Related
It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, visit the help center.
Closed 9 years ago.
Can someone please explain me what a software framework is? Why do we need a framework? What does a framework do to make programming easier?
I'm very late to answer it. But, I would like to share one example, which I only thought of today. If I told you to cut a piece of paper with dimensions 5m by 5m, then surely you would do that. But suppose I ask you to cut 1000 pieces of paper of the same dimensions. In this case, you won't do the measuring 1000 times; obviously, you would make a frame of 5m by 5m, and then with the help of it you would be able to cut 1000 pieces of paper in less time. So, what you did was make a framework which would do a specific type of task. Instead of performing the same type of task again and again for the same type of applications, you create a framework having all those facilities together in one nice packet, hence providing the abstraction for your application and more importantly many applications.
Technically, you don't need a framework. If you're making a really really simple site (think of the web back in 1992), you can just do it all with hard-coded HTML and some CSS.
And if you want to make a modern webapp, you don't actually need to use a framework for that, either.
You can instead choose to write all of the logic you need yourself, every time.
You can write your own data-persistence/storage layer, or - if you're too busy - just write custom SQL for every single database access.
You can write your own authentication and session handling layers.
And your own template rending logic.
And your own exception-handling logic.
And your own security functions.
And your own unit test framework to make sure it all works fine.
And your own... [goes on for quite a long time]
Then again, if you do use a framework, you'll be able to benefit from the good, usually peer-reviewed and very well tested work of dozens if not hundreds of other developers, who may well be better than you. You'll get to build what you want rapidly, without having to spend time building or worrying too much about the infrastructure items listed above.
You can get more done in less time, and know that the framework code you're using or extending is very likely to be done better than you doing it all yourself.
And the cost of this? Investing some time learning the framework. But - as virtually every web dev out there will attest - it's definitely worth the time spent learning to get massive (really, massive) benefits from using whatever framework you choose.
The summary at Wikipedia (Software Framework) (first google hit btw) explains it quite well:
A software framework, in computer programming, is an abstraction in which common code providing generic functionality can be selectively overridden or specialized by user code providing specific functionality. Frameworks are a special case of software libraries in that they are reusable abstractions of code wrapped in a well-defined Application programming interface (API), yet they contain some key distinguishing features that separate them from normal libraries.
Software frameworks have these distinguishing features that separate them from libraries or normal user applications:
inversion of control - In a framework, unlike in libraries or normal user applications, the overall program's flow of control is not dictated by the caller, but by the framework.[1]
default behavior - A framework has a default behavior. This default behavior must actually be some useful behavior and not a series of no-ops.
extensibility - A framework can be extended by the user usually by selective overriding or specialized by user code providing specific functionality.
non-modifiable framework code - The framework code, in general, is not allowed to be modified. Users can extend the framework, but not modify its code.
You may "need" it because it may provide you with a great shortcut when developing applications, since it contains lots of already written and tested functionality. The reason is quite similar to the reason we use software libraries.
A lot of good answers already, but let me see if I can give you another viewpoint.
Simplifying things by quite a bit, you can view a framework as an application that is complete except for the actual functionality. You plug in the functionality and PRESTO! you have an application.
Consider, say, a GUI framework. The framework contains everything you need to make an application. Indeed you can often trivially make a minimal application with very few lines of source that does absolutely nothing -- but it does give you window management, sub-window management, menus, button bars, etc. That's the framework side of things. By adding your application functionality and "plugging it in" to the right places in the framework you turn this empty app that does nothing more than window management, etc. into a real, full-blown application.
There are similar types of frameworks for web apps, for server-side apps, etc. In each case the framework provides the bulk of the tedious, repetitive code (hopefully) while you provide the actual problem domain functionality. (This is the ideal. In reality, of course, the success of the framework is highly variable.)
I stress again that this is the simplified view of what a framework is. I'm not using scary terms like "Inversion of Control" and the like although most frameworks have such scary concepts built-in. Since you're a beginner, I thought I'd spare you the jargon and go with an easy simile.
I'm not sure there's a clear-cut definition of "framework". Sometimes a large set of libraries is called a framework, but I think the typical use of the word is closer to the definition aioobe brought.
This very nice article sums up the difference between just a set of libraries and a framework:
A framework can be defined as a set of libraries that say “Don’t call us, we’ll call you.”
How does a framework help you? Because instead of writing something from scratch, you basically just extend a given, working application. You get a lot of productivity this way - sometimes the resulting application can be far more elaborate than you could have done on your own in the same time frame - but you usually trade in a lot of flexibility.
A simple explanation is: A framework is a scaffold that you can you build applications around.
A framework generally provides some base functionality which you can use and extend to make more complex applications from, there are frameworks for all sorts of things. Microsofts MVC framework is a good example of this. It provides everything you need to get off the ground building website using the MVC pattern, it handles web requests, routes and the like. All you have to do is implement "Controllers" and provide "Views" which are two constructs defined by the MVC framework. The MVC framework then handles calling your controllers and rendering your views.
Perhaps not the best wording but I hope it helps
at the lowest level, a framework is an environment, where you are given a set of tools to work with
this tools come in the form of libraries, configuration files, etc.
this so-called "environment" provides you with the basic setup (error reportings, log files, language settings, etc)...which can be modified,extended and built upon.
People actually do not need frameworks, it's just a matter of wanting to save time, and others just a matter of personal preferences.
People will justify that with a framework, you don't have to code from scratch. But those are just people confusing libraries with frameworks.
I'm not being biased here, I am actually using a framework right now.
In General, A frame Work is real or Conceptual structure of intended to serve as a support or Guide for the building some thing that expands the structure into something useful...
A framework provides functionalities/solution to the particular problem area.
Definition from wiki:
A software framework, in computer
programming, is an abstraction in
which common code providing generic
functionality can be selectively
overridden or specialized by user code
providing specific functionality.
Frameworks are a special case of
software libraries in that they are
reusable abstractions of code wrapped
in a well-defined Application
programming interface (API), yet they
contain some key distinguishing
features that separate them from
normal libraries.
A framework helps us about using the "already created", a metaphore can be like,
think that earth material is the programming language,
and for example "a camera" is the program, and you decided to create a notebook. You don't need to recreate the camera everytime, you just use the earth framework (for example to a technology store) take the camera and integrate it to your notebook.
A framework has some functions that you may need. you maybe need some sort of arrays that have inbuilt sorting mechanisms. Or maybe you need a window where you want to place some controls, all that you can find in a framework. it's a kind of WORK that spans a FRAME around your own work.
EDIT:
OK I m about to dig what you guys were trying to tell me ;) you perhaps havent noticed the information between the lines "WORK that spans a FRAME around ..."
before this is getting fallen deeper n deeper. I try to give a floor to it hoping you're gracfully:
a good explanation to the question "Difference between a Library and a Framework" I found here
http://ifacethoughts.net/2007/06/04/difference-between-a-library-and-a-framework/
Beyond definitions, which are sometimes understandable only if you already understand, an example helped me.
I think I got a glimmer of understanding when loooking at sorting a list in .Net; an example of a framework providing a functionality that's tailored by user code providing specific functionality. Take List.Sort(IComparer). The sort algorithm, which resides in the .Net framework in the Sort method, needs to do a series of compares; does object A come before or after object B? But Sort itself has no clue how to do the compare; only the type being sorted knows that. You couldn't write a comparison sort algorithm that can be reused by many users and anticipate all the various types you'd be called upon to sort. You've got to leave that bit of work up to the user itself. So here, sort, aka the framework, calls back to a method in the user code, the type being sorted so it can do the compare. (Or a delegate can be used; same point.)
Did I get this right?
I recently became part of a complex embedded project team for which I will be developing a part. For the part which is my responsibility there is only old code and not much documentation.
I am keen to make a good start but shyness and fear of appearing stupid makes it difficult to ask questions. How to ask questions ?
I wanted to ask what techniques do you guys use to understand a project ? I mean there are of lots of technical details which one must remember and keep in context in order to make a design. Your read the code and get some facts but how to move ahead ?
For instance you read the code and the document(s) and get some facts A and fact B . How to reach suitable conclusion X for which you may or may not have needed to take into account facts C and D also ?
Code-reading can be particularly difficult if there is not enough documentation and the code is poorly documented and badly written. I guess the best way now is to find the entry point of the code, and slowly understand its flows and what data it uses. I would keep a look out for
Structure - are there any partitioning of entities/system? Where in the code (and how) do they communicate with each other?
Data - what sort of structures are used to hold the global data? How are the data accessed and saved?
If you are doing C or C++, it is also important to find out how memory is handled and for C++ (and other related non-managed memory OOP languages, I guess), how are object ownership contained.
Since it is an embedded project, are there any non-standard code or coding constructs used?
Reading the code is balanced by writing the documentation.
Write the documentation that your replacement will need. Imagine someone who knows less than you. Explain it for that person.
When you cannot explain something to your replacement, ask questions.
When you have a complete description, you will "know" the system.
And you will have produced complete documentation.
You don't mention what kind of tests exist. If there are test cases, modify them and trace how this would affect the end result.
You might want to look at diagrams which give the entire picture of the logical structure of the system, like, for example, looking at class diagrams in an OOP system would be of great help. Looking at the design diagrams of large and complex apps gives you a clear understanding of how the internal modules of the system are organized and this way its makes the task of figuring out what functionality does a particular piece of code does much much easier. In the absence of diagrams, you're best bet would be to start from the entry point of the app, like main() and proceed from there while you draw(literally draw or write down on paper) your own conclusions about the system(this way you can have your own documentation) and ask your peers if they're correct.
My experience is that it's best to start with some kind of task -- a bug fix or other small change. That will provide focus to your learning. I find it hard to read through a binder or sift through pages of source code or documentation without having a way to apply it.
If you have a sandbox where you can play with changes that you've made without messing up the code base, that can be even more helpful.
These I come across this term a lot "crosscutting requirements/concerns" in programming world.
Although I think I have an idea what it means still I do not have a clear idea. I hear it a lot in web service and SOA in general.
Can this be explained using a hello world example?
It tends to mean "stuff that you want to do in lots of places, which doesn't have an awful lot to do with the real meat of that piece of code".
Common examples are:
Transaction handling
Security
Logging
Error handling
I find it's usually mentioned in respect to Aspect-Oriented Programming (AOP) which usually attempts to handle things like this declaratively, e.g. with attributes/annotations. As a gross simplification, it's a case of applying boiler-plate code (e.g. to verify the identity/authority of the user in the current context, or to log entry/exit of the method) automatically without making the code itself messy.
The standard "hello world" example for crosscutting is logging: You have an error in your production system and you have no clue what is going on. To solve it, you really need to see which functions in your code are called and what parameters they get and what they return.
This is a simple task that can be fully automated: Locate all functions (or a subset using a filter of some kind) and add a logging call to them which prints the name and the parameters. Since the code contains all the information you need to complete this task, what you really want is a tool that does it for you and which does it in a single place (instead of having you edit thousands of source files adding log statements everywhere).
I recommend you look at a framework like Postsharp and try out this example from the postsharp site. If you know java a lok into AspectJ is worth a look. But first you may want to read the link posted by Jon Skeet :)
I'm occasionally unfortunate enough to have to make alterations to very old, poorly not documented and poorly not designed code.
It often takes a long time to make a simple change because there is not much structure to the existing code and I really have to read a lot of code before I have a feel for where things would be.
What I think would help a lot in cases like this is a tool that would allow one to visualise an overview of the code, and then maybe even drill down for more detail. I suspect such a tool would be very hard to get right, given that is trying to find structure where there is little or none.
I guess this is not really a question, but rather a musing. I should make it into a question - What do others do to assist in getting their head around other peoples code, the good and the bad?
Hmm, this is a hard one, so much to say so little time ...
1) If you can run the code it makes life soooo much easier, breakpoints (especially conditional) break points are you friend.
2) A purists' approach would be to write a few unit tests, for known functionality, then refactor to improve code and understanding, then re-test. If things break, then create more unit tests - repeat until bored/old/moved to new project
3) ReSharper is good at showing where things are being used, what's calling a method for instance, it's static but a good start, and it helps with refactoring.
4) Many .net events are coded as public, and events can be a pain to debug at the best of times. Recode them to be private and use a property with add/remove. You can then use break point to see what is listening on an event.
BTW - I'm playing in the .Net space, and would love a tool to help do this kind of stuff, like Joel does anyone out there know of a good dynamic code reviewing tool?
I have been asked to take ownership of some NASTY code in the past - both work and "play".
Most of the amateurs I took over code for had just sort of evolved the code to do what they needed over several iterations. It was always a giant incestuous mess of library A calling B, calling back into A, calling C, calling B, etc. A lot of the time they'd use threads and not a critical section was to be seen.
I found the best/only way to get a handle on the code was start at the OS entry point [main()] and build my own call stack diagram showing the call tree. You don't really need to build a full tree at the outset. Just trace through the section(s) you're working on at each stage and you'll get a good enough handle on things to be able to run with it.
To top it all off, use the biggest slice of dead tree you can find and a pen. Laying it all out in front of you so you don't have to jump back and forward on screens or pages makes life so much simpler.
EDIT: There's a lot of talk about coding standards... they will just make poor code look consistent with good code (and usually be harder to spot). Coding standards don't always make maintaining code easier.
I do this on a regular basis. And have developed some tools and tricks.
Try to get a general overview (object diagram or other).
Document your findings.
Test your assumptions (especially for vague code).
The problem with this is that on most companies you are appreciated by result. That's why some programmers write poor code fast and move on to a different project. So you are left with the garbage, and your boss compares your sluggish progress with the quick and dirtu guy. (Luckily my current employer is different).
I generally use UML sequence diagrams of various key ways that the component is used. I don't know of any tools that can generate them automatically, but many UML tools such as BoUML and EA Sparx can create classes/operations from source code which saves some typing.
The definitive text on this situation is Michael Feathers' Working Effectively with Legacy Code. As S. Lott says get some unit tests in to establish behaviour of the lagacy code. Once you have those in you can begin to refactor. There seems to be a sample chapter available on the Object Mentor website.
I strongly recommend BOUML. It's a free UML modelling tool, which:
is extremely fast (fastest UML tool ever created, check out benchmarks),
has rock solid C++ import support,
has great SVG export support, which is important, because viewing large graphs in vector format, which scales fast in e.g. Firefox, is very convenient (you can quickly switch between "birds eye" view and class detail view),
is full featured, intensively developed (look at development history, it's hard to believe that so fast progress is possible).
So: import your code into BOUML and view it there, or export to SVG and view it in Firefox.
See Unit Testing Legacy ASP.NET Webforms Applications for advice on getting a grip on legacy apps via unit testing.
There are many similar questions and answers. Here's the search https://stackoverflow.com/search?q=unit+test+legacy
The point is that getting your head around legacy is probably easiest if you are writing unit tests for that legacy.
I haven't had great luck with tools to automate the review of poorly documented/executed code, cause a confusing/badly designed program generally translates to a less than useful model. It's not exciting or immediately rewarding, but I've had the best results with picking a spot and following the program execution line by line, documenting and adding comments as I go, and refactoring where applicable.
a good IDE (EMACS or Eclipse) could help in many cases. Also on a UNIX-platform, there are some tools for crossreferencing (etags, ctags) or checking (lint) or gcc with many many warning options turned on.
First, before trying to comprehend a function/method, i would refactor it a bit to fit your coding conventions (spaces, braces, indentation) and remove most of the comments if they seem to be wrong.
Then I would refactor and comment the parts you understood, and try to find/grep those parts over the whole source tree and refactor them there also.
Over the time, you get a nicer code, you like to work with.
I personally do a lot of drawing of diagrams, and figuring out the bones of the structure.
The fad de jour (and possibly quite rightly) has got me writing unit tests to test my assertions, and build up a safety net for changes I make to the system.
Once I get to a point where I'm comfortable enought knowing what the system does, I'll take a stab at fixing bugs in the sanest way possible, and hope my safety nets neared completion.
That's just me, however. ;)
i have actuaally been using the refactoring features of ReSharper to help m get a handle on a bunch of projects that i inherited recently. So, to figure out another programmer's very poorly structured, undocumented code, i actually start by refactoring it.
Cleaning up the code, renaming methods, classes and namespaces properly, extracting methods are all structural changes that can shed light on what a piece of code is supposed to do. It might sound counterintuitive to refactor code that you don't "know" but trut me, ReSharper really allows you to do this. Take for example the issue of red herring dead code. You see a method in a class or perhaps a strangely named variable. You can start by trying to lookup usages or, ungh, do a text search, but ReSharper will actually detect dead code and color it gray. As soon as you open a file you see in gray and with scroll bar flags what would have in the past been confusing red herrings.
There are dozens of other tricks and probably a number of other tools that can do similar things but i am a ReSharper junky.
Cheers.
Get to know the software intimately from a user's point of view. A lot can be learnt about the underlying structure by studying and interacting with the user interface(s).
Printouts
Whiteboards
Lots of notepaper
Lots of Starbucks
Being able to scribble all over the poor thing is the most useful method for me. Usually I turn up a lot of "huh, that's funny..." while trying to make basic code structure diagrams that turns out to be more useful than the diagrams themselves in the end. Automated tools are probably more helpful than I give them credit for, but the value of finding those funny bits exceeds the value of rapidly generated diagrams for me.
For diagrams, I look for mostly where the data is going. Where does it come in, where does it end up, and what does it go through on the way. Generally what happens to the data seems to give a good impression of the overall layout, and some bones to come back to if I'm rewriting.
When I'm working on legacy code, I don't attempt to understand the entire system. That would result in complexity overload and subsequent brain explosion.
Rather, I take one single feature of the system and try to understand completely how it works, from end to end. I will generally debug into the code, starting from the point in the UI code where I can find the specific functionality (since this is usually the only thing I'll be able to find at first). Then I will perform some action in the GUI, and drill down in the code all the way down into the database and then back up. This usually results in a complete understanding of at least one feature of the system, and sometimes gives insight into other parts of the system as well.
Once I understand what functions are being called and what stored procedures, tables, and views are involved, I then do a search through the code to find out what other parts of the application rely on these same functions/procs. This is how I find out if a change I'm going to make will break anything else in the system.
It can also sometimes be useful to attempt to make diagrams of the database and/or code structure, but sometimes it's just so bad or so insanely complex that it's better to ignore the system as a whole and just focus on the part that you need to change.
My big problem is that I (currently) have very large systems to understand in a fairly short space of time (I pity contract developers on this point) and don't have a lot of experience doing this (having previously been fortunate enough to be the one designing from the ground up.)
One method I use is to try to understand the meaning of the naming of variables, methods, classes, etc. This is useful because it (hopefully increasingly) embeds a high-level view of a train of thought from an atomic level.
I say this because typically developers will name their elements (with what they believe are) meaningfully and providing insight into their intended function. This is flawed, admittedly, if the developer has a defective understanding of their program, the terminology or (often the case, imho) is trying to sound clever. How many developers have seen keywords or class names and only then looked up the term in the dictionary, for the first time?
It's all about the standards and coding rules your company is using.
if everyone codes in different style, then it's hard to maintain other programmer code and etc, if you decide what standard you'll use have some rules, everything will be fine :) Note: that you don't have to make a lot of rules, because people should have possibility to code in style they like, otherwise you can be very surprised.
Is there a general procedure for programming extensibility capability into your code?
I am wondering what the general procedure is for adding extension-type capability to a system you are writing so that functionality can be extended through some kind of plugin API rather than having to modify the core code of a system.
Do such things tend to be dependent on the language the system was written in, or is there a general method for allowing for this?
I've used event-based APIs for plugins in the past. You can insert hooks for plugins by dispatching events and providing access to the application state.
For example, if you were writing a blogging application, you might want to raise an event just before a new post is saved to the database, and provide the post HTML to the plugin to alter as needed.
This is generally something that you'll have to expose yourself, so yes, it will be dependent on the language your system is written in (though often it's possible to write wrappers for other languages as well).
If, for example, you had a program written in C, for Windows, plugins would be written for your program as DLLs. At runtime, you would manually load these DLLs, and expose some interface to them. For example, the DLLs might expose a gimme_the_interface() function which could accept a structure filled with function pointers. These function pointers would allow the DLL to make calls, register callbacks, etc.
If you were in C++, you would use the DLL system, except you would probably pass an object pointer instead of a struct, and the object would implement an interface which provided functionality (accomplishing the same thing as the struct, but less ugly). For Java, you would load class files on-demand instead of DLLs, but the basic idea would be the same.
In all cases, you'll need to define a standard interface between your code and the plugins, so that you can initialize the plugins, and so the plugins can interact with you.
P.S. If you'd like to see a good example of a C++ plugin system, check out the foobar2000 SDK. I haven't used it in quite a while, but it used to be really well done. I assume it still is.
I'm tempted to point you to the Design Patterns book for this generic question :p
Seriously, I think the answer is no. You can't write extensible code by default, it will be both hard to write/extend and awfully inefficient (Mozilla started with the idea of being very extensible, used XPCOM everywhere, and now they realized it was a mistake and started to remove it where it doesn't make sense).
what makes sense to do is to identify the pieces of your system that can be meaningfully extended and support a proper API for these cases (e.g. language support plug-ins in an editor). You'd use the relevant patterns, but the specific implementation depends on your platform/language choice.
IMO, it also helps to use a dynamic language - makes it possible to tweak the core code at run time (when absolutely necessary). I appreciated that Mozilla's extensibility works that way when writing Firefox extensions.
I think there are two aspects to your question:
The design of the system to be extendable (the design patterns, inversion of control and other architectural aspects) (http://www.martinfowler.com/articles/injection.html). And, at least to me, yes these patterns/techniques are platform/language independent and can be seen as a "general procedure".
Now, their implementation is language and platform dependend (for example in C/C++ you have the dynamic library stuff, etc.)
Several 'frameworks' have been developed to give you a programming environment that provides you pluggability/extensibility but as some other people mention, don't get too crazy making everything pluggable.
In the Java world a good specification to look is OSGi (http://en.wikipedia.org/wiki/OSGi) with several implementations the best one IMHO being Equinox (http://www.eclipse.org/equinox/)
Find out what minimum requrements you want to put on a plugin writer. Then make one or more Interfaces that the writer must implement for your code to know when and where to execute the code.
Make an API the writer can use to access some of the functionality in your code.
You could also make a base class the writer must inherit. This will make wiring up the API easier. Then use some kind of reflection to scan a directory, and load the classes you find that matches your requirements.
Some people also make a scripting language for their system, or implements an interpreter for a subset of an existing language. This is also a possible route to go.
Bottom line is: When you get the code to load, only your imagination should be able to stop you.
Good luck.
If you are using a compiled language such as C or C++, it may be a good idea to look at plugin support via scripting languages. Both Python and Lua are excellent languages that are used to script a large number of applications (Civ4 and blender use Python, Supreme Commander uses Lua, etc).
If you are using C++, check out the boost python library. Otherwise, python ships with headers that can be used in C, and does a fairly good job documenting the C/python API. The documentation seemed less complete for Lua, but I may not have been looking hard enough. Either way, you can offer a fairly solid scripting platform without a terrible amount of work. It still isn't trivial, but it provides you with a very good base to work from.