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Question might be silly for experts but please help me with pointers if it is already solved somewhere.
Interview Question : "Design class diagram in best possible way"
You need to design a game "SuperHeroes".
Super hero examples are Batman, Spider-Man, Thor, Hal Jordan, Wonder Woman, Captain America .... n
Spiderman can jump, crawl, generateFire ....n
Batman can jump, crawl, fly .... n
Thor can swim, fly .... n
There can be millions of behaviour.
There can be millions of Super heroes.
Some have few behaviours common in them and some specific to hero.
Design should be flexible enough to add behaviours to the super heroes
Important point to focus was told that "System should be scalable"
I tried twisting decorator pattern to accommodate problem requirements but was failing at many places, also I have to make many interfaces for this, so scalability was questionable.
I tried another approach as Writing all behaviours in one class(If require will classify behaviours in respective classes, kind of utility class which will have all implementations of behaviours). and an Spiderman class which will have list of allowable Behaviours(kind of enum). and it is allowed to call methods from behaviour utility only if such behaviour is allowed in list. I think it is not a good approach.
Please help me with best way to achieve this.
If I understood the question correctly, the problem could be solved with the mixin pattern; however, multiple inheritance is required for a straightforward implementation, which is not available in Java. The subject is discussed in this question.
In games it is pretty easy to get a very huge inheritance tree up to the point, where it is very difficult, if not impossible to add a new entity with a different behaviour. To solve this, something called the Entity Component System is used. It is very flexible, does not limit you to inheritance and is commonly used in larger games.
There is also a follow-up article that describes a specific implementation, and has examples on how it can be used in different situations.
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Most of the people says that abstraction is hiding something and showing only functionality to the user. Can anyone explain me what are all the things you are hiding and what are all the things you are showing?? please don't explain with the examples of animal, engine, vehicle.
I think this is a case where a concrete example would help a lot.
HashMap has an internal structure for handling hash collisions, which is an implementation of a singly-linked list. Now, do you know how that internal structure works, what it's called, what its fields are called, etc? More importantly, do you care, so long as the HashMap "just works"?
If the answer to both of those is "no" — which is what it should be for anything other than curiosity/learning purposes — then those details have been hidden from you and exposed via the abstraction of Map's interface.
The result is a class that's easier for you to reason about (because you have less to learn), and easier for the library maintainers to maintain (because they don't need to worry about a change they make breaking your code, so long as they still abide by the interface).
Abstraction is an overloaded term.
Abstraction, in object oriented languages, basically means leaving away unnecessary details when modeling real world objects. You could also think of it as a simplifying process.
Abstraction, in computer science as a whole, also means hiding complexity by providing some sort of simpler interface. Your question seems to aim at "data abstraction" which means hiding the exact way data is represented with an abstraction layer. This could be e.g. the Number data type in databases. You just know it is a number, but not how it is stored on disk.
Abstraction sometimes is used equivalently to encapsulation, too.
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I'm using Java to do some complicated calculations, and have a lot of classes that need access to a lot of the same variables. These variables are set at different stages of the calculations, in different classes. The problem is that my code is getting quite messy as I am being forced to pass the same parameters to a lot of different methods.
I am looking for peoples thoughts on what the best approach here would be? One idea I have is to make a superclass with all these variables set in it and extend this class everywhere it is needed.
Another option is to pass an object holding all this information around from method to method but this seems overly complex.
Neither of these solutions feel like the cleanest approach to me. Any thoughts or suggestions of design patterns/ideas that may help me are appreciated. Thanks for your help.
I'm going to suggest that using a Wrapper object is the best way to do this. Make sure all fields are immutable (final keyword in Java). Use a Builder or Prototype pattern to create new objects to return.
How about using a Singleton? That way you'd have global access to it without passing any instances around and all the variables will be under one roof reducing messiness.
I would recommand to separate the problem world (i.e. the variables) from the algorithms (i.e. calculations) in separate classes. The algorithms would get passed in the problem world, and modify it accordingly. This can be seen as an implementation of the Visitor Pattern.
Depending on the complexity (number of variables, number of algorithms, uncernity of solution path), you could also implement a Black Board Architecture. But I think that would be an overkill, if you're not doing something in artificial intelligence...
If there are a lot of values to be passed around, perhaps an in-memory database would be an appropriate solution. A lot of databases these days offer an in-memory engine, e.g. MariaDB.
Make a superclass of subclasses then refer to those subclasses of the superclass everytime you need to pull information
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I currently have several "manager" classes in a project I am working on but have seen a lot of things that advise you to not use manager classes but don't seem to provide any alternatives in my situation. I have a ClickManager which contains a map of "clickable" objects and a ConfigManager which is responsible for loading and saving config files as the config class comes from an API I am using and is too stupid to load itself.
What are some alternatives to using "manager" in these cases?
Ward Cunningham once said (1) that every programmer should have a dictionary and a thesaurus on his or her desk. There's also a saying that there are only two hard problems in computer science: cache invalidation and naming things. (2)
The point is that naming things is important, and it's hard, and it's often neglected. This is why there are classes named Data and Manager littered around many code bases.
There are at least two potential things going on here. One is that the class is doing something reasonable, and it just needs to have a good, concise, descriptive name applied to it. For example, with ClickManager, does it dispatch events to the clickable objects? If so, maybe it's a Dispatcher. Does it lay out the clickable objects? Maybe it's a Positioner. Does it contain the clickable objects (as Erwin Bolwidt suggested)? Maybe it's a Container. Does it execute something in response to a click? Maybe it's an InteractiveCommand. It's sometimes helpful to think more specifically about what a class is doing in order to come up with a good name.
Another possibility is that the class has too many responsibilities, that is, it violates the Single Responsibility Principle. This is often the reason that something is hard to name, because it does a bunch of different stuff. Suppose the class simultaneously contains clickable objects, dispatches events to them, positions them, and executes commands. It's no wonder that it's hard to come up with a name other than Manager because it's doing all of these related, but independent functions. (Note that in many UI toolkits, these responsibilities have been separated into different classes.)
If this is the case it might be advisable to do some refactoring of a big Manager class into smaller classes, each of which has fewer (or one) responsibilities. It should be easier to come up with better names for those classes.
(1) I think it was at an OOPSLA about ten years ago.
(2) And off-by-one errors.
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My project classes are quickly approaching large numbers of lines into the thousands. Is it good programming practice to divide the classes Into smaller classes even if they do the same thing? After all I'd hate to create communication caller functions for the same object.
It is a good programming practice to split up your code so you (and others) don't get lost.
Split it into methods/functions/procedures, classes and packages by meaning, not by size alone.
If several classes do the same thing, have you thought about using inheritance? Don't duplicate code, it makes maintenance harder (and is a waste).
For Java, interfaces and abstract classes can also improve legibility and structure of your code; use with moderation. Many Java IDEs come with handy "refactoring" functionalities which allow you to restructure your code easier and cleaner than copy/paste would be.
( Possibly related topic: "how do you organize your programming work" how do you organize your programming work )
As a rule, each class should have one responsibility that you can clearly state. If you can't state a single purpose for a class, or the narrowest purpose you can define is nebulous and vague, it's time to refactor.
Of course there are exceptions to every rule, and some classes with a lot of utility methods (like String) will be very large. But I generally take a hard look at the purpose of a class when it grows past about 300 lines. (For the second time - I do it the first time before the class grows past 0 lines.)
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My team has been tasked with creating what you can generically call an entity management application. The 3 primary entities being managed are: Merchants, Organizations, and Contacts
Separate pages have been created for the management of each entity. However, many of the functional patterns on these pages are quite similar. The 2 patterns in particular that are repeated everywhere I look are:
Pattern 1: Associating entity of type Y with entity of type X
Pattern 2: Listing entities of type Y that are already associated with entity of type X
Unfortunately these pages were created adhoc by multiple developers. This has resulted in a hodge-podge of solutions, none of which are readily reusable. So what I want to do is abstract out the two patterns I identified above into reusable components, but I am fairly new to wicket and I'm unsure of the best strategy to use.
My first thought is to encapsulate the patterns in two parameterized component classes that extend panel. But I would like to hear from those with more experience.
Any suggestions?
EDIT:
Forgot to mention, for any wondering, that any of the 3 entities can associate in a many to many relationship with either of the other 2.
Sounds like a pretty good idea to me. Additionally I'd check if any specific logic (like DAOs, Validators and stuff) could be provided via Dependency Injection (Google Guice comes to mind) so you could just use one panel with different handlers/workers/dataproviders for your different usecases.
It's hard to be more specific since your question is kind of broad and a little bit on tue vague side..