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• Specialization hierarchy in a domain-model

  - by devoured elysium

  I'm trying to make the domain model of a management system. I have the following kinds of persons in this system: employee manager top mananger I decided to define a User, from where employee, manager and top manager will specialize from. What I don't know is what kind of specialization hierarchy I should choose from. I thought of two ways: or Which might be preferable and why? As a long time coder, every time I try to do a domain-model, I have to fight against the idea of trying to think in how I'm going to code this. From what I've understood, I should not think about those matters in the domain-model, only in object relationships. I don't have to think of code duplication or any of these kind of details here, so I can't really pick any of the options over the other. Thanks

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• How to define a predicate as a function argument

  - by devoured elysium

  I want to be able to write something as void Start(some condition that might evaluate to either true or false) { //function will only really start if the predicate evaluates to true } I'd guess it must be something of the form: void Start(Predicate predicate) { } How can I check inside my Start function whenever the predicate evaluated to true or false? Is my use of a predicate correct? Thanks

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• Class hierarchy problem (with generic's variance!)

  - by devoured elysium

  The problem: class StatesChain : IState, IHasStateList { private TasksChain tasks = new TasksChain(); ... public IList<IState> States { get { return _taskChain.Tasks; } } IList<ITask> IHasTasksCollection.Tasks { get { return _taskChain.Tasks; } <-- ERROR! You can't do this in C#! I want to return an IList<ITask> from an IList<IStates>. } } Assuming the IList returned will be read-only, I know that what I'm trying to achieve is safe (or is it not?). Is there any way I can accomplish what I'm trying? I wouldn't want to try to implement myself the TasksChain algorithm (again!), as it would be error prone and would lead to code duplication. Maybe I could just define an abstract Chain and then implement both TasksChain and StatesChain from there? Or maybe implementing a Chain<T> class? How would you approach this situation? The Details: I have defined an ITask interface: public interface ITask { bool Run(); ITask FailureTask { get; } } and a IState interface that inherits from ITask: public interface IState : ITask { IState FailureState { get; } } I have also defined an IHasTasksList interface: interface IHasTasksList { List<Tasks> Tasks { get; } } and an IHasStatesList: interface IHasTasksList { List<Tasks> States { get; } } Now, I have defined a TasksChain, that is a class that has some code logic that will manipulate a chain of tasks (beware that TasksChain is itself a kind of ITask!): class TasksChain : ITask, IHasTasksList { IList<ITask> tasks = new List<ITask>(); ... public List<ITask> Tasks { get { return _tasks; } } ... } I am implementing a State the following way: public class State : IState { private readonly TaskChain _taskChain = new TaskChain(); public State(Precondition precondition, Execution execution) { _taskChain.Tasks.Add(precondition); _taskChain.Tasks.Add(execution); } public bool Run() { return _taskChain.Run(); } public IState FailureState { get { return (IState)_taskChain.Tasks[0].FailureTask; } } ITask ITask.FailureTask { get { return FailureState; } } } which, as you can see, makes use of explicit interface implementations to "hide" FailureTask and instead show FailureState property. The problem comes from the fact that I also want to define a StatesChain, that inherits both from IState and IHasStateList (and that also imples ITask and IHasTaskList, implemented as explicit interfaces) and I want it to also hide IHasTaskList's Tasks and only show IHasStateList's States. (What is contained in "The problem" section should really be after this, but I thought puting it first would be way more reader friendly). (pff..long text) Thanks!

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• Problem running code with JML2 in Eclipse

  - by devoured elysium

  I'm having trouble running JML2 in Eclipse. I have the foolowing code: public class MainClass { public static void main(String[] args) { System.out.println(-9.0); } //@requires x >= 7.0 public static double getSquare(double x) { return Math.sqrt(x); } } The error I'm getting is: Is there anything wrong with the syntax I've used? Thanks

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• Continuous output in Neural Networks

  - by devoured elysium

  How can I set Neural Networks so they accept and output a continuous range of values instead of a discrete ones? From what I recall from doing a Neural Network class a couple of years ago, the activation function would be a sigmoid, which yields a value between 0 and 1. If I want my neural network to yield a real valued scalar, what should I do? I thought maybe if I wanted a value between 0 and 10 I could just multiply the value by 10? What if I have negative values? Is this what people usually do or is there any other way? What about the input? Thanks

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• What's the reason both Image and Bitmap classes don't implement a custom equality/hashcode logic?

  - by devoured elysium

  From MSDN documentation, it seems as both GetHashCode() and Equals() haven't been overriden in Bitmap. Neither have them been overriden in Image. So both classes are using the Object's version of them just compares references. I wasn't too convinced so I decided to fire up Reflector to check it out. It seems MSDN is correct in that matter. So, is there any special reason why MS guys wouldn't implement "comparison logic", at least for the Bitmap class? I find it is kinda acceptable for Image, as it is an abstract class, but not so much for the Bitmap class. I can see in a lot of situations calculating the hash code can be an expensive operation, but it'd be alright if it used some kind of lazy evaluation (storing the computed hash code integer in a variable a variable, so it wouldn't have to calculate it later again). When wanting to compare 2 bitmaps, will I have to resort to having to run all over the picture comparing each one of its pixels? Thanks

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• Awkward looking uses of Contract.ValueAtReturn()

  - by devoured elysium

  I am designing a method that will add an element to an internal list. The structure of the class is something along the lines of: class MyCustomerDatabase { private IList<Customer> _customers = new List<Customer>(); public int NumberOfCustomers { get { return _customers; } } public void AddCustomer(Customer customer) { _customers.Add(customer); } } Now, I was thinking of adding a Contract.Ensures() about the size of the _customers growing by 1 with this call. The problem is that I end up with some weird looking code: public void AddCustomer(Customer customer) { int numberOfCustomersAtReturn; Contract.Ensures(Contract.ValueAtReturn<int>(out numberOfCustomersAtReturn) == Contract.OldValue<int>(NumberOfCustomers) + 1); _customers.Add(customer); numberOfCustomersAtReturn = NumberOfCustomers; } The main problem is that properties are in fact methods, so you can't just reference them direcly when using Contract.ValueAtReturn() as its only parameter accepts variables as out. The situation gets even odder if I want to achieve the same but this time with a method that should return a value: public int MyReturningMethod() { ... return abc(); //abc will add by one the number of customers in list } //gets converted to public int MyReturningMethod() { int numberOfCustomersAtReturn; Contract.Ensures(Contract.ValueAtReturn<int>(out numberOfCustomersAtReturn) == Contract.OldValue<int>(NumberOfCustomers) + 1); int returnValue = abc(); numberOfCustomersAtReturn = NumberOfCustomers; return returnValue; } This seems pretty clumsy :( Code Contracts should aim to get things clearer and this seems right the opposite. Am I doing something wrong? Thanks

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• Getting Unit Tests to work with Komodo IDE for Python

  - by devoured elysium

  I've tried to run the following code on Komodo IDE (for python): import unittest class MathLibraryTests(unittest.TestCase): def test1Plus1Equals2(self): self.assertEqual(1+1, 2) Then, I created a new test plan, pointing to this project(file) directory and tried to run it the test plan. It seems to run but it doesn't seem to find any tests. If I try to run the following code with the "regular" run command (F7) class MathLibraryTests(unittest.TestCase): def testPlus1Equals2(self): self.assertEqual(1+1, 2) if __name__ == "__main__": unittest.main() it works. I get the following output: ---------------------------------------------------------------------- Ran 1 test in 0.000s OK What might I be doing wrong?

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• Using collections/containers/catalogs in Domain Models

  - by devoured elysium

  Let's say I want to model a cinema. The cinema will have a couple of rooms(for example, 7), where the movies are being played. I wonder how should I design the domain model for this scenario. Should the Cinema class concept concept have a direct association with the 7 rooms? Should the Cinema class concept have an association with a catalog of the 7 rooms? Why? I am having some trouble understanding why in some places I see the first case and in some others I see something like the second case. If instead of rooms, I wanted to depict the relationship between Cinema and: Tickets to sell (today). Tickets already sold (today) Customers in the Cinema database The set of hours at which there are movies playing in a given room in the cinema. The set of places you can sit at in a room in the cinema. Should I use catalogs, should I connect them directly to the Cinema concept with a multiplicity of * in the target? Thanks

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• When defining a class as internal, do you define what would usually be public fields as internal?

  - by devoured elysium

  When defining a class as internal, do you define what would usually be public fields as internal? Or do you leave them as public? I have a set of classes with public/private methods that I have decided to set as internal. Now, should I change the class' modifier to internal and let the rest of the methods/properties as they are (public/private) or switch them to (internal/private)? I don't see a big point in changing it to internal, and if by some reason later I want to set them back to public it's going to give a lot of work to have to put them back to public again. Any other thoughts on this?

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• Better to use constructor or method factory pattern?

  - by devoured elysium

  I have a wrapper class for the Bitmap .NET class called BitmapZone. Assuming we have a WIDTH x HEIGHT bitmap picture, this wrapper class should serve the purpose of allowing me to send to other methods/classes itself instead of the original bitmap. I can then better control what the user is or not allowed to do with the picture (and I don't have to copy the bitmap lots of times to send for each method/class). My question is: knowing that all BitmapZone's are created from a Bitmap, what do you find preferrable? Constructor syntax: something like BitmapZone bitmapZone = new BitmapZone(originalBitmap, x, y, width, height); Factory Method Pattern: BitmapZone bitmapZone = BitmapZone.From(originalBitmap, x , y, width, height); Factory Method Pattern: BitmapZone bitmapZone = BitmapZone.FromBitmap(originalBitmap, x, y, width, height); Other? Why? Thanks

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• Check if there are any repeated elements in a array recursively

  - by devoured elysium

  I have to find recursively if there is any repeated element in an integer array v. The method must have the following signature: boolean hasRepeatedElements(int[] v) I can't see any way of doing that recursively without having to define another method or at least another overload to this method (one that takes for example the element to go after or something). At first I thought about checking for the current v if there is some element equal to the first element, then creating a new array with L-1 elements etc but that seems rather inefficient. Is it the only way? Am I missing here something?

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• Problem with "scopes" of variables in try catch blocks in Java

  - by devoured elysium

  Could anyone explain me why in the last lines, br is not recognized as variable? I've even tried putting br in the try clause, setting it as final, etc. Does this have anything to do with Java not support closures? I am 99% confident similar code would work in C#. private void loadCommands(String fileName) { try { final BufferedReader br = new BufferedReader(new FileReader(fileName)); while (br.ready()) { actionList.add(CommandFactory.GetCommandFromText(this, br.readLine())); } } catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } finally { if (br != null) br.close(); //<-- This gives error. It doesn't // know the br variable. } } Thanks

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• Question about [Pure] methods

  - by devoured elysium

  Is the following method Pure? I'd say so, as it doesn't change in anyway the current class, thus, everything we can now currenly "see" in the class, before running this method will still be exactly the same after. Am I correct? class Set { ... public ISet<T> UnionWith(ISet<T> set) { ISet<T> unionSet = ... foreach (Element element in this) { unionSet.Add(element); } foreach (Element element in set) { unionSet.Add(element); } return unionSet; } }

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• Some basic UML questions

  - by devoured elysium

  What does it mean when you have something as the following picture? Each Customer has none, one or more Orders while each Order has only one Customer? And in relationship to the following one: What does the black diamond mean in this context? How is that black diamond called? Thanks

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• What is the problem with this Java code dealing with Generics?

  - by devoured elysium

  interface Addable<E> { public E add(E x); public E sub(E y); public E zero(); } class SumSet<E extends Addable> implements Set<E> { private E element; public SumSet(E element) { this.element = element; } public E getSum() { return element.add(element.zero()); } } It seems that element.add() doesn't return an E extends Addable but rather an Object. Why is that? Has it anything to do with Java not knowing at run-time what the object types really are, so it just assumes them to be Objects(thus requiring a cast)? Thanks

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• Fitch Format Proofs - any resources around?

  - by devoured elysium

  I am currently studying Fitch Format first order logic proofs. My lecturer follows closely Language, Proof and Logic by Jon Barwise. I am trying to do some proofs but I am having some trouble getting to understand how to do these proofs. As I have already read what Language Proof and Logic has to offer, I'd like to know if there are any other books or resources around that use the Fitch format for their formal proofs. Plus, having solved exercises would be of great(!) help. Thanks

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• Question about cloning in Java

  - by devoured elysium

  In Effective Java, the author states that: If a class implements Cloneable, Object's clone method returns a field-by-field copy of the object; otherwise it throws CloneNotSupportedException. What I'd like to know is what he means with field-by-field copy. Does it mean that if the class has X bytes in memory, it will just copy that piece of memory? If yes, then can I assume all value types of the original class will be copied to the new object? class Point { private int x; private int y; @Override public Point clone() { return (Point)super.clone(); } } If what Object.clone() does is a field by field copy of the Point class, I'd say that I wouldn't need to explicitly copy fields x and y, being that the code shown above will be more than enough to make a clone of the Point class. That is, the following bit of code is redundant: @Override public Point clone() { Point newObj = (Point)super.clone(); newObj.x = this.x; //redundant newObj.y = this.y; //redundant } Am I right? I know references of the cloned object will point automatically to where the original object's references pointed to, I'm just not sure what happens specifically with value types. If anyone could state clearly what Object.clone()'s algorithm specification is (in easy language) that'd be great. Thanks

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• Converting a String to Color in Java

  - by devoured elysium

  In .NET you can achieve something like this: Color yellowColor = Color.FromName("yellow"); Is there a way of doing this in Java without having to resort to reflection? PS: I am not asking for alternative ways of storing/loading colors. I just want to know wherever it is possible to do this or not.

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• Domain Model and Contracts

  - by devoured elysium

  I am modelling a DVD Rental Store: A Client gives its clientNumber to the System. The System checks whenever the given clientNumber is valid. The Client gives the name of the DVD he wants to rent. ... n. ...I will later have to form an association between a new instance of "RentDVD" class concept to the current Client c. My Domain Model is something like: I've made the Contract for the first and second operations as: Preconditions: none Postconditions: there exists a Client c such that c.clientNumber = clientNumber. Now, I don't know if I should form an association between this Client c and the DVDStore(that I intend to use as front-end). If I don't make the association, how will I later be able to "reference" this same Client? Should I be making an association between Client and a different concept? Thanks

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• JFrame.setBackground() not working -- why?

  - by devoured elysium

  JFrame mainFrame = new JFrame(); mainFrame.setSize(100, 100); mainFrame.setBackground(Color.CYAN); mainFrame.setVisible(true); My intent is to create a window with a cyan background. What is wrong with this? My window doesn't get cyan, as I'd expect! Also, could anyone point out why I seem to have all the colors in duplicate (there's a Color.CYAN and a Color.cyan). Is there any difference at all between the two? Maybe the older one was a constant from before there were enums in Java and the second one is from the Enum? Thanks

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• Is it possible to put namespaces in Visual Studio UML?

  - by devoured elysium

  Is it possible? Something like this: being it of course, that instead of packages, it'd appear as namespace. Thanks!

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• Possible to do UML Diagrams in Visual C# and then have code generated from it?

  - by devoured elysium

  I'm using Visual Studio 2010 RC. Would it be possible that after doing my UML Diagrams, I could then generate classes with method stubs from it? Thanks

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• Designing a class in such a way that it doesn't become a "God object"

  - by devoured elysium

  I'm designing an application that will allow me to draw some functions on a graphic. Each function will be drawn from a set of points that I will pass to this graphic class. There are different kinds of points, all inheriting from a MyPoint class. For some kind of points it will be just printing them on the screen as they are, others can be ignored, others added, so there is some kind of logic associated to them that can get complex. How to actually draw the graphic is not the main issue here. What bothers me is how to make the code logic such that this GraphicMaker class doesn't become the so called God-Object. It would be easy to make something like this: class GraphicMaker { ArrayList<Point> points = new ArrayList<Point>(); public void AddPoint(Point point) { points.add(point); } public void DoDrawing() { foreach (Point point in points) { if (point is PointA) { //some logic here else if (point is PointXYZ) { //...etc } } } } How would you do something like this? I have a feeling the correct way would be to put the drawing logic on each Point object (so each child class from Point would know how to draw itself) but two problems arise: There will be kinds of points that need to know all the other points that exist in the GraphicObject class to know how to draw themselves. I can make a lot of the methods/properties from the Graphic class public, so that all the points have a reference to the Graphic class and can make all their logic as they want, but isn't that a big price to pay for not wanting to have a God class?

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• Returning a ReadOnlyCollection from a method with an IList return type

  - by devoured elysium

  Here I have the following bit of code: private IList<IState> _states = new List<IState>(); private ReadOnlyCollection<IState> _statesViewer; public IList<IState> States { get { return _statesViewer; } } Generally it is preferable to return interfaces than the concrete classes themselves, but in this case, shouldn't I set as the return type of the States property a ReadOnlyCollection? Any user of my library will think it is possible to anything you can do with an IList if I set it as so, and that means adding elements. That is not true and I'm definitely breaking the contract exposing it as an IList. Am I right with this view or there is something else I am missing here?

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