component $component) {} } the problem disappears.

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  • Rewrite probabilities as boolean algebra

    - by Magsol
    I'm given three binary random variables: X, Y, and Z. I'm also given the following: P(Z | X) P(Z | Y) P(X) P(Y) I'm then supposed to determine whether or not it is possible to find P(Z | Y, X). I've tried rewriting the solution in the form of Bayes' Theorem and have gotten nowhere. Given that these are boolean random variables, is it possible to rewrite the system in terms of boolean algebra? I understand that the conditionals can be mapped to boolean implications (x -> y, or !x + y), but I'm unsure how this would translate in terms of the overall problem I'm trying to solve. (yes, this is a homework problem, but here I'm much more interested in how to formally solve this problem than what the solution is...I also figured this question would be entirely too simple for MathOverflow)

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  • How to add member variable to an interface in c#

    - by Nassign
    I know this may be basic but I cannot seem to add a member variable to an interface. I tried inheriting the interface to an abstract class and add member variable to the abstract class but it still does not work. Here is my code: public interface IBase { void AddData(); void DeleteData(); } public abstract class AbstractBase : IBase { string ErrorMessage; abstract AddData(); abstract DeleteData(); }

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  • Why can't create object of an abstract class?

    - by Gaurav
    Here is a scenario in my mind and I have googled, Binged it a lot but got the answer like "Abstract class has not implemented method so, we cant create the object" "The word 'Abstract' instruct the clr that not to create object of the class" But in a simple class where we have all virtual method, able to create an object??? Also, we can define different access modified to Abstract class constructor like private, protected or public. My search terminated to this question ; Why we can't create object of an Abstract class?

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  • What is the difference between an Abstract Syntax Tree and a Concrete Syntax Tree?

    - by Jason Baker
    I've been reading a bit about how interpreters/compilers work, and one area where I'm getting confused is the difference between an AST and a CST. My understanding is that the parser makes a CST, hands it to the semantic analyzer which turns it into an AST. However, my understanding is that the semantic analyzer simply ensures that rules are followed. I don't really understand why it would actually make any changes to make it abstract rather than concrete. Is there something that I'm missing about the semantic analyzer, or is the difference between an AST and CST somewhat artificial?

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  • Should I be using abstract methods in this Python scenario?

    - by sfjedi
    I'm not sure my approach is good design and I'm hoping I can get a tip. I'm thinking somewhere along the lines of an abstract method, but in this case I want the method to be optional. This is how I'm doing it now... from pymel.core import * class A(object): def __init__(self, *args, **kwargs): if callable(self.createDrivers): self._drivers = self.createDrivers(*args, **kwargs) select(self._drivers) class B(A): def createDrivers(self, *args, **kwargs): c1 = circle(sweep=270)[0] c2 = circle(sweep=180)[0] return c1, c2 b = B() In the above example, I'm just creating 2 circle arcs in PyMEL for Maya, but I fully intend on creating more subclasses that may or may not have a createDrivers method at all! So I want it to be optional and I'm wondering if my approach is—well, if my approach could be improved?

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  • Java: reusable encapsulation with interface, abstract class or inner classes?

    - by HH
    I try to encapsulate. Exeption from interface, static inner class working, non-static inner class not working, cannot understand terminology: nested classes, inner classes, nested interfaces, interface-abstract-class -- sounds too Repetitive! Exception 'illegal type' from interface apparently because values being constants(?!) static interface userInfo { File startingFile=new File("."); String startingPath="dummy"; try{ startingPath=startingFile.getCanonicalPath(); }catch(Exception e){e.printStackTrace();} } Working code but no succes with non-static inner class import java.io.*; import java.util.*; public class listTest{ public interface hello{String word="hello word from Interface!";} public static class hej{ hej(){} private String hejo="hello hallo from Static class with image"; public void printHallooo(){System.out.println(hejo);} } public class nonStatic{ nonStatic(){} //HOW TO USE IT? public void printNonStatic(){System.out.println("Inside static class with an image!");} } public static void main(String[] args){ //INTERFACE TEST System.out.println(hello.word); //INNNER CLASS STATIC TEST hej h=new hej(); h.printHallooo(); //INNER CLASS NON-STATIC TEST nonStatic ns=new nonStatic(); ns.printNonStatic(); //IS there a way to it without STATIC? } } Output The above code works but how non-staticly? Output: hello word from Interface! hello hallo from Static class with image! StaticPrint without an image of the class! Related Nesting classes inner classes? interfacses

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  • How do I access abstract private data from derived class without friend or 'getter' functions in C++?

    - by John
    So, I am caught up in a dilemma right now. How am I suppose to access a pure abstract base class private member variable from a derived class? I have heard from a friend that it is possible to access it through the base constructor, but he didn't explain. How is it possible? There are some inherited classes from base class. Is there any way to gain access to the private variables ? class Base_button { private: bool is_vis; Rect rButton; public: // Constructors Base_button(); Base_button( const Point &corner, double height, double width ); // Destructor virtual ~ Base_button(); // Accessors virtual void draw() const = 0; bool clicked( const Point &click ) const; bool is_visible() const; // Mutators virtual void show(); virtual void hide(); void move( const Point &loc ); }; class Button : public Base_button { private: Message mButton; public: // Constructors Button(); Button( const Point &corner, const string &label ); // Acessors virtual void draw() const; // Mutators virtual void show(); virtual void hide(); }; I want to be able access Rect and bool in the base class from the subclass

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  • Implement two functions with the same name but different, non-covariant return types due to multiple abstract base classes

    - by user1508167
    If I have two abstract classes defining a pure virtual function with the same name, but different, non-covariant return types, how can I derive from these and define an implementation for both their functions? #include <iostream> class ITestA { public: virtual ~ITestA() {}; virtual float test() =0; }; class ITestB { public: virtual ~ITestB() {}; virtual bool test() =0; }; class C : public ITestA, public ITestB { public: /* Somehow implement ITestA::test and ITestB::test */ }; int main() { ITestA *a = new C(); std::cout << a->test() << std::endl; // should print a float, like "3.14" ITestB *b = dynamic_cast<ITestB *>(a); if (b) { std::cout << b->test() << std::endl; // should print "1" or "0" } delete(a); return 0; } As long as I don't call C::test() directly there's nothing ambiguous, so I think that it should work somehow and I guess I just didn't find the right notation yet. Or is this impossible, if so: Why?

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  • F#: Define an abstract class that inherits an infterface, but does not implement it

    - by akaphenom
    I owuld like to define an abstract class that inerhits from UserControl and my own Interface IUriProvider, but doesn't implement it. The goal is to be able to define pages (for silverlight) that implement UserControl but also provide their own Uri's (and then stick them in a list / array and deal with them as a set: type IUriProvider = interface abstract member uriString: String ; abstract member Uri : unit -> System.Uri ; end type UriUserControl() as this = inherit IUriProvider with abstract member uriString: String ; inherit UserControl() Also the Uri in the definition - I would like to implement as a property getter - and am having issues with that as well. this does not compile type IUriProvider = interface abstract member uriString: String with get; end Thank you...

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  • Java - binary compatibility of abstract class & subclasses

    - by thSoft
    In Java, I define an abstract class with both concrete and abstract methods in it, and it has to be subclassed independently by third-party developers. Just to be sure: are there any changes I could make to the abstract class that are source compatible with their classes but not binary compatible? In other words: after they have compiled their subclasses, could I change the abstract class - apart from e.g. adding an abstract method to it or removing a protected method from it that is called by subclasses, which are of course source incompatible - in a way that could force them to recompile their subclasses?

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  • Is it possible to use XStream with an abstract node?

    - by Dan Watling
    My client application is making calls to a service that returns a common "root" XML, but a different result node. The "root" XML contains possible error codes. Is it possible to use XStream in this scenario? Example: public class RootNode { ErrorInfo errorInfo; BaseResult result; ... } public class ErrorInfo { String message; ... } public abstract BaseResult { } public class SearchResult extends BaseResult { List<Object> searchResults; ... } public class AccountResult extends BaseResult { String name; ... } The XML coming back could be one of two formats: <root> <errorInfo><message>...</message></errorInfo> <result> <searchResults>...</searchResults> </result> </root> OR <root> <errorInfo><message>...</message></errorInfo> <result> <name>...</name> </result> </root> I have set up my XStream object as follows: XStream x = new XStream(); x.alias("root", Root.class); x.alias("errorInfo", ErrorInfo.class); x.alias("result", <SearchResult.class OR AccountResult.class depending on what I am expecting back>); Of course, when I run this I receive an error telling me XStream cannot instantiate the base class (BaseResult). For fun, I also converted the BaseResult into an interface but received a similar error. I've looked through XStream's documentation and it isn't clear to me how to handle a situation like the one I just described. Is it even possible to do using XStream? Thanks, -Dan

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  • How to write a cctor and op= for a factory class with ptr to abstract member field?

    - by Kache4
    I'm extracting files from zip and rar archives into raw buffers. I created the following to wrap minizip and unrarlib: Archive.hpp #include "ArchiveBase.hpp" #include "ArchiveDerived.hpp" class Archive { public: Archive(string path) { /* logic here to determine type */ switch(type) { case RAR: archive_ = new ArchiveRar(path); break; case ZIP: archive_ = new ArchiveZip(path); break; case UNKNOWN_ARCHIVE: throw; break; } } Archive(Archive& other) { archive_ = // how do I copy an abstract class? } ~Archive() { delete archive_; } void passThrough(ArchiveBase::Data& data) { archive_->passThrough(data); } Archive& operator = (Archive& other) { if (this == &other) return *this; ArchiveBase* newArchive = // can't instantiate.... delete archive_; archive_ = newArchive; return *this; } private: ArchiveBase* archive_; } ArchiveBase.hpp class ArchiveBase { public: // Is there any way to put this struct in Archive instead, // so that outside classes instantiating one could use // Archive::Data instead of ArchiveBase::Data? struct Data { int field; }; virtual void passThrough(Data& data) = 0; /* more methods */ } ArchiveDerived.hpp "Derived" being "Zip" or "Rar" #include "ArchiveBase.hpp" class ArchiveDerived : public ArchiveBase { public: ArchiveDerived(string path); void passThrough(ArchiveBase::Data& data); private: /* fields needed by minizip/unrarlib */ // example zip: unzFile zipFile_; // example rar: RARHANDLE rarFile_; } ArchiveDerived.cpp #include "ArchiveDerived.hpp" ArchiveDerived::ArchiveDerived(string path) { //implement } ArchiveDerived::passThrough(ArchiveBase::Data& data) { //implement } Somebody had suggested I use this design so that I could do: Archive archiveFile(pathToZipOrRar); archiveFile.passThrough(extractParams); // yay polymorphism! How do I write a cctor for Archive? What about op= for Archive? What can I do about "renaming" ArchiveBase::Data to Archive::Data? (Both minizip and unrarlib use such structs for input and output. Data is generic for Zip & Rar and later is used to create the respective library's struct.)

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  • How are the conceptual pairs Abstract/Concrete, Generic/Specific, and Complex/Simple related to one another in software architecture?

    - by tjb1982
    (= 2 (+ 1 1)) take the above. The requirement of the '=' predicate is that its arguments be comparable. Any two structures are comparable in this case, and so the contract/requirement is pretty generic. The '+' predicate requires that its arguments be numbers. That's more specific. (socket domain type protocol) the arguments here are much more specific (even though the arguments are still just numbers and the function itself returns a file descriptor, which is itself an int), but the arguments are more abstract, and the implementation is built up from other functions whose abstractions are less abstract, which are themselves built from less and less abstract abstractions. To the point where the requirements are something like move from one location to another, observe whether the switch at that location is on or off, turn the switch on or off, or leave it the same, etc. But are functions also less and less complex the less abstract they are? And is there a relationship between the number and range of arguments of a function and the complexity of its implementation, as you go from more abstract to less abstract, and vice versa? (= 2 (+ 1 1) 2r10) the '=' predicate is more generic than the '+' predicate, and thus could be more complex in its implementation. The '+' predicate's contract is less generic, and so could be less complex in its implementation. Is this even a little correct? What about the 'socket' function? Each of those arguments is a number of some kind. What they represent, though, is something more elaborate. It also returns a number (just like the others do), which is also a representation of something conceptually much more elaborate than a number. To boil it down, I'm asking if there is a relationship between the following dimensions, and why: Abstract/Concrete Complex/Simple Generic/Specific And more specifically, do different configurations of these dimensions have a specific, measurable impact on the number and range of the arguments (i.e., the contract) of a function?

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  • How can I split abstract testcases in JUnit?

    - by Willi Schönborn
    I have an abstract testcase "AbstractATest" for an interface "A". It has several test methods (@Test) and one abstract method: protected abstract A unit(); which provides the unit under testing. No i have multiple implementations of "A", e.g. "DefaultA", "ConcurrentA", etc. My problem: The testcase is huge (~1500 loc) and it's growing. So i wanted to split it into multiple testcases. How can organize/structure this in Junit 4 without the need to have a concrete testcase for every implementation and abstract testcase. I want e.g. "AInitializeTest", "AExectueTest" and "AStopTest". Each being abstract and containing multiple tests. But for my concrete "ConcurrentA", i only want to have one concrete testcase "ConcurrentATest". I hope my "problem" is clear. EDIT Looks like my description was not that clear. Is it possible to pass a reference to a test? I know parameterized tests, but these require static methods, which is not applicable to my setup. Subclasses of an abstract testcase decide about the parameter.

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  • Abstract Design Pattern implementation

    - by Pathachiever11
    I started learning design patterns a while ago (only covered facade and abstract so far, but am enjoying it). I'm looking to apply the Abstract pattern to a problem I have. The problem is: Supporting various Database systems using one abstract class and a set of methods and properties, which then the underlying concrete classes (inheriting from abstract class) would be implementing. I have created a DatabaseWrapper abstract class and have create SqlClientData and MSAccessData concrete class that inherit from the DatabaseWrapper. However, I'm still a bit confused about how the pattern goes as far as implementing these classes on the Client. Would I do the following?: DatabaseWrapper sqlClient = new SqlClientData(connectionString); This is what I saw in an example, but that is not what I'm looking for because I want to encapsulate the concrete classes; I only want the Client to use the abstract class. This is so I can support for more database systems in the future with minimal changes to the Client, and creating a new concrete class for the implementations. I'm still learning, so there might be a lot of things wrong here. Please tell me how I can encapsulate all the concrete classes, and if there is anything wrong with my approach. Many Thanks! PS: I'm very excited to get into software architecture, but still am a beginner, so take it easy on me. :)

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  • Scala factory pattern returns unusable abstract type

    - by GGGforce
    Please let me know how to make the following bit of code work as intended. The problem is that the Scala compiler doesn't understand that my factory is returning a concrete class, so my object can't be used later. Can TypeTags or type parameters help? Or do I need to refactor the code some other way? I'm (obviously) new to Scala. trait Animal trait DomesticatedAnimal extends Animal trait Pet extends DomesticatedAnimal {var name: String = _} class Wolf extends Animal class Cow extends DomesticatedAnimal class Dog extends Pet object Animal { def apply(aType: String) = { aType match { case "wolf" => new Wolf case "cow" => new Cow case "dog" => new Dog } } } def name(a: Pet, name: String) { a.name = name println(a +"'s name is: " + a.name) } val d = Animal("dog") name(d, "fred") The last line of code fails because the compiler thinks d is an Animal, not a Dog.

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  • Liskov substitution and abstract classes / strategy pattern

    - by Kolyunya
    I'm trying to follow LSP in practical programming. And I wonder if different constructors of subclasses violate it. It would be great to hear an explanation instead of just yes/no. Thanks much! P.S. If the answer is no, how do I make different strategies with different input without violating LSP? class IStrategy { public: virtual void use() = 0; }; class FooStrategy : public IStrategy { public: FooStrategy(A a, B b) { c = /* some operations with a, b */ } virtual void use() { std::cout << c; } private: C c; }; class BarStrategy : public IStrategy { public: BarStrategy(D d, E e) { f = /* some operations with d, e */ } virtual void use() { std::cout << f; } private: F f; };

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  • How exactly is an Abstract Syntax Tree created?

    - by Howcan
    I think I understand the goal of an AST, and I've build a couple of tree structures before, but never an AST. I'm mostly confused because the nodes are text and not number, so I can't think of a nice way to input a token/string as I'm parsing some code. For example, when I looked at diagrams of AST's, the variable and its value were leaf nodes to an equal sign. This makes perfect sense to me, but how would I go about implementing this? I guess I can do it case by case, so that when I stumble upon an "=" I use that as a node, and add the value parsed before the "=" as the leaf. It just seems wrong, because I'd probably have to make cases for tons and tons of things, depending on the syntax. And then I came upon another problem, how is the tree traversed? Do I go all the way down the height, and go back up a node when I hit the bottom, and do the same for it's neighbor? I've seen tons of diagrams on ASTs, but I couldn't find a fairly simple example of one in code, which would probably help.

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