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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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  • 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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  • How do I define my own operators in the Io programming language?

    - by klep
    I'm trying to define my own operator in Io, and I'm having a hard time. I have an object: MyObject := Object clone do( lst := list() !! := method(n, lst at(n)) ) But when I call it, like this: x := MyObject clone do(lst appendSeq(list(1, 2, 3))) x !! 2 But I get an exception that argument 0 to at must not be nil. How can I fix?

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  • Encapsulating a Windows.Forms.Button

    - by devoured elysium
    I want to define a special kind of button that only allows two possible labels: "ON" and "OFF". I decided to inherit from a Windows.Forms.Button to implement this but now I don't know I how should enforce this rule. Should I just override the Text property like this? public override string Text { set { throw new InvalidOperationException("Invalid operation on StartStopButton!"); } } The problem I see with this is that I am breaking the contract that all buttons should have. If any code tries something like foreach (Button button in myForm) { button.Text = "123"; } they will get an Exception if I have any of my special buttons on the form, which is something that isn't expectable. First, because people think of properties just as "public" variables, not methods, second, because they are used to using and setting whatever they want to buttons without having to worry with Exceptions. Should I instead just make the set property do nothing? That could also lead to awkward results: myButton.Text = "abc"; MessageBox.Show(abc); //not "abc"! The general idea from the OO world is to in this kind of cases use Composition instead of inheritance. public class MySpecialButton : <Some class from System.Windows.Forms that already knows how to draw itself on forms> private Button button = new Button(); //I'd just draw this button on this class //and I'd then only show the fields I consider //relevant to the outside world. ... } But to make the Button "live" on a form it must inherit from some special class. I've looked on Control, but it seems to already have the Text property defined. I guess the ideal situation would be to inherit from some kind of class that wouldn't even have the Text property defined, but that'd have position, size, etc properties available. Upper in the hierarchy, after Control, we have Component, but that looks like a really raw class. Any clue about how to achieve this? I know this was a long post :( Thanks

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  • servlet ArrayList and HashMap problem witch result

    - by nonameplum
    Hi, I have that code List<Map<String, Object>> data = new ArrayList<Map<String, Object>>(); Map<String, Object> item = new HashMap<String, Object>(); data.clear(); item.clear(); int i = 0; while (i < 5){    item.put("id", i);    i++;    out.println("id: " + item.get("id"));    out.println("--------------------------");    data.add(item); } for(i=0 ; i<5 ; i++){    out.println("print data[" + i + "]" + data.get(i)); } Result of that is: id: 0 -------------------------- id: 1 -------------------------- id: 2 -------------------------- id: 3 -------------------------- id: 4 -------------------------- print data[0]{id=4} print data[1]{id=4} print data[2]{id=4} print data[3]{id=4} print data[4]{id=4} Why only last element is stored?

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  • One UI for two business objects

    - by JC
    I have an order edit and quote edit screen that are very similar. I want to try to avoid code like this: if (order is Order) SetupScreenForOrder(); if (order is Quote) SetupScreenForQuote(); But maintaining two screens is not good either. If I create some common interface between a Quote and Order then how do you deal with fields like OrderNumber or QuoteDate? What's the best way to handle this?

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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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  • Test if a method is an override?

    - by Water Cooler v2
    Is there a way to tell if a method is an override? For e.g. public class Foo { public virtual void DoSomething() {} public virtual int GimmeIntPleez() { return 0; } } public class BabyFoo: Foo { public override int GimmeIntPleez() { return -1; } } Is it possible to reflect on BabyFoo and tell if GimmeIntPleez is an override?

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  • NSPredicate (Core Data fetch) to filter on an attribute value being present in a supplied set (list)

    - by starbaseweb
    I'm trying to create a fetch predicate that is the analog to the SQL "IN" statement, and the syntax to do so with NSPredicate escapes me. Here's what I have so far (the relevant excerpt from my fetching routine): NSFetchRequest *request = [[[NSFetchRequest alloc] init] autorelease]; NSEntityDescription *entity = [NSEntityDescription entityForName: @"BodyPartCategory" inManagedObjectContext:_context]; [request setEntity:entity]; NSPredicate *predicate = [NSPredicate predicateWithFormat:@"(name IN %@)", [RPBodyPartCategory defaultBodyPartCategoryNames]]; [request setPredicate:predicate]; The entity "BodyPartCategory" has a string attribute "name". I have a list of names (just NSString objects) in an NSArray as returned by: [RPBodyPartCategory defaultBodyPartCategoryNames] So let's say that array has string such as {@"Liver", @"Kidney", @"Thyroid"} ... etc. I want to fetch all 'BodyPartCategory' instances whose name attribute matches one of the strings in the set provided (technically NSArray but I can make it an NSSet). In SQL, this would be something like: SELECT * FROM BodyPartCategories WHERE name IN ('Liver', 'Kidney', 'Thyroid') I've gone through various portions of the Predicate Programming Guide, but I don't see this simple use case covered. Pointers/help much appreciated!

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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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  • Write a program for a report derived from the data in the data file JEWELRY. The data is to be input

    - by Taylor
    here is the JEWELRY file 0011 Money_Clip 2.000 50.00 Other 0035 Paperweight 1.625 175.00 Other 0457 Cuff_Bracelet 2.375 150.00 Bracelet 0465 Links_Bracelet 7.125 425.00 Bracelet 0585 Key_Chain 1.325 50.00 Other 0595 Cuff_Links 0.625 525.00 Other 0935 Royale_Pendant 0.625 975.00 Pendant 1092 Bordeaux_Cross 1.625 425.00 Cross 1105 Victory_Medallion 0.875 30.00 Pendant 1111 Marquis_Cross 1.375 70.00 Cross 1160 Christina_Ring 0.500 175.00 Ring 1511 French_Clips 0.687 375.00 Other 1717 Pebble_Pendant 1.250 45.00 Pendant 1725 Folded_Pendant 1.250 45.00 Pendant 1730 Curio_Pendant 1.063 275.00 Pendant this is the program i have used #include <iostream> #include <string> #include <iomanip> #include <fstream> using namespace std; struct productJewelry { string name; double amount; int itemCode; double size; string group; }; int main() { // declare variables ifstream inFile; int count=0; int x=0; productJewelry product[50]; inFile.open("jewelry.txt"); // file must be in same folder if (inFile.fail()) cout << "failed"; cout << fixed << showpoint; // fixed format, two decimal places cout << setprecision(2); while (inFile.peek() != EOF) { // cout << count << " : "; count++; inFile>> product[x].itemCode; inFile>> product[x].name; inFile>> product[x].size; inFile>> product[x].amount; inFile>> product[x].group; // cout << product[x].itemCode << ", " << product[x].name << ", "<< product[x].size << ", " << product[x].amount << endl; x++; if (inFile.peek() == '\n') inFile.ignore(1, '\n'); } inFile.close(); string temp; bool swap; do { swap = false; for (int x=0; x<count;x++) { if (product[x].name>product[x+1].name) { //these 3 lines are to swap elements in array temp=product[x].name; product[x].name=product[x+1].name; product[x+1].name=temp; swap=true; } } } while (swap); for (x=0; x< count; x++) { //cout<< product[x].itemCode<<" "; //cout<< product[x].name <<" "; //cout<< product[x].size <<" "; //cout<< product[x].amount<<" "; //cout<< product[x].group<<" "<<endl; } system("pause"); // to freeze Dev-c++ output screen return 0; } // end main

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  • What's the consequence when Core Data detects an optimistic locking failure when trying to save?

    - by dontWatchMyProfile
    I get it: When a managed object context saves, the snapshots of all edited objects are compared against the values in the persistent store to see if the PS has changed since the snapshot was made. If it did change, then there's a conflict and optimistic locking failed, according to Apple. But now, what's the consequence of this? What happens next? What are my options in this case?

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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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  • 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 I 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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  • Java inheritance question

    - by user247866
    So I have 3 classes. Abstract class A Class B extends class A independent Class C In class D that contains the main method, I create a list of instances of class B List<B> b = method-call();` // the method returns a list of instances of class B Now in class C I have one method that is common to both A and B, and hence I don't want to duplicate it. I want to have one method that takes as input an instance of class A, as follows: public void some-method(LIst<A> a) However, when I do: C c = new C(). c. some-method(b) I get an error that some-method is not applicable for the argument List, instead it's expecting to get List. Is there a good way to fix this problem? Many thanks!

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  • How does Undo work?

    - by dontWatchMyProfile
    How does undo work? Does it copy all the managed objects every time any of the values change? Or does it only copy the actual changes together with an information which objects were affected? Is that heavy or lightweight?

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  • OOP beginner: classB extends classA. classA already object. method in classB needed.. etc.

    - by Yvo
    Hey guys, I'm learning myself to go from function based PHP coding to OOP. And this is the situation: ClassA holds many basic tool methods (functions). it's __construct makes a DB connection. ClassB holds specific methods based on a certain activity (extract widgets). ClassB extends ClassA because it uses some of the basic tools in there e.g. a database call. In a php file I create a $a_class = new ClassA object (thus a new DB connection). Now I need a method in ClassB. I do $b_class = new ClassB; and call a method, which uses a method from it's parent:: ClassA. In this example, i'm having ClassA 'used' twice. Onces as object, and onces via a parent:: call, so ClassA creates another DB connection (or not?). So what is the best setup for this basic classes parent, child (extend) situation? I only want to make one connection of course? I don't like to forward the object to ClassB like this $b_class = new ClassB($a_object); or is that the best way? Thanks for thinking with me, and helping :d

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  • Why are interfaces unusable in PHP?

    - by streetparade
    I mean an interface definition without defining the return type makes it unusable? This makes more Clear Interface run { public function getInteger(); } class MyString implements run { public function myNumber() { } public function getInteger() { return "Not a number"; } } In Java every Interface has a return type like Integer,String,Void I know that PHP is unfortunately a loosly typed Language but isnt there a Solution for that Problem? Is it Possible to defining a Interface with a Return type like Integer?

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