Definitely not looking for anyone to do my homework, just having a little trouble understanding naming conventions in Eclipse as well as bracket placement.
I'm still getting pretty tripped up by not knowing exactly what to name my (not sure what the correct word is here) main class, the class I originally create in Eclipse after I create a Java Project and create a Package inside of my Java Project and then right-click my Package and select New/Class. Here is a link to the code and instructions the professor gave me by the way.
Right now I'm calling my "main class" Container in my Java Project/Package. I named it that because it was the first class declared in the code I have. Is this a bad idea, should I name it something else?
Also, is there anyone that can help me understand bracket placement a little better? I understand that brackets section off sections of code and that you can layer and nest sections of code within other code using brackets. What I don't get (for this current assignment especially) is how should I be nesting code inside other code using the brackets.
For instance, in the link I provided above my professor has structured the brackets so that the abstract class 'Container', as well as all the classes that extend 'Container' are completely cut-off and independent from each other as well as the rest of the code. The only part of the code which shares brackets with another is the class 'ContainerCollection' which nests the Main Method inside of it.
On all of my other assignments my code was structured so that I had a class declared at the top of my program which contained in its brackets all of the other classes, constructor, and methods including my Main Method. Here's an example
of what I'm used to seeing, structurally speaking.
Anyway, I feel like I'm missing something fundamental about how these brackets section off and nest code. For instance, I didn't think that you could have sections independent of all other sections in the code, I thought everything had to be within the brackets of the main class. I would really appreciate any insight into this at all.
Hi hi and welcome to programming :) It seems to me you have some problems understanding some fundamental stuff in coding itself. I'll try and answer some of the questions that you have outlined here (without getting too deep into the technicalities) as well as give an overview of some of the code that you've linked.
1) Naming your "Main" class.
The name of your 'main' class doesn't need to be anything special. Usually the class that holds the critical "main" method (that is, the public static void main(String[] args) { ... }) is just the class that "runs" your program. When I was doing assignments I often just named it CalculatorRunner.java or GameRunner.java or whatever.
2) Constructors, Classes, Methods, Brackets
From what I see in your questions, it seems like you also have a little trouble discerning the difference between Classes, Constructors, Methods. Do a little research and you'll learn to spot the subtle difference between the syntax and bracketing. :)
The code that your professor linked
The code that your professor linked is set out somewhat poorly. Several classes are defined in the single text file which can be confusing for a new programmer. "OMG WHY ARE THERE SO MANY CLASSES IN HERE?! WHAT'S GOING ON?!" LOL don't panic. It's probably because your professor's lazy and doesn't want to separate the classes out. It's acceptable to the Java VM but not so fun for a programmer. Spot where the classes are and put them into their own class files and things will be much clearer. The Fantasy football code is much clearer and doesn't have multiple classes embedded in one.
Anyways, the questions you've asked is pretty textbook... practice a bit more and it'll all slowly come together. Hope it helps.
Related
So - I am really really digging coffeescript. But, I am curious how the possibility of repetition of code is dealth with across a large repository of code.
For instance.
Lets say I create a simple class.
class Cart
constructor: (#session, #group) ->
class Shoes extends Cart
compiler will create __extends and __hasProp methods.
Mind you, this is just one example -- pretty much this happens with loops etc... So, granted each bit of code is usually in its walled garden.. BUT, there could be many many of the same methods thru-out a code base.... because of the compiler just creating generic helper methods that are all the same.
Anyone else have to contend with this or deal with that possible bloat?
That is probably a lot more specific to what build tool you are using to manage a large codebase. grunt-contrib-coffee for example provides the ability to concatenate before compilation which means something like the __extends method should only get declared once. Likewise, I believe, asset pipeline in rails makes similar optimizations through the require statements.
We seems to be abstracting a lot of logic way from web pages and creating "helper" classes. Sadly, these classes are all sounding the same, e.g
ADHelper, (Active Directory)
AuthenicationHelper,
SharePointHelper
Do other people have a large number of classes with this naming convention?
I would say that it qualifies as a code smell, but remember that a code smell doesn't necessarily spell trouble. It is something you should look into and then decide if it is okay.
Having said that I personally find that a name like that adds very little value and because it is so generic the type may easily become a bucket of non-related utility methods. I.e. a helper class may turn into a Large Class, which is one of the common code smells.
If possible I suggest finding a type name that more closely describes what the methods do. Of course this may prompt additional helper classes, but as long as their names are helpful I don't mind the numbers.
Some time ago I came across a class called XmlHelper during a code review. It had a number of methods that obviously all had to do with Xml. However, it wasn't clear from the type name what the methods had in common (aside from being Xml-related). It turned out that some of the methods were formatting Xml and others were parsing Xml. So IMO the class should have been split in two or more parts with more specific names.
As always, it depends on the context.
When you work with your own API I would definitely consider it a code smell, because FooHelper indicates that it operates on Foo, but the behavior would most likely belong directly on the Foo class.
However, when you work with existing APIs (such as types in the BCL), you can't change the implementation, so extension methods become one of the ways to address shortcomings in the original API. You could choose to names such classes FooHelper just as well as FooExtension. It's equally smelly (or not).
Depends on the actual content of the classes.
If a huge amount of actual business logic/business rules are in the helper classes, then I would say yes.
If the classes are really just helpers that can be used in other enterprise applications (re-use in the absolute sense of the word -- not copy then customize), then I would say the helpers aren't a code smell.
It is an interesting point, if a word becomes 'boilerplate' in names then its probably a bit whiffy - if not quite a real smell. Perhaps using a 'Helper' folder and then allowing it to appear in the namespace keeps its use without overusing the word?
Application.Helper.SharePoint
Application.Helper.Authentication
and so on
In many cases, I use classes ending with Helper for static classes containing extension methods. Doesn't seem smelly to me. You can't put them into a non-static class, and the class itself does not matter, so Helper is fine, I think. Users of such a class won't see the class name anyway.
The .NET Framework does this as well (for example in the LogicalTreeHelper class from WPF, which just has a few static (non-extension) methods).
Ask yourself if the code would be better if the code in your helper class would be refactored to "real" classes, i.e. objects that fit into your class hierarchy. Code has to be somewhere, and if you can't make out a class/object where it really belongs to, like simple helper functions (hence "Helper"), you should be fine.
I wouldn't say that it is a code smell. In ASP.NET MVC it is quite common.
Maybe its because I've been coding around two semesters now, but the major stumbling block that I'm having at this point is converting the professor's project description and requirements to actual code. Since I'm currently in Algorithms 101, I basically do a bottom-up process, starting with a blank whiteboard and draw out the object and method interactions, then translate that into classes and code.
But now the prof has tossed interfaces and abstract classes into the mix. Intellectually, I can recognize how they work, but am stubbing my toes figuring out how to use these new tools with the current project (simulating a web server).
In my professors own words, mapping the abstract description to Java code is the real trick. So what steps are best used to go from English (or whatever your language is) to computer code? How do you decide where and when to create an interface, or use an abstract class?
So what steps are best used to go from English (or whatever your language is) to computer code?
Experience is what teaches you how to do this. If it's not coming naturally yet (and don't feel bad if it doesn't, because it takes a long time!), there are some questions you can ask yourself:
What are the main concepts of the system? How are they related to each other? If I was describing this to someone else, what words and phrases would I use? These thoughts will help you decide what classes are useful to think about.
What sorts of behaviors do these things have? Are there natural dependencies between them? (For example, a LineItem isn't relevant or meaningful without the context of an Order, nor is an Engine much use without a Car.) How do the behaviors affect the state of the other objects? Do they communicate with each other, and if so, in what way? These thoughts will help you develop the public interfaces of your classes.
That's just the tip of the iceberg, of course. For more about this thought process in general, see Eric Evans's excellent book, Domain-Driven Design.
How do you decide where and when to create an interface, or use an abstract class?
There's no hard and fast prescriptions; again, experience is the best guide here. That said, there's certainly some rules of thumb you can follow:
If several unrelated or significantly different object types all provide the same kind of functionality, use an interface. For example, if the Steerable interface has a Steer(Vector bearing) method, there may be lots of different things that can be steered: Boats, Airplanes, CargoShips, Cars, et cetera. These are completely unrelated things. But they all share the common interface of being able to be steered.
In general, try to favor an interface instead of an abstract base class. This way you can define a single implementation which implements N interfaces. In the case of Java, you can only have one abstract base class, so you're locked into a particular inheritance hierarchy once you say that a class inherits from another one.
Whenever you don't need implementation from a base class, definitely favor an interface over an abstract base class. This would also be handy if you're operating in a language where inheritance doesn't apply. For example, in C#, you can't have a struct inherit from a base class.
In general...
Read a lot of other people's code. Open source projects are great for that. Respect their licenses though.
You'll never get it perfect. It's an iterative process. Don't be discouraged if you don't get it right.
Practice. Practice. Practice.
Research often. Keep tackling more and more challenging projects / designs. Even if there are easy ones around.
There is no magic bullet, or algorithm for good design.
Nowadays I jump in with a design I believe is decent and work from that.
When the time is right I'll implement understanding the result will have to refactored ( rewritten ) sooner rather than later.
Give this project your best shot, keep an eye out for your mistakes and how things should've been done after you get back your results.
Keep doing this, and you'll be fine.
What you should really do is code from the top-down, not from the bottom-up. Write your main function as clearly and concisely as you can using APIs that you have not yet created as if they already existed. Then, you can implement those APIs in similar fashion, until you have functions that are only a few lines long. If you code from the bottom-up, you will likely create a whole lot of stuff that you don't actually need.
In terms of when to create an interface... pretty much everything should be an interface. When you use APIs that don't yet exist, assume that every concrete class is an implementation of some interface, and use a declared type that is indicative of that interface. Your inheritance should be done solely with interfaces. Only create concrete classes at the very bottom when you are providing an implementation. I would suggest avoiding abstract classes and just using delegation, although abstract classes are also reasonable when two different implementations differ only slightly and have several functions that have a common implementation. For example, if your interface allows one to iterate over elements and also provides a sum function, the sum function is a trivial to implement in terms of the iteration function, so that would be a reasonable use of an abstract class. An alternative would be to use the decorator pattern in that case.
You might also find the Google Techtalk "How to Design a Good API and Why it Matters" to be helpful in this regard. You might also be interested in reading some of my own software design observations.
Also, for the coming future, you can keep in pipeline to read the basics on domain driven design to align yourself to the real world scenarios - it gives a solid foundation for requirements mapping to the real classes.
Currently I am making some decisions for my first objective-c API. Nothing big, just a little help for myself to get things done faster in the future.
After reading a few hours about different patterns like making categories, singletons, and so on, I came accross something that I like because it seems easy to maintain for me. I'm making a set of useful functions, that can be useful everywhere.
So what I did is:
1) I created two new files (.h, .m), and gave the "class" a name: SLUtilsMath, SLUtilsGraphics, SLUtilsSound, and so on. I think of that as kind of "namespace", so all those things will always be called SLUtils******. I added all of them into a Group SL, which contains a subgroup SLUtils.
2) Then I just put my functions signatures in the .h file, and the implementations of the functions in the .m file. And guess what: It works!! I'm happy with it, and it's easy to use. The only nasty thing about it is, that I have to include the appropriate header every time I need it. But that's okay, since that's normal. I could include it in the header prefix pch file, though.
But then, I went to toilet and a ghost came out there, saying: "Hey! Isn't it better to make real methods, instead of functions? Shouldn't you make class methods, so that you have to call a method rather than a function? Isn't that much cooler and doesn't it have a better performance?" Well, for readability I prefer the functions. On the other hand they don't have this kind of "named parameters" like methods, a.f.a.i.k..
So what would you prefer in that case?
Of course I dont want to allocate an object before using a useful method or function. That would be harrying.
Maybe the toilet ghost was right. There IS a cooler way. Well, for me, personally, this is great:
MYNAMESPACECoolMath.h
#import <Foundation/Foundation.h>
#interface MYNAMESPACECoolMath : NSObject {
}
+ (float)randomizeValue:(float)value byPercent:(float)percent;
+ (float)calculateHorizontalGravity:(CGPoint)p1 andPoint:(CGPoint)p2;
// and some more
#end
Then in code, I would just import that MYNAMESPACECoolMath.h and just call:
CGFloat myValue = [MYNAMESPACECoolMath randomizeValue:10.0f byPercent:5.0f];
with no nasty instantiation, initialization, allocation, what ever. For me that pattern looks like a static method in java, which is pretty nice and easy to use.
The advantage over a function, is, as far as I noticed, the better readability in code. When looking at a CGRectMake(10.0f, 42.5f, 44.2f, 99.11f) you'll may have to look up what those parameters stand for, if you're not so familiar with it. But when you have a method call with "named" parameters, then you see immediately what the parameter is.
I think I missed the point what makes a big difference to a singleton class when it comes to simple useful methods / functions that can be needed everywhere. Making special kind of random values don't belong to anything, it's global. Like grass. Like trees. Like air. Everyone needs it.
Performance-wise, a static method in a static class compile to almost the same thing as a function.
Any real performance hits you'd incur would be in object instantiation, which you said you'd want to avoid, so that should not be an issue.
As far as preference or readability, there is a trend to use static methods more than necessary because people are viewing Obj-C is an "OO-only" language, like Java or C#. In that paradigm, (almost) everything must belong to a class, so class methods are the norm. In fact, they may even call them functions. The two terms are interchangeable there. However, this is purely convention. Convention may even be too strong of a word. There is absolutely nothing wrong with using functions in their place and it is probably more appropriate if there are no class members (even static ones) that are needed to assist in the processing of those methods/functions.
The problem with your approach is the "util" nature of it. Almost anything with the word "util" it in suggests that you have created a dumping ground for things you don't know where to fit into your object model. That probably means that your object model is not in alignment with your problem space.
Rather than working out how to package up utility functions, you should be thinking about what model objects these functions should be acting upon and then put them on those classes (creating the classes if needed).
To Josh's point, while there is nothing wrong with functions in ObjC, it is a very strongly object-oriented language, based directly on the grand-daddy of object-oriented languages, Smalltalk. You should not abandon the OOP patterns lightly; they are the heart of Cocoa.
I create private helper functions all the time, and I create public convenience functions for some objects (NSLocalizedString() is a good example of this). But if you're creating public utility functions that aren't front-ends to methods, you should be rethinking your patterns. And the first warning sign is the desire to put the word "util" in a file name.
EDIT
Based on the particular methods you added to your question, what you should be looking at are Categories. For instance, +randomizeValue:byPercent: is a perfectly good NSNumber category:
// NSNumber+SLExtensions.h
- (double)randomizeByPercent:(CGFloat)percent;
+ (double)randomDoubleNear:(CGFloat)percent byPercent:(double)number;
+ (NSNumber *)randomNumberNear:(CGFloat)percent byPercent:(double)number;
// Some other file that wants to use this
#import "NSNumber+SLExtensions.h"
randomDouble = [aNumber randomizeByPercent:5.0];
randomDouble = [NSNumber randomDoubleNear:5.0 byPercent:7.0];
If you get a lot of these, then you may want to split them up into categories like NSNumber+Random. Doing it with Categories makes it transparently part of the existing object model, though, rather than creating classes whose only purpose is to work on other objects.
You can use a singleton instance instead if you want to avoid instantiating a bunch of utility objects.
There's nothing wrong with using plain C functions, though. Just know that you won't be able to pass them around using #selector for things like performSelectorOnMainThread.
When it comes to performance of methods vs. functions, Mike Ash has some great numbers in his post "Performance Comparisons of Common Operations". Objective-C message send operations are extremely fast, so much so that you'd have to have a really tight computational loop to even see the difference. I think that using functions vs. methods in your approach will come down to the stylistic design issues that others have described.
Optimise the system, not the function calls.
Implement what is easiest to understand and then when the whole system works, profile it and speed up what's slow. I doubt very much that the objective-c runtime overhead of a static class is going to matter one bit to your whole app.
I'm find I have several places that having public static inner classes designed that extend "helper" classes makes my code a lot more type safe and, in my opinion, readable. For example, imagine I have a "SearchCriteria" class. There are a lot of commonalities for the different things I search for (a search term and then a group of search term types, a date range, etc.) By extending it in a static inner class, I tightly couple the extension and the searchable class with the specific differences. This seems like a bad idea in theory (Tight Coupling Bad!) but the extension is specific to this searchable class (One Class, One Purpose).
My question is, in your experience, has the use of static inner classes (or whatever your language equivelent is) made your code more readable/maintainable or has this ended up biting you in the EOF?
Also, I'm not sure if this is community wiki material or not.
Sounds perfectly reasonable to me. By making it an inner class, you're making it easy to find and an obvious candidate for review when the searchable class changes.
Tight coupling is only bad when you couple things that don't really belong together just because one of them happens to call the other one. For classes that collaborate closely, e.g. when, as in your case, one of them exists to support the other, then it's called "cohesion", and it's a good thing.
Note that the class is not the unit of reuse. Therefore, some coupling between classes is normal and expected. The unit of reuse is usually a collection of related classes.
In Python, we have a variety of structures.
Packages. They contain modules. These are essentially directories with a little bit of Python machinery thrown in.
Modules. They contain classes (and functions). These are files; and can contain any number of closely-related classes. Often, the "inner class" business is handled at this level.
Classes. These can contain inner class definitions as well as method functions. Sometimes (not very often) inner classes may actually be used. This is rare, since the module-level coupling among classes is usually perfectly clear.
The only caveat with using inner classes is making sure you're not repeating yourself all over the place - as in - make sure, when you define an inner class, you're not going to need to use that functionality anywhere else, and, that that functionality is necessarily coupled with the outer class. You don't want to end up with a whole bunch of inner classes that all implement the exact same setOrderyByNameDesc() method.
The point in "loose coupling" is to keep the two classes separate so that if there are code changes in your "SearchCriteria" class nothing would have to be change in the other classes. I think that the static inner classes you are talking about could potentially make maintaining code a nightmare. One change in SearchCriteria could send you searching through all of the static classes to figure out which ones are now broken because of the update. Personally, I would stay away from any such inner classes unless it is really needed for some reason.