I need to return an exception that contains a list of exceptions. This is easy enough to do, but I'd like to know if there is a built-in Exception Class that does this as I'd hate to "roll my own" instead of following built-in, documented classes.
Thanks,
Larry
There is the InnerException property, but if you need more than that, you'll need to roll your own.
Related
I have created a Singleton class that handles my project texts. What is the appropriate name of a Singleton class like this?
TextManager?
TextHandler?
TextController?
Is there a difference in meaning of these names?
UPDATE:
The class stores the project text as xml and have a method for returning the correct text.
function getText(uid : String) : String
I suppose it doesn't deal with adding/removing/... (-> managing) the texts (maybe just loading), so it isn't a "real" Manager.
It also doesn't "control" the texts (something "You're only accessible from ...", "Return another value for that key if ...").
The class provides you with texts.
I suppose it's some Kind of localized text provider, right?
So why don't you call it LocalizedTextProvider?
I usually call something like this
TextUtility
or
TextHelper
the problem with 'handler' is that it implies some sort of event handling. Same thing with 'Controller', it has meaning in a different context.
I believe Controller is 'reserved' for the MVC model but I may be wrong. TextHandler and TextManager may be better but at least at the place I work, 'Manager' in a service/class is generally discouraged since it is assumed that every class 'manages' something (this may just be culture-specific, though).
I'd vote for TextHandler out of those three. It may also depend slightly on your programming language.
This actually sounds like a service or repository to me...
TextService or TextRepository? TextModel?
But let me back up a bit... the Singleton pattern is a pretty bad way of accessing something like this. Just google "Singleton pattern problems" if you want to see what I am talking about. Plus, in AS3, you don't have private constructors so you can't implement the Singleton pattern in a pure way.
Instead, I really prefer composition via "Inversion of Control" (IoC) containers. There are plenty of them out there for ActionScript. They can be really lightweight but they decouple your components in a really elegant way.
Sorry to inject my thoughts here... ymmv :)
EDIT -- More on eliminating Singleton pattern
I have written about several strategies on eliminating singletons in your code. This article was written for C#, but all the same principles apply. In that article, I DON't talk explicitly about IoC containers.
Here is a pretty good article about IoC in Flex. In addition, several frameworks give you IoC capabilities:
Swiz
Robot Legs
fling
Cairngorm
flex-ioc
All three of the names you proposed can all be interpreted in the same way. Some people prefer handlers while others might say controllers... it really is a matter of semantics. Whatever convention you choose to adopt just be consistent. The common notion that you should capture though is that the class which you are describing is not doing anything. It should only be in charge of delegating, since that's what managers do to employees and controllers do in the classic MVC paradigm.
As I usually have Handler in the event/message handling context. Controller for actions and MVC stuff, I would go with something different:
TextResources.get(key)
I18n.get(key) (if your class is in fact used for internationalisation)
I usually reserve Helpers for classes allowing to simply transform some data into something to be used in the view.
TextCache? Sounds like you are just using it to store and retrieve data...
Why not : ProjectNameTexts
FooTexts.getInstance().getText('hello_world');
I read a thread on this topic on this very forum which listed some reasons to use custom exceptions but none of them really seemed strong reasons (can't remember the reasons now).
So why would you use custom exceptins? In particular, I have never understood the decision making process between using a standard or custom exception to indicate a shopping basket is null (I think a custom one is used as an empty collection is not exceptional and this is a business process thing). More clarification is needed, however.
Thanks
Here is my take:
If any of the standard exceptions do not match the exceptional situation, create a custom exception
If there is additional information that you need to pass in to the exception, create a custom exception
If there is meaning to having your own exception class, create a custom exception (that is, other developers will benefit from being able to catch it)
In regards to things like null arguments - I would never use a custom exception. The NullArgumentException (.NET) / IllegalArgumentException (Java) is perfectly satisfactory.
Jared Par has a blog entry about this, here.
Here is the problem statement: Calling a setter on the object should result in the object to change to an object of a different class, which language can support this?
Ex. I have a class called "Man" (Parent Class), and two children namely "Toddler" and "Old Man", they are its children because they override a behaviour in Man called as walk. ( i.e Toddler sometimes walks using both his hands and legs kneeled down and the Old man uses a stick to support himself).
The Man class has a attribute called age, I have a setter on Man, say setAge(int ageValue). I have 3 objects, 2 toddlers, 1 old-Man. (The system is up and running, I guess when we say objects it is obvious). I will make this call, toddler.setAge(80), I expect the toddler to change to an object of type Old Man. Is this possible? Please suggest.
Thanks,
This sounds to me like the model is wrong. What you have is a Person whose relative temporal grouping and some specific behavior changes with age.
Perhaps you need a method named getAgeGroup() which returns an appropriate Enum, depending on what the current age is. You also need an internal state object which encapsulates the state-specific behavior to which your Person delegates behavior which changes with age.
That said, changing the type of an instantiated object dynamically will likely only be doable only with dynamically typed languages; certainly it's not doable in Java, and probably not doable in C# and most other statically typed languages.
This is a common problem that you can solve using combination of OO modelling and design patterns.
You will model the class the way you have where Toddler and OldMan inherit from Man base class. You will need to introduce a Proxy (see GoF design pattern) class as your access to your Man class. Internally, proxy hold a man object/pointer/reference to either Toddler or OldMan. The proxy will expose all the interfaces that is exposed by Man class so that you can use it as it is and in your scenario, you will implement setAge similar to the pseudo code below:
public void setAge(int age)
{
if( age > TODDLER_MAX && myMan is Toddler)
myMan = new OldMan();
else
.....
myMan.setAge(age);
}
If your language does not support changing the classtype at runtime, take a look at the decorator and strategy patterns.
Objects in Python can change their class by setting the __class__ attribute. Otherwise, use the Strategy pattern.
I wonder if subclassing is really the best solution here. A property (enum, probably) that has different types of people as its possible values is one alternative. Or, for that matter, a derived property or method that tells you the type of person based on the age.
Javascript can do this. At any time you can take an existing object and add new methods to it, or change its existing methods. This can be done at the individual object level.
Douglas Crockford writes about this in Classical Inheritance in JavaScript:
Class Augmentation
JavaScript's dynamism allows us to add
or replace methods of an existing
class. We can call the method method
at any time, and all present and
future instances of the class will
have that method. We can literally
extend a class at any time.
Inheritance works retroactively. We
call this Class Augmentation to avoid
confusion with Java's extends, which
means something else.
Object Augmentation
In the static object-oriented
languages, if you want an object which
is slightly different than another
object, you need to define a new
class. In JavaScript, you can add
methods to individual objects without
the need for additional classes. This
has enormous power because you can
write far fewer classes and the
classes you do write can be much
simpler. Recall that JavaScript
objects are like hashtables. You
can add new values at any time. If the
value is a function, then it becomes a
method.
Common Lisp can: use the generic function CHANGE-CLASS.
I am surprised no one so far seemed to notice that this is the exact case for the State design pattern (although #Fadrian in fact described the core idea of the pattern quite precisely - without mentioning its name).
The state pattern is a behavioral software design pattern, also known as
the objects for states pattern. This pattern is used in computer
programming to represent the state of an object. This is a clean way for an
object to partially change its type at runtime.
The referenced page gives examples in Java and Python. Obviously it can be implemented in other strongly typed languages as well. (OTOH weakly typed languages have no need for State, as these support such behaviour out of the box.)
I just realize some of my classes have no members. It has several public functions and maybe private functions and everything is passes through params. I realize functional programmers do this all the time but is this class considered special if it access nothing outside of the class and only uses its params for reading (except for out params and return values)?
I know this class can be static but static classes can modify outside variables. I want to know if this is a technique or maybe if a language may give additional benefits for writing it this way and etc.
-edit- This is looking like a wiki so lets make it one.
It is just called "stateless". Nothing really special about it.
There is nothing wrong with a class that has no members; controllers do this very frequently.
Yes, you could go static, but by not being static you allow for inheritance from your memberless class, which could add members along the way, if you so desired.
If there are no members, then there is no need for a class other than having a namespace. If you were programming in Python, then you would just put those methods into a module and don't bother with a class. If you are working in Java, then a a class is a must. If you are working in C++, it's up to you - but maybe you should consider using just a namespace, instead of a class, to make it less confusing.
Yes, this makes the class completely thread safe and thus no locking is required. To me, that is a fantastic attribute.
Sane programming languages allow you to define functions outside of classes when the functions do not require any persistent data - if you can define it in an appropriate namespace, all the better. If your language does not allow that, at least define them in a static class so it's clear that no state is accessed or mutated. Overall, though, this reminds me of an excellent article on the illogical abuse of classes in the name of "pure OOP".
I'd make the class static. I don't see what advantage it would give to keep it non-static. But then again - I'm a .NET developer, not Java. The languages are close, but there are many subtle differences I'm not aware of.
Remember that all methods of your class (even stateless) have one special variable -- pointer/reference to object - this (self, whatever) for which they are applied to.
Thus it is perfect sense in such stateless class if its methods could be overridden: in this case you have to have class to provide dispatching by this.
(Of course it's just emulating of first-class functions, so if your language already has ones it's no sense in this technique.)
At the moment I can't imagine why would you need stateless class without any virtual method.
Unless you want to have nice auto-complete in your IDE by typing objectName and dot :)
its simple class there is no specialty in it.
But i dont understand what is the use of having public or private methods when there in no member in it. because member methods are those which acts on particular instance's state.
Yes you can have static methods in it.
Does anyone know of a program or plug-in or anything that I can find out what are all the exceptions any method may throw?
I think JAVA has this build in if I'm not mistaken. Where the compiler tells you what exceptions this method will throw.
Does the same exist for .NET?
Thanks
Edit: After searching around more, I wish there was tool like Object Explorer, except for Exceptions. You select the class or method and it lists the exceptions, at that level, which are thrown by the class. The tool links provided are a great start. Thanks!
I don't know if this is exactly what you are looking for, but:
http://www.red-gate.com/Products/Exception_Hunter/index.htm
Note: I've never used the product, and I don't work for Red Gate, I just remember seeing it advertised before.
You can see this information with intellisense in Visual Studio. When you highlight a method name in the intellisense list, its description should contain a list of exceptions at the bottom. This information is added by properly commenting your methods and classes. If you are using a library that is not part of the framework, then you will only get this information if the developers of the library appropriately commented their code.
.NET doesn't require or permit each method to state which exceptions it throws. As I recall, it was felt that this would lead most developers to simply state "throws Exception".