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• Creating Dependencies Only to be able to Unit Test

  - by arin

  I just created a Manager that deals with a SuperClass that is extended all over the code base and registered with some sort of SuperClassManager (SCM). Now I would like to test my Manager that is aware of only the SuperClass. I tried to create a concrete SCM, however, that depends on a third party library and therefore I failed to do that in my jUnit test. Now the option is to mock all instances of this SCM. All is good until now, however, when my Manager deals with the SCM, it returns children of the SuperClass that my Manager does not know or care about. Nevertheless, the identities of these children are vital for my tests (for equality, etc.). Since I cannot use the concrete SCM, I have to mock the results of calls to the appropriate functions of the SCM, however, this means that my tests and therefore my Manager need to know and care about the children of the SuperClass. Checking the code base, there does not seem to be a more appropriate location for my test (that already maintains the appropriate real dependencies). Is it worth it to introduce unnecessary dependencies for the sake of unit testing?

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• Java - Class type from inside static initialization block

  - by DutrowLLC

  Is it possible to get the class type from inside the static initialization block? This is a simplified version of what I currently have:: class Person extends SuperClass { String firstName; static{ // This function is on the "SuperClass": // I'd for this function to be able to get "Person.class" without me // having to explicitly type it in but "this.class" does not work in // a static context. doSomeReflectionStuff(Person.class); // IN "SuperClass" } } This is closer to what I am doing, which is to initialize a data structure that holds information about the object and its annotations, etc... Perhaps I am using the wrong pattern? public abstract SuperClass{ static void doSomeReflectionStuff( Class<?> classType, List<FieldData> fieldDataList ){ Field[] fields = classType.getDeclaredFields(); for( Field field : fields ){ // Initialize fieldDataList } } } public abstract class Person { @SomeAnnotation String firstName; // Holds information on each of the fields, I used a Map<String, FieldData> // in my actual implementation to map strings to the field information, but that // seemed a little wordy for this example static List<FieldData> fieldDataList = new List<FieldData>(); static{ // Again, it seems dangerous to have to type in the "Person.class" // (or Address.class, PhoneNumber.class, etc...) every time. // Ideally, I'd liken to eliminate all this code from the Sub class // since now I have to copy and paste it into each Sub class. doSomeReflectionStuff(Person.class, fieldDataList); } }

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• C++ polymorphism, function calls

  - by moai

  Okay, I'm pretty inexperienced as a programmer, let alone in C++, so bear with me here. What I wanted to do was to have a container class hold a parent class pointer and then use polymorphism to store a child class object. The thing is that I want to call one of the child class's functions through the parent class pointer. Here's a sort of example of what I mean in code: class SuperClass { public: int x; } class SubClass : public SuperClass { public: void function1() { x += 1; } } class Container { public: SuperClass * alpha; Container(SuperClass& beta) { alpha = beta; } } int main() { Container cont = new Container(new SubClass); } (I'm not sure that's right, I'm still really shaky on pointers. I hope it gets the point across, at least.) So, I'm not entirely sure whether I can do this or not. I have a sneaking suspicion the answer is no, but I want to be sure. If someone has another way to accomplish this sort of thing, I'd be glad to hear it.

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• OOP design issue: Polymorphism

  - by Graham Phillips

  I'm trying to solve a design issue using inheritance based polymorphism and dynamic binding. I have an abstract superclass and two subclasses. The superclass contains common behaviour. SubClassA and SubClassB define some different methods: SubClassA defines a method performTransform(), but SubClassB does not. So the following example 1 var v:SuperClass; 2 var b:SubClassB = new SubClassB(); 3 v = b; 4 v.performTransform(); would cause a compile error on line 4 as performTransform() is not defined in the superclass. We can get it to compile by casting... (v as SubClassA).performTransform(); however, this will cause a runtime exception to be thrown as v is actually an instance of SubClassB, which also does not define performTransform() So we can get around that by testing the type of an object before casting it: if( typeof v == SubClassA) { (cast v to SubClassA).performTransform(); } That will ensure that we only call performTransform() on v's that are instances of SubClassA. That's a pretty inelegant solution to my eyes, but at least its safe. I have used interface based polymorphism (interface meaning a type that can't be instantiated and defines the API of classes that implement it) in the past, but that also feels clunky. For the above case, if SubClassA and SubClassB implemented ISuperClass that defined performTransform, then they would both have to implement performTransform(). If SubClassB had no real need for a performTransform() you would have to implement an empty function. There must be a design pattern out there that addresses the issue.

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• Why can't sub-packages see package private classes?

  - by Polaris878

  Okay so, I have this project structure: package A.B class SuperClass (this class is marked package private) package A.B.C class SubClass (inherits from super class) I'd rather not make SuperClass publicly visible... It is really just a utility class for this specific project (A.B). It seems to me that SubClass should be able to see SuperClass, because package A.B.C is a subpackage of A.B... but this is not the case. What would be the best way to resolve this issue? I don't think it makes sense to move everything in A.B.C up to A.B or move A.B down to A.B.C... mainly because there will probably be an A.B.D which inherits from stuff in A.B as well... I'm a bit new to Java, so be nice :D (I'm a C++ and .NET guy)

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• More than one profile in Django?

  - by JPC

  Is it possible to use Django's user authentication features with more than one profile? Currently I have a settings.py file that has this in it: AUTH_PROFILE_MODULE = 'auth.UserProfileA' and a models.py file that has this in it: from django.db import models from django.contrib.auth.models import User class UserProfileA(models.Model): company = models.CharField(max_length=30) user = models.ForeignKey(User, unique=True) that way, if a user logs in, I can easily get the profile because the User has a get_profile() method. However, I would like to add UserProfileB. From looking around a bit, it seems that the starting point is to create a superclass to use as the AUTH_PROFILE_MODULE and have both UserProfileA and UserProfileB inherit from that superclass. The problem is, I don't think the get_profile() method returns the correct profile. It would return an instance of the superclass. I come from a java background (polymorphism) so I'm not sure exactly what I should be doing. Thanks!

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• Does code in the constructor add to code in subclass constructors?

  - by Jeremy Rudd

  Does code in the constructor add to code in subclass constructors? Or does the subclass's constructor override the superclass? Given this example superclass constructor: class Car{ function Car(){ trace("CAR") } } ...and this subclass constructor: class FordCar extends Car{ function FordCar(){ trace("FORD") } } When an instance of FordCar is created, will this trace "Car" and "Ford" ??

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• class inheretence of a attribute which is itself a class

  - by alex

  i have a class which inherets a attribute from a super-class. this attribute is a class itself. class classA(superClass): def func(self,x): if self.attributeB is None: do somthing and in the other class i have class superClass: self.attributB = classB() i get the error AttributeError: class classA has no attribute 'attributeB' when i access the attribute like i showed but if on command line i can see it works, x = classA() x.attributeB is None True so the test works. whats going on in the above code?

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• Why should I call self=[super init]

  - by Michael

  Let's say I create my class and its init method. Why should I call and return value of superclass init assigned to self? Which cases it covers? I would appreciate examples why would I need it for Cocoa superclass and non-Cocoa.

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• Strategies for invoking subclass methods on generic objects

  - by Brad Patton

  I've run into this issue in a number of places and have solved it a bunch of different ways but looking for other solutions or opinions on how to address. The scenario is when you have a collection of objects all based off of the same superclass but you want to perform certain actions based only on instances of some of the subclasses. One contrived example of this might be an HTML document made up of elements. You could have a superclass named HTMLELement and subclasses of Headings, Paragraphs, Images, Comments, etc. To invoke a common action across all of the objects you declare a virtual method in the superclass and specific implementations in all of the subclasses. So to render the document you could loop all of the different objects in the document and call a common Render() method on each instance. It's the case where again using the same generic objects in the collection I want to perform different actions for instances of specific subclass (or set of subclasses). For example (an remember this is just an example) when iterating over the collection, elements with external links need to be downloaded (e.g. JS, CSS, images) and some might require additional parsing (JS, CSS). What's the best way to handle those special cases. Some of the strategies I've used or seen used include: Virtual methods in the base class. So in the base class you have a virtual LoadExternalContent() method that does nothing and then override it in the specific subclasses that need to implement it. The benefit being that in the calling code there is no object testing you send the same message to each object and let most of them ignore it. Two downsides that I can think of. First it can make the base class very cluttered with methods that have nothing to do with most of the hierarchy. Second it assumes all of the work can be done in the called method and doesn't handle the case where there might be additional context specific actions in the calling code (i.e. you want to do something in the UI and not the model). Have methods on the class to uniquely identify the objects. This could include methods like ClassName() which return a string with the class name or other return values like enums or booleans (IsImage()). The benefit is that the calling code can use if or switch statements to filter objects to perform class specific actions. The downside is that for every new class you need to implement these methods and can look cluttered. Also performance could be less than some of the other options. Use language features to identify objects. This includes reflection and language operators to identify the objects. For example in C# there is the is operator that returns true if the instance matches the specified class. The benefit is no additional code to implement in your object hierarchy. The only downside seems to be the lack of using something like a switch statement and the fact that your calling code is a little more cluttered. Are there other strategies I am missing? Thoughts on best approaches?

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• Building Dynamic Classes in Objective C

  - by kjell_

  I'm a somewhat competent ruby programmer. Yesterday I decided to finally try my hand with Apple's Cocoa frameworks. Help me see things the ObjC way? I'm trying to get my head around objc_allocateClassPair and objc_registerClassPair. My goal is to dynamically generate a few classes and then be able to use them as I would any other class. Does this work in Obj C? Having allocated and registered class A, I get a compile error when calling [[A alloc] init]; (it says 'A' Undeclared). I can only instantiate A using runtime's objc_getClass method. Is there any way to tell the compiler about A and pass it messages like I would NSString? A compiler flag or something? I have 10 or so other classes (B, C, …), all with the same superclass. I want to message them directly in code ([A classMethod], [B classMethod], …) without needing objc_getClass. Am I trying to be too dynamic here or just botching my implementation? It looks something like this… NSString *name = @"test"; Class newClass = objc_allocateClassPair([NSString class], [name UTF8String], 0); objc_registerClassPair(newClass); id a = [[objc_getClass("A") alloc] init]; NSLog(@"new class: %@ superclass: %@", a, [a superclass]); //[[A alloc] init]; blows up.

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• Python: Class factory using user input as class names

  - by Sano98

  Hi everyone, I want to add class atttributes to a superclass dynamically. Furthermore, I want to create classes that inherit from this superclass dynamically, and the name of those subclasses should depend on user input. There is a superclass "Unit", to which I can add attributes at runtime. This already works. def add_attr (cls, name, value): setattr(cls, name, value) class Unit(object): pass class Archer(Unit): pass myArcher = Archer() add_attr(Unit, 'strength', 5) print "Strenght ofmyarcher: " + str(myArcher.strength) Archer.strength = 2 print "Strenght ofmyarcher: " + str(myArcher.strength) This leads to the desired output: Strenght ofmyarcher: 5 Strenght ofmyarcher: 2 But now I don't want to predefine the subclass Archer, but I'd rather let the user decide how to call this subclass. I've tried something like this: class Meta(type, subclassname): def __new__(cls, subclassname, bases, dct): return type.__new__(cls, subclassname, Unit, dct) factory = Meta() factory.__new__("Soldier") but no luck. I guess I haven't really understood what new does here. What I want as a result here is class Soldier(Unit): pass being created by the factory. And if I call the factory with the argument "Knight", I'd like a class Knight, subclass of Unit, to be created. Any ideas? Many thanks in advance! Bye -Sano

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• Why does Java's invokevirtual need to resolve the called method's compile-time class?

  - by Chris

  Consider this simple Java class: class MyClass { public void bar(MyClass c) { c.foo(); } } I want to discuss what happens on the line c.foo(). At the bytecode level, the meat of c.foo() will be the invokevirtual opcode, and, according to the documentation for invokevirtual, more or less the following will happen: Look up the foo method defined in compile-time class MyClass. (This involves first resolving MyClass.) Do some checks, including: Verify that c is not an initialization method, and verify that calling MyClass.foo wouldn't violate any protected modifiers. Figure out which method to actually call. In particular, look up c's runtime type. If that type has foo(), call that method and return. If not, look up c's runtime type's superclass; if that type has foo, call that method and return. If not, look up c's runtime type's superclass's superclass; if that type has foo, call that method and return. Etc.. If no suitable method can be found, then error. Step #3 alone seems adequate for figuring out which method to call and verifying that said method has the correct argument/return types. So my question is why step #1 gets performed in the first place. Possible answers seem to be: You don't have enough information to perform step #3 until step #1 is complete. (This seems implausible at first glance, so please explain.) The linking or access modifier checks done in #1 and #2 are essential to prevent certain bad things from happening, and those checks must be performed based on the compile-time type, rather than the run-time type hierarchy. (Please explain.)

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• Properly populating tables in an Object Relational database

  - by chaosTechnician

  I've got a homework assignment that requires that I use Oracle 10g Express to implement an Object Relational database to track phone billing data. I have a superclass of Communications with subclasses of Call, Text, and Data. I'm hitting a snag with properly populating these tables so that I can find the appropriate data in the various tables. My Types and Tables are declared as such: create type CommunicationType as object ( -- column names here ) not final; create type CallType under CommunicationType ( -- column names here ); create type TextType under CommunicationType ( -- column names here ); create type DataType under CommunicationType ( -- column names here ); create table Communications of CommunicationType ( -- Primary and Foreign key constraints here ); create table Calls of CallType; create table Texts of TextType; create table Datas of DataType; When I try to insert data into one of the subclasses, its entry doesn't appear in the superclass. Likewise if I insert into the superclass, it doesn't show up in the appropriate subclass. For example, insert into Calls values (CallType( -- Values -- )); doesn't show any data in Communications. Nor does insert into Communications values (CallType( -- Values -- )); show anything in Calls. What am I doing wrong?

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• Can ScalaCheck/Specs warnings safely be ignored when using SBT with ScalaTest?

  - by pdbartlett

  I have a simple FunSuite-based ScalaTest: package pdbartlett.hello_sbt import org.scalatest.FunSuite class SanityTest extends FunSuite { test("a simple test") { assert(true) } test("a very slightly more complicated test - purposely fails") { assert(42 === (6 * 9)) } } Which I'm running with the following SBT project config: import sbt._ class HelloSbtProject(info: ProjectInfo) extends DefaultProject(info) { // Dummy action, just to show config working OK. lazy val solveQ = task { println("42"); None } // Managed dependencies val scalatest = "org.scalatest" % "scalatest" % "1.0" % "test" } However, when I runsbt test I get the following warnings: ... [info] == test-compile == [info] Source analysis: 0 new/modified, 0 indirectly invalidated, 0 removed. [info] Compiling test sources... [info] Nothing to compile. [warn] Could not load superclass 'org.scalacheck.Properties' : java.lang.ClassNotFoundException: org.scalacheck.Properties [warn] Could not load superclass 'org.specs.Specification' : java.lang.ClassNotFoundException: org.specs.Specification [warn] Could not load superclass 'org.specs.Specification' : java.lang.ClassNotFoundException: org.specs.Specification [info] Post-analysis: 3 classes. [info] == test-compile == For the moment I'm assuming these are just "noise" (caused by the unified test interface?) and that I can safely ignore them. But it is slightly annoying to some inner OCD part of me (though not so annoying that I'm prepared to add dependencies for the other frameworks). Is this a correct assumption, or are there subtle errors in my test/config code? If it is safe to ignore, is there any other way to suppress these errors, or do people routinely include all three frameworks so they can pick and choose the best approach for different tests? TIA, Paul. (ADDED: scala v2.7.7 and sbt v0.7.4)

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• Naming methods that do the same thing but return different types

  - by Konstantin Ð.

  Let's assume that I'm extending a graphical file chooser class (JFileChooser). This class has methods which display the file chooser dialog and return a status signature in the form of an int: APPROVE_OPTION if the user selects a file and hits Open /Save, CANCEL_OPTION if the user hits Cancel, and ERROR_OPTION if something goes wrong. These methods are called showDialog(). I find this cumbersome, so I decide to make another method that returns a File object: in the case of APPROVE_OPTION, it returns the file selected by the user; otherwise, it returns null. This is where I run into a problem: would it be okay for me to keep the showDialog() name, even though methods with that name — and a different return type — already exist? To top it off, my method takes an additional parameter: a File which denotes in which directory the file chooser should start. My question to you: Is it okay to call a method the same name as a superclass method if they return different types? Or would that be confusing to API users? (If so, what other name could I use?) Alternatively, should I keep the name and change the return type so it matches that of the other methods? public int showDialog(Component parent, String approveButtonText) // Superclass method public File showDialog(Component parent, File location) // My method

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• Class hierarchy problem in this social network model

  - by Gerenuk

  I'm trying to design a class system for a social network data model - basically a link/object system. Now I have roughly the following structure (simplified and only relevant methods shown) class Data: "used to handle the data with mongodb" "can link, unlink data and also return other linked data" "is basically a proxy object that only stores _id and accesses mongodb on requests" "it looks like {_id: ..., _out: [id1, id2,...], _inc: [id3, id4, ...]}" def get_node(self, id) "create a new Data object from the underlying mongodb" "each data object can potentially create a reference object to new mongo data" "this is needed when the data returns the linked objects" class Node: """ this class proxies linking calls to .data it includes additional network logic operations whereas Data only contains a basic database solution """ def __init__(self, data): "the infrastructure realization is stored as composition by an included object data" "Node bascially proxies most calls to the infrastructure object data" def get_node(self, data): "creates a new object of class Object or Link depending on data" class Object(Node): "can have multiple connections to Link" class Link(Node): "has one 'in' and one 'out' connection to an Object" This system is working, however maybe wouldn't work outside Python. Note that after reading links Now I have two questions here: 1) I want to infrastructure of the data storage to be replacable. Earlier I had Data as a superclass of Node so that it provided the neccessary calls. But (without dirty Python tricks) you cannot replace the superclass dynamically. Is using composition therefore recommended? The drawback is that I have to proxy most calls (link, unlink etc). Any thoughts? 2) The class Node contains the common method .get_node which is used to built new Object or Link instances after reading out the data. Some attribute of data decided whether the object which is only stored by id should be instantiated as an Object or Link class. The problem here is that Node needs to know about Object and Link in advance, which seems dodgy. Do you see a different solution? Both Object and Link need to instantiate one of all possible types depending on what the find in their linked data. Are there any other ideas how to implement a flexible Object/Link structure where the underlying database storage is isolated?

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• ruby super keyword

  - by ash34

  Hi, From what I understand, 'super' keyword invokes a method with the same name as the current method in the superclass of the current class. Below in the autoload method, there is a call to 'super'. I would like to know in which superclass I would find a method with the same name or what does the call to 'super' do module ActiveSupport module Autoload ... def autoload(const_name, path = @@at_path) full = [self.name, @@under_path, const_name.to_s, path].compact.join("::") location = path || Inflector.underscore(full) if @@eager_autoload @@autoloads[const_name] = location end super const_name, location end .... end end module ActiveRecord extend ActiveSupport::Autoload ... autoload :TestCase autoload :TestFixtures, 'active_record/fixtures' end This code is from the rails master branch. Thanks much.

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• Must I call super when I implement -scrollViewDidScroll: of UIScrollViewDelegate in an UITableView?

  - by mystify

  I made a custom UITableView subclass and implemented this: - (void)scrollViewDidScroll:(UIScrollView *)scrollView { // scrolled... } Now, what I think is that UITableView may also love to get this message for some obvious reasons. However, when I don't forward that to super, for some reason, everything still works fine. Must I forward that guy to super? I mean...it's a delegate method implementation, but as far as I'm aware of, this would still override anything implemented in UITableView, or not? Edit: I see...the delegate could be anyone. Never mind about this. BUT: What I have such a thing in a superclass, and make a subclass. How would I even know that the superclass does implement that method and I must forward it to super?

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• Accessing super class function using subclass object

  - by bdhar

  I have an object for a subclass who is of it's superclass type. There is a overridden function in subclass which gets executed when called using the object. How to call the parent's function using the same object? Is there any way to achieve this? package supercall; public class Main { public static void main(String[] args) { SomeClass obj = new SubClass(); obj.go(); } } class SomeClass { SomeClass() { } public void go() { System.out.println("Someclass go"); } } class SubClass extends SomeClass { SubClass() { } @Override public void go() { System.out.println("Subclass go"); } } Consider the code above. Here it prints Subclass go . Instead I have to print Superclass go .

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• viewDidLoad never called in Sub-classed UIViewController

  - by Steve

  I've run into some trouble with loading a sub-classed UIViewController from a nib. My viewDidLoad function is never called. The super-class has no nib, but the sub-classes each have their own. i.e. @interface SuperClass : UIViewController { } @end @interface SubClass : SuperClass{ } @end @implementation SubClass - (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil { self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil]; if (self) { } return self; } - (void)viewDidLoad{ // Never called } The view is loaded from a nib as follows: SubClass *scvc = [[SubClass alloc] initWithNibName:@"SubClass" bundle:nil]; [self.navigationController pushViewController:scvc animated:YES]; [scvc release]; There is a nib file with this name and it has it's file owner's class set properly. viewDidLoad is not called in the child or super. Any ideas?

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• Java: Non-static nested classes and instance.super()

  - by Kiv

  I'm having a hard time wrapping my head around non-static nested classes in Java. Consider the following example, which prints "Inner" and then "Child". class Outer { class Inner { Inner() { System.out.println("Inner"); } } } public class Child extends Outer.Inner { Child(Outer o) { o.super(); System.out.println("Child"); } public static void main(String args[]) { new Child(new Outer()); } } I understand that instances of Inner always have to be associated with an Outer instance, and that that applies to Child too since it extends Inner. My question is what the o.super() syntax means - why does it call the Inner constructor? I've only seen a plain super(args) used to call the superclass constructor and super.method() to call the superclass version of an overridden method, but never something of the form instance.super().

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• Java Inheritance - instance variables overriding

  - by Gogi

  Why are Instance variables of a superclass not overidden in Inheritance ?

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• How to avoid overriding of methods in subclass in objective c.

  - by chethan

  Can anyone please guide me on how to avoid overriding of superclass methods in subclass in Objective-C, like the "final" concept in Java.

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• contain new elements of an "instance" in javascript

  - by iamnotmad

  Hi, so I know there are tons of ways to simulate inheritance and other OO features. I have chosen one to use for my project and am wondering if I can create an instance and add stuff to it and keep it contained (within braces). Consider the following: function BaseClass(){ <this.stuff here> } function SubClass(){ this.superClass = BaseClass(); this.superClass(); <this.other stuff here> } myObj = new SubClass(); so myObj is an instance of SubClass. I can add things to myObj like: myObj.blah = "funtimes"; What I would like is to be able to add stuff to the "instance" and keep it organized in braces much like the constructor. psuedo code like: myObj = new SubClass() { var blah = "funtimes" <more instance specific stuff here> } Is something like this possible? Thanks!

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