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  • How to extend this design for a generic converter in java?

    - by Jay
    Here is a small currency converter piece of code: public enum CurrencyType { DOLLAR(1), POUND(1.2), RUPEE(.25); private CurrencyType(double factor) { this.factor = factor; } private double factor; public double getFactor() { return factor; } } public class Currency { public Currency(double value, CurrencyType type) { this.value = value; this.type = type; } private CurrencyType type; private double value; public CurrencyType getCurrencyType() { return type; } public double getCurrencyValue() { return value; } public void setCurrenctyValue(double value){ this.value = value; } } public class CurrencyConversion { public static Currency convert(Currency c1, Currency c2) throws Exception { if (c1 != null && c2 != null) { c2.setCurrenctyValue(c1.getCurrencyValue() * c1.getCurrencyType().getFactor() * c2.getCurrencyType().getFactor()); return c2; } else throw new Exception(); } } I would like to improve this code to make it work for different units of conversion, for example: kgs to pounds, miles to kms, etc etc. Something that looks like this: public class ConversionManager<T extends Convertible> { public T convert(T c1, T c2) { //return null; } } Appreciate your ideas and suggestions.

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  • Differentiate generic methods by type parameters only using reflection?

    - by Brian Vallelunga
    I'm trying to use reflection to get a specific MethodInfo of a class, but am unsure how to differentiate between the two following methods: public class Test { public IBar<T1> Foo<T1>(); public IBar<T1, T2> Foo<T1, T2>(); } How can I get a reference to the different Foo methods, assuming I know the number of type parameters? Just calling typeof(Test).GetMethod("Foo") will throw an exception that the method name is ambiguous and there aren't a differing number of parameters to check.

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  • How can I create a generic constructor? (ie. BaseClass.FromXml(<param>)

    - by SofaKng
    I'm not sure how to describe this but I'm trying to create a base class that contains a shared (factory) function called FromXml. I want this function to instantiate an object of the proper type and then fill it via an XmlDocument. For example, let's say I have something like this: Public Class XmlObject Public Shared Function FromXml(ByVal source as XmlDocument) As XmlObject // <need code to create SPECIFIC TYPE of object and return it End Function End Class Public Class CustomObject Inherits XmlObject End Class I'd like to be able to do something like this: Dim myObject As CustomObject = CustomObject.FromXml(source) Is this possible?

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  • How to solve generic algebra using solver/library programmatically? Matlab, Mathematica, Wolfram etc?

    - by DevDevDev
    I'm trying to build an algebra trainer for students. I want to construct a representative problem, define constraints and relationships on the parameters, and then generate a bunch of Latex formatted problems from the representation. As an example: A specific question might be: If y < 0 and (x+3)(y-5) = 0, what is x? Answer (x = -3) I would like to encode this as a Latex formatted problem like. If $y<0$ and $(x+constant_1)(y+constant_2)=0$ what is the value of x? Answer = -constant_1 And plug into my problem solver constant_1 > 0, constant_1 < 60, constant_1 = INTEGER constant_2 < 0, constant_2 > -60, constant_2 = INTEGER Then it will randomly construct me pairs of (constant_1, constant_2) that I can feed into my Latex generator. Obviously this is an extremely simple example with no real "solving" but hopefully it gets the point across. Things I'm looking for ideally in priority order * Solve algebra problems * Definition of relationships relatively straight forward * Rich support for latex formatting (not just writing encoded strings) Thanks!

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  • How do I put all types implementing a certain generic interface in a dictionary?

    - by James Wenday
    Given a particular interface ITarget<T> and a particular type myType, here's how you would determine T if myType implements ITarget<T>. (This code snippet is taken from the answer to an earlier question.) foreach (var i in myType.GetInterfaces ()) if (i.IsGenericType && i.GetGenericTypeDefinition() == typeof(ITarget<>)) return i.GetGenericArguments ()[0] ; However, this only checks a single type, myType. How would I create a dictionary of all such type parameters, where the key is T and the value is myType? I think it would look something like this: var searchTarget = typeof(ITarget<>); var dict = Assembly.GetExecutingAssembly().[???] .Where(t => t.IsGenericType && t.GetGenericTypeDefinition() == searchTarget) .[???]; What goes in the blanks?

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  • Can someone explain the declaration of these java generic methods?

    - by Tony Giaccone
    I'm reading "Generics in the Java Programming Language" by Gilad Bracha and I'm confused about a style of declaration. The following code is found on page 8: interface Collection<E> { public boolean containsAll(Collection<?> c); public boolean addAll(Collection<? extends E> c); } interface Collection<E> { public <T> boolean containsAll(Collection<T> c); public <T extends E> boolean addAll(Collection<T> c); // hey, type variables can have bounds too! } My point of confusion comes from the second declaration. It's not clear to me what the purpose the <T> declaration serves in the following line: public <T> boolean containsAll(Collection<T> c); The method already has a type (boolean) associated with it. Why would you use the <T> and what does it tell the complier? I think my question needs to be a bit more specific. Why would you write: public <T> boolean containsAll(Collection<T> c); vs public boolean containsAll(Collection<T> c); It's not clear to me, what the purpose of <T> is, in the first declaration of containsAll.

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  • How to call implemented method of generic enum in Java?

    - by Justin Wiseman
    I am trying pass an enum into a method, iterate over that enums values, and call the method that that enum implements on all of those values. I am getting compiler errors on the part "value.getAlias()". It says "The method getAlias() is undefined for the type E" I have attempted to indicate that E implements the HasAlias interface, but it does not seem to work. Is this possible, and if so, how do I fix the code below to do what I want? The code below is only meant to show my process, it is not my intention to just print the names of the values in an enum, but to demonstate my problem. public interface HasAlias{ String getAlias(); }; public enum Letters implements HasAlias { A("The letter A"), B("The letter B"); private final String alias; public String getAlias(){return alias;} public Letters(String alias) { this.alias = alias; } } public enum Numbers implements HasAlias { ONE("The number one"), TWO("The number two"); private final String alias; public String getAlias(){return alias;} public Letters(String alias) { this.alias = alias; } } public class Identifier { public <E extends Enum<? extends HasAlias>> void identify(Class<E> enumClass) { for(E value : enumClass.getEnumConstants()) { System.out.println(value.getAlias()); } } }

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  • How come Java doesn't accept my LinkedList in a Generic, but accepts its own?

    - by master chief
    For a class assignment, we can't use any of the languages bultin types, so I'm stuck with my own list. Anyway, here's the situation: public class CrazyStructure <T extends Comparable<? super T>> { MyLinkedList<MyTree<T>> trees; //error: type parameter MyTree is not within its bound } However: public class CrazyStructure <T extends Comparable<? super T>> { LinkedList<MyTree<T>> trees; } Works. MyTree impleements the Comparable interface, but MyLinkedList doesn't. However, Java's LinkedList doesn't implement it either, according to this. So what's the problem and how do I fix it? MyLinkedList: public class MyLinkedList<T extends Comparable<? super T>> { private class Node<T> { private Node<T> next; private T data; protected Node(); protected Node(final T value); } Node<T> firstNode; public MyLinkedList(); public MyLinkedList(T value); //calls node1.value.compareTo(node2.value) private int compareElements(final Node<T> node1, final Node<T> node2); public void insert(T value); public void remove(T value); } MyTree: public class LeftistTree<T extends Comparable<? super T>> implements Comparable { private class Node<T> { private Node<T> left, right; private T data; private int dist; protected Node(); protected Node(final T value); } private Node<T> root; public LeftistTree(); public LeftistTree(final T value); public Node getRoot(); //calls node1.value.compareTo(node2.value) private int compareElements(final Node node1, final Node node2); private Node<T> merge(Node node1, Node node2); public void insert(final T value); public T extractMin(); public int compareTo(final Object param); }

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  • Get the string "System.Collections.ObjectModel.ObservableCollection" from a Type (System.type) containing a generic ObservableCollection?

    - by Guillaume Cogranne
    I got a Type whose FullName is (if this helps) : "System.Collections.ObjectModel.ObservableCollection`1[[System.String, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]" From that Type, I'd like to get "System.Collections.ObjectModel.ObservableCollection" as a string but I'd like to do it "cleanly", which means, without spliting the string with the char '`'. I think the strategy is to get something like a Type or something else whose FullName will be "System.Collections.ObjectModel.ObservableCollection" but I really don't manage to do it :/

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  • Why doesn't Java allow for the creaton of generic arrays?

    - by byte
    There are plenty of questions on stackoverflow from people who have attempted to create an array of generics like so: ArrayList<Foo>[] poo = new ArrayList<Foo>[5]; And the answer of course is that the Java specification doesn't allow you to declare an array of generics. My question however is why ? What is the technical reason underlying this restriction in the java language or java vm? It's a technical curiosity I've always wondered about.

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  • How to call a generic method with an anonymous type involving generics?

    - by Alex Black
    I've got this code that works: def testTypeSpecialization = { class Foo[T] def add[T](obj: Foo[T]): Foo[T] = obj def addInt[X <% Foo[Int]](obj: X): X = { add(obj) obj } val foo = addInt(new Foo[Int] { def someMethod: String = "Hello world" }) assert(true) } But, I'd like to write it like this: def testTypeSpecialization = { class Foo[T] def add[X, T <% Foo[X](obj: T): T = obj val foo = add(new Foo[Int] { def someMethod: String = "Hello world" }) assert(true) } This second one fails to compile: no implicit argument matching parameter type (Foo[Int]{ ... }) = Foo[Nothing] was found. Basically: I'd like to create a new anonymous class/instance on the fly (e.g. new Foo[Int] { ... } ), and pass it into an "add" method which will add it to a list, and then return it The key thing here is that the variable from "val foo = " I'd like its type to be the anonymous class, not Foo[Int], since it adds methods (someMethod in this example) Any ideas? I think the 2nd one fails because the type Int is being erased. I can apparently 'hint' the compiler like this: def testTypeSpecialization = { class Foo[T] def add[X, T <% Foo[X]](dummy: X, obj: T): T = obj val foo = add(2, new Foo[Int] { def someMethod: String = "Hello world" }) assert(true) }

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  • Can i use a generic implicit or explicit operator? C#

    - by acidzombie24
    How do i change the following statement so it accepts any type instead of long? Now here is the catch, if there is no constructor i dont want it compiling. So if theres a constructor for string, long and double but no bool how do i have this one line work for all of these support types? ATM i just copied pasted it but i wouldnt like doing that if i had 20types (as trivial as the task may be) public static explicit operator MyClass(long v) { return new MyClass(v); }

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  • Open generic interface types of open implementation don't equal interface type?

    - by George Mauer
    Here's a test that should, in my opinion be passing but is not. [TestMethod] public void can_get_open_generic_interface_off_of_implementor() { typeof(OpenGenericWithOpenService<>).GetInterfaces().First() .ShouldEqual(typeof(IGenericService<>)); } public interface IGenericService<T> { } public class OpenGenericWithOpenService<T> : IGenericService<T> { } Why does this not pass? Given Type t = typeof(OpenGenericWithOpenService<>) how do I get typeof(IGenericService<)? I'm generally curious, but if you're wondering what I'm doing, I'm writing a Structuremap convention that forwards all interfaces implemented by a class to the implementation (as a singleton).

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  • How to keep a Generic list unmodified when its copy is modified?

    - by user1801934
    When I create a copy of the original list lstStudent in lstCopy and send the lstCopy to modification function, the lstStudent also gets modified. I want to keep this list unmodified. List<Student> lstStudent = new List<Student>(); Student s = new Student(); s.Name = "Akash"; s.ID = "1"; lstStudent.Add(s); List<Student> lstCopy = new List<Student>(lstStudent); Logic.ModifyList(lstCopy); // "Want to use lstStudent(original list) for rest part of the code" public static void ModifyList(List<Student> lstIntegers) { foreach (Student s in lstIntegers) { if (s.ID.Equals("1")) { s.ID = "4"; s.Name = "APS"; } } }

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  • Passing the Class<T> in java of a generic list?

    - by Rob Stevenson-Leggett
    I have a method for reading JSON from a service, I'm using Gson to do my serialization and have written the following method using type parameters. public T getDeserializedJSON(Class<T> aClass,String url) { Reader r = getJSONDataAsReader(url); Gson gson = new Gson(); return gson.fromJson(r, aClass); } I'm consuming json which returns just an array of a type e.g. [ { "prop":"value" } { "prop":"value" } ] I have a java class which maps to this object let's call it MyClass. However to use my method I need to do this: RestClient<ArrayList<MyClass>> restClient = new RestClient<ArrayList<MyClass>>(); ArrayList<MyClass> results = restClient.getDeserializedJSON(ArrayList<MyClass>.class, url); However, I can't figure out the syntax to do it. Passing just ArrayList.class doesn't work. So is there a way I can get rid of the Class parameter or how do I get the class of the ArrayList of MyClass?

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  • Could I return a FileStream as a generic interface to a file?

    - by Eric
    I'm writing a class interface that needs to return references to binary files. Typically I would provide a reference to a file as a file path. However, I'm considering storing some of the files (such as a small thumbnail) in a database directly rather then on a file system. In this case I don't want to add the extra step of reading the thumbnail out of the database onto the disc and then returning a path to the file for my program to read. I'd want to stream the image directly out of the database into my program and avoid writing anything to the disc unless the user explicit wants to save something. Would having my interface return a FileStreamor even a Imagemake sense? Then it would be up to the implementing class to determine if the source of the FileStream or Image is a file on a disc or binary data in a database. public interface MyInterface { string Thumbnail {get;} string Attachment {get;} } vs public interface MyInterface { Image Thumbnail {get;} FileStream Attachment {get;} }

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  • PropertyInfo.GetValue() - how do you index into a generic parameter using reflection in C#?

    - by flesh
    This (shortened) code.. for (int i = 0; i < count; i++) { object obj = propertyInfo.GetValue(Tcurrent, new object[] { i }); } .. is throwing a 'TargetParameterCountException : Parameter count mismatch' exception. The underlying type of 'propertyInfo' is a Collection of some T. 'count' is the number of items in the collection. I need to iterate through the collection and perform an operation on obj. Advice appreciated.

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  • Is possible to set generic type by another class?

    - by Soul_Master
    I use ASP.NET MVC for serving web application and I want to create something like the following code. <% using(HTML.Form(Model)) { %> <% HTML.CreateTextBox('txt1', x => x.Property1); <% } From the above code, Form extension method will receive object that represent type of current Model object in current View page. Next, CreateTextBox method will receive type from Form method and I can bind textbox to some property of this model. Update 1 The following code is code of CreateTextBox method that will create instance of TextBox class. public static CreateTextBox(string value, Expression<Func<object>> bindedProperty) { // T should be receive from HTML.Form method or class return new TextBox<T>(value); } Is it possible to creating some code that doing something like the above code? Thanks,

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