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People say Static utility methods are bad in OOP because they don't follow the OOP way of doing things.
I know static utility methods come from the more traditional procedural programming paradigm. And people say true OOP would be modelling the real world in objects sense encapsulating state & behaviour into one.
Is this true?
If so, is it best practice in modern OOP to not use static utility methods at all? Or is it still common to use them?
Would this latter question be more of a 'depends' situation?
Static methods (without side-effect) are in Computer Science named functions.
And I think it is general consensus that Functional Programming is superior.
Object Oriented Programming has the advantage that state is imminent to it, and in comparison to FP can make things more straight-forward.
However in the case of static methods functions are fine. Fine for low-level values. If the case is many functions operating on more complex classes, one may have an issue. Maybe those classes are unnecessarily complex, the logic too convoluted.
Compare BigDecimal with a theoretic version with static methods for add, multiply and so on. Functions would probably be better readable.
In short, yes, static utility methods are against the OOP paradigm. Should you use them? That depends on how much a purist you want to be, among some other things. Some people even call them evil :)
I think it's great that you are asking this question, though. The more you know about OOP, and the difference between it and the other paradims of software development, the better informed you are when choosing between alternatives.
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In Java, operators <, >, >= and <= are not defined for the primitive boolean type.
However, the corresponding wrapper class Boolean implements Comparable.
That is: true > false
is an error, but Boolean.TRUE.compareTo(Boolean.FALSE) > 0 is fine.
How come?
Did the language designers change their mind?
Why keep the incoherent behavior, then?
Although arbitrary, I can think of advantages to having a total order defined for booleans.
Are there any disadvantages?
Programming languages are not mathematical constructs. They are complex projects spanning many years and a lot of different people. As such, they are subjected to opinions, legacy, disagreements, hype cycles, influences of other languages, poor communication, and unfortunately sometimes also to mistakes and stupidity. You could argue that most decisions about a language are in fact arbitrary.
Your question is perfectly valid: why is it like this? Unfortunately without asking people who made the relevant commits how much they can still remember is not really a viable option. So your guess is as good as anybody else's.
It is what it is, but you are entitled to have your own opinion. Sadly, such inconsistencies can be in some cases frustrating to the point when people abandon a language and create a new one. But since computers are physical, limited things, any new language will also be imperfect and opinionated.
If you ask me, having a total ordering on boolean is a good idea - it wouldn't hurt anybody, while it could provide some limited benefit in certain (although very narrow) cases. But there are many more, much much bigger issues with Java. As it stands, I don't think Oracle will risk breaking any existing programs by changing this behaviour.
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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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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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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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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.)