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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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Currently my program is filled with many ugly references that often make field or method access look like this: weakReference1.get().weakReference2.get().field1.getSomeCustomObject().field2. I want to move to shorter and faster strong references like field1.field2. But my program design is such that I will also have to go for an ArrayList element-by-element search (in a for-loop) instead of accessing a WeakHashMap by get() method.
Thus, I'd like to understand, can moving to simpler references compensate for rejecting HashMap performance wise. Herewith I presume that WeakHashMap.get() is much faster than a loop-search of ArrayList.
Can someone, please, give me a rough estimate? Or maybe there's even an appropriate comparison table like this one. I'd appreciate that.
Thank you.
Currently my program is filled with many ugly references that often make field or method access look like this:
weakReference1.get().weakReference2.get().field1.getSomeCustomObject().field2
Given that the objects involved are not Data Transfer Objects
this is a violation of the law of Demeter aka Don't talk to Strangers / Tell, don't ask!
Following this LoD principle you should move the operations working with the data in field2 to a new method in the class SomeCustomObject.
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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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I am currently working on an uni assignment. We have to write Javadoc comments. My problem is that I don't really know to whom I'm "talking" here.
Some examples for comments to different methods in my project:
"The next thing we care about is the number of..."
"We want to remove those items from the list because..."
So the questions is: can i put Javadocs like that or do I have to write them in formal language? And who do I adress in my sentences (if I can adress someone).
It's entirely up to you / your team how formal or informal to make your Javadoc.
It's relatively rare to directly address anyone (either with "you" or "we"), but again, it's your call. Consider the JDK's docs, which typically go something like this:
The String class represents character strings. All string literals in Java programs, such as "abc", are implemented as instances of this class.
Direct, clear, and impersonal. Just state the facts.
Another example (from Object#equals):
Note that it is generally necessary to override the hashCode method whenever this method is overridden, so as to maintain the general contract for the hashCode method, which states that equal objects must have equal hash codes.
Notice how it didn't say "Note that you must generally override..." It doesn't tell anyone what to do, just notes that if doing X, generally it's necessary to do Y.
Javadocs matter most if you're publishing to third parties. You won't be present to expound on your code. Third parties will want to just use your classes wo/ worrying about how they fulfill their contract. Your documentation should tell them what they need to know: what the terms of the contract is. They need to know what to provide, what to expect back, exceptions, invariants, etc.
I would say keep the language formal in that case. It reflects better on you.
You don't communicate with third parties the same way you do your friends. Better to keep it formal.
I would stop using "we" and think more in terms of "you". It's about the consumer of your library, not the developers.
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i have been reading about this topic , and the more i read the more confused i get ,
can somebody please elaborate , we were using language C which follows structural approach ,
so what was wrong with this approach , that we moved to create a object oriented language JAVA .
I have been reading so many theoretical aspects , can some body please give more of a few practical illustrations ,
WHY WE NEEDED OBJECT ORIENTED APPROACH IN THE FIRST PLACE
I am not looking for an answer to be given in any interview or tutorial
I am looking for an answer to get the better understanding/practical importance of object oriented aproach
There are many explanations regarding this. But I would like to refer this
Modularity: The source code for a class can be written and maintained independently of the source code for other classes. Once
created, an object can be easily passed around inside the system.
Information-hiding: By interacting only with an object's methods, the details of its internal implementation remain hidden from
the outside world.
Code re-use: If a class already exists, you can use objects from that class in your program. This allows programmers to
implement/test/debug complex, task-specific objects, which you can
then use in your own code.
Easy Debugging: If a particular object turns out to be a problem, you can simply remove it from your application and plug in a
different object as its replacement. This is analogous to fixing
mechanical problems in the real world. If a bolt breaks, you replace
it, not the entire machine.