I have a custom type that is abstract.
As it seems that leads to it not getting its own block_prefix in the hierarchy.
So I thought I would put that into configureOptions.
But in the deriving classes I do occassionally also have to define configureOptions which then again leads to either overwriting the parent method which defeats the purpose. Or if I call it explicitly
with parent::configureOptions the system will put the custom prefix above (in the sense of "higher priority") the automatically generated prefix of the implementing class which I obviously do not want.
Is there a solution to this problem that is not "make the parent class not abstract"?
I say that because if possible I don't want to loose the enforcement of the contract given by the abstract parent-class.
EDIT: I realized that it was a false assumption I made that making the base class non-abstract would lead to the addition of the class name as block-prefix.
Related
I have a question regarding UML Class diagrams.
I know I can just use one name which refers to both sides but my question is:
Is it necessary to show association names at both sides of an association when it is uni directional?
Association ends are properties (i.e., "variables"). When a class owns a property and the property is unnamed, that could be a problem. In contrast, when an association owns an unnamed property, that's not really a problem. You don't need to specify a name for association-owned properties.
Here's an example. I've made MagicDraw show association-end properties as attributes as well, just to make a point:
Notice how theB shows up as a property in class A and at the end of the association with class B. That's because they are two different ways of showing the same property. (It's a special way of showing association-end properties that we normally don't turn on in the tool.) Also notice how class C has an unnamed property inside the box and at the end of the association with class A. Again, that's two different ways to show the same property. How would you implement that unnamed property in a programming language? That could be a problem, right?
Another thing to notice is that class B does not have an attribute called theA, and class A does not have an attribute called theC. That's because those properties are non-navigable and the associations own those properties.
Conflating navigability and property ownership has become deprecated in UML. Recently, the UML spec introduced "association dot notation" to indicate property ownership. (A dot at the end means the class owns the property.) Personally, I never had a problem with the conflation, and I hate the new dot notation. Many tools do not support it, and I think it's downright ugly. Moreover, a diagram that has no dots on it is ambiguous. You can't tell whether it was drawn before or after dots were introduced to the spec!
This is a simple questions. I have researched this questions in my notebooks and books and the internet but cant find an answer
Why would we override the default constructor by adding parameters to it?
You would create a constructor for a class to manipulate its member variables according to whatever other conditions as soon as it's created. I get the impression you don't actually know what a constructor is.
Many languages (like C++/C#/Java) automatically create default no-arguments constructor when none defined in the class explicitly.
When you create a constructor in a class with or without arguments usually compiler stop creating default auto-generated constructor (depending on language specification). This is done on assumption if you have some non default initialization than automatically generated one is likely to not create object in a state you would expect.
Since having constructor with arguments is natural way to create objects it is essentially lead to "removing" default auto-generated constructor which probably can be called "overriding default constructor".
I interface with two data stores, one of them is RDMS and the other one is LDAP. What I want to do is to have a hierarchy persisted using "superclass-table" in the RDBMS and "complete-table" in LDAP.
Is such a thing possible? That is, can you specify multiple inheritance strategies, separately for each data store in the *.orm files or am I forced to use a single inheritance strategy?
I couldn't find this information in the documentation of DataNucleus, they only thing I'm sure of is that you can put inheritance elements in an .orm file instead of the .jdo but that still doesn't answer my question...
The hierarchy is rather simple and consists of an abstract class and several subclasses like this:
abstract class Foo implements IFoo
{
...
}
class Foo1 extends Foo
{
...
}
class Foo2 extends Foo
{
...
}
...
I tried to configure inheritance in the two *.orm files AND in the .jdo file (having in mind that it's going to get overriden by the former) but I get an exception
Caused by: org.datanucleus.metadata.InvalidMetaDataException: Class "...Foo1..." has been specified with an inheritance strategy of "superclass-table", yet no superclass exists or none exists with its own table!
at org.datanucleus.metadata.AbstractClassMetaData.validateUserInputForInheritanceMetaData(AbstractClassMetaData.java:903)
at org.datanucleus.metadata.ClassMetaData.populate(ClassMetaData.java:214)
at org.datanucleus.metadata.MetaDataManager$1.run(MetaDataManager.java:2393)
at java.security.AccessController.doPrivileged(Native Method)
at org.datanucleus.metadata.MetaDataManager.populateAbstractClassMetaData(MetaDataManager.java:2387)
at org.datanucleus.metadata.MetaDataManager.populateFileMetaData(MetaDataManager.java:2224)
at org.datanucleus.jdo.metadata.JDOMetaDataManager.loadMetaDataForClass(JDOMetaDataManager.java:741)
at org.datanucleus.jdo.metadata.JDOMetaDataManager.getMetaDataForClassInternal(JDOMetaDataManager.java:353)
at org.datanucleus.jdo.metadata.JDOMetaDataManager$MetaDataRegisterClassListener.registerClass(JDOMetaDataManager.java:184)
at javax.jdo.spi.JDOImplHelper.registerClass(JDOImplHelper.java:376)
I then tried to remove the inheritance elements from the .jdo but the enhancer fails with the following message:
Class "...Foo1..." has been specified to use an inheritance strategy of "superclass-table", persisting to the table of class ...Foo..., however this class doesnt have a discriminator specified.
The individual configurations are correct (new-table with discriminator at base-class and superclass-table at subclasses for the first case and complete-table only at base-class for the second).
You can put that information in the orm file, yes, and indeed that does answer your question since you have one ORM file for RDBMS, and one for LDAP. So package-rdbms.orm, and package-ldap.orm, and then simply set persistence property "javax.jdo.option.Mapping" to either "rdbms" or "ldap". Simple
Are there any languages that allow changing the access modifier of a given member at runtime?
For example for hiding/showing information depending on the context where an object is being used.
Most languages can do this, but it often comes with a performance penalty. For example, you could change the accessibility of a private constructor in Java with the following.
Constructor constructor = MyClass.class.getDeclaredConstructor(paramTypes);
constructor.setAccessible(true);
MyClass instance = (MyClass)constructor.newInstance(params);
Look at the methods available on the class object in your favorite language and you'll see a number of ways to get at methods or fields, and once you have a handle on those, you can abuse them to your heart's content.
I've got a class called ArtificialIntelligenceBase from which you can create your own artificial intelligence configuration sending some variables to the constructor or you can make a class that inherits from ArtificialIntelligenceBase and in the constructor of this new class just call the function super() with the parameters of the configurations.
I've also created some examples of artificial intelligences in classes, AIPassive, AIAgressive and AIDefensive. Obviously all of them inherits from ArtificialIntelligenceBase.
The point is that there're only few public functions in the base class. The variables in the base class are read only and the non public functions are protected in case you need to apply some modifications on them when created another pre-defined AI.
You can also create another AI just calling the base class sending some parameters in the constructor like this: new ArtificialIntelligenceBase(param1, param2, param3, param4);
I've tought about make the classes as a singleton because the classes can never change and once setted, their variables never change.
The question is: Is the singleton the best pattern to do this? Because I'm not sure.
PD: You don't need to explain any patter, just mention the name and I'll search for how it works
PPD: I'm developing in AS3. Just in case it helps
Thanks
In general, singletons are evil. I don't see any reason in your case to use a singleton, either. It sounds like you're using your own version of a factory method pattern (using a constructor somehow?) or maybe a prototype (I don't know AS3 one bit), but if you're looking for other patterns a couple of other ones are abstract factory and builder.
You don't need to use the singleton pattern to limit yourself to using only one instance per type of class, though. It doesn't help avoid redundancy.