Related
Where can I find a tutorial for writing DownThemAll AntiContainer plugins in JSON?
The documentation is confusing...
Considering the fact that, five hours after you asked it, this question is already one of the top ten Google results for "DownThemAll AntiContainer tutorial", it seems unlikely that any more detailed tutorials exist.
Perhaps you can learn more by examining the source code of existing plugins or by contacting one of the plugin authors, nmaier and poke? (You need a GitHub account to use the "message" feature.)
In case anyone is still looking:
This is a nice Wiki-Tutotrial about it https://github.com/downthemall/anticontainer/wiki/Writing-plugins
however, it does not explain the fine details, to grasp how this can be applied to a specific problem
As it currently stands, this question is not a good fit for our Q&A format. We expect answers to be supported by facts, references, or expertise, but this question will likely solicit debate, arguments, polling, or extended discussion. If you feel that this question can be improved and possibly reopened, visit the help center for guidance.
Closed 9 years ago.
Currently I have started on very large Legacy Project and am in a situation which I always feared Reading and Understanding Other People's code, I have known that this is an essential skill which is required but haven't developed it as till date it was not required and now its like necessity to develop this skill rather than hobby and so I would like to know from SO Readers about:
How you have overcome the hurdle of reading other people's code ?
What techniques or skill have you developed to polish your art of reading and understanding other people code ?
Are there any books or articles which you have referred to or in general how did you developed the skill of reading and understanding other people's code ?
I would highly appreciate useful answers to this questions as now I can understand how one would feel while trying to understand my code.
Practice. Practice. Practice.
I overcame the hurdle by interacting with people on open-source projects. Discussing my contributions with others, and seeing their suggestions and ways of looking at things really opened my eyes.
I suggest you find a project that fits you, check out the source and contribute what you can (no matter how small to begin with). Over time the skill of reading code should just come naturally. Some projects even offer mentors specifically for helping out new contributors.
Michael Feathers' Working Effectively with Legacy Code is a great resource that contains a large number of techniques for working with older code.
Practice, Practice, Practice.
If you can, talk to whoever wrote the code or has an idea about it. Draw lots of pictures and have them explain big things to you while YOU write comments.
The quickest way to find your way around is to get lost. Dive into the code and break stuff. See if you can change an int into to a string or something.
Patience: Understand that reading code is more difficult than writing new code. Then you need to respect the code, even if it is not very readable, for it does its job and in many cases pretty efficiently. You need to give the code time and effort to understand it.
Understand the Architecture: It is best if there is any documentation on this. Try talking to people who know more about it if they are available.
Test it: You need to spend some time testing and debugging the code so you know what it does.
For those parts you understand, write some unit tests if possible so you can use them later.
Be Unassuming: Many times the names of the patterns are misused. The classes have names which do not indicate their purpose. So don't assume anything about them.
Learn Refactoring: The best book I found on this topic is Refactoring: Improving the Design of Existing Code - By Martin Fowler. Working Effectively with Legacy Code is another awesome one.
I don't know of any way to do it, i have participated in several proyects, where i have to undertand by my own, how do they think in and achieve that solution, so i can undertand it too.
That's why every time i can, i recommend, if you are a developer, try comment the code, all you can, because, you don't know if someone will find it useful (i think i make my point)
If you're not a developer, you should find someone to support you.
How do you learn to read what other people have written? You get really good at writing yourself and try to make sure the person is as good a writer as possible (suggest things they could do better, like adding some darn comments) Sadly, code is almost always read by someone else other than the author. Practice, and familiarity with some of the person's other code can help. But whenever you spend over 5 minutes figuring out what a particular line means, note how they could have done it better, and make sure you never make the same mistake.
good luck. :D
When I'm approaching an unfamiliar code base, I like to start at the beginning. Find main(), and write out a summary of what main() does. Create a list of the functions/methods called in main(). If you're visual, create a flowchart of main().
Once you have a list of the methods called directly from main(), look up those methods and repeat the process. As you figure out what each of those methods is doing, write it up in JavaDoc format and paste it into its corresponding box in the flowchart. If it's an API call, document which API it is using and put a link to the relevant API documentation.
Working recursively, you will create a map of the application and figure out what the program actually does. Once you know what it actually does, you will be able to find inconsistencies between what it does and what it's supposed to do.
The answer varies depending on the tools and documentation available.
If any documentation is available, I try to understand the high level overview of the system - the different modules, interfaces and subsystem interaction. This helps to divide and conquer the code into sizable pieces as you go along reading the code. If any design patterns are commonly used across the code try to build up your knowledge on that.
Also depending on the tools available I may use any of the popular source code browsers (Source Navigator/Source Insight) to quickly view the dependencies (class hierarchy etc). This speeds up code understanding. Also if I have some handy unit testing framework try playing with the code- different inputs and expected output. I also recommend using debugger to step through selected complex functions to get a hang of the code flow.
Here's a somewhat general computer question. I've always been able to follow the LOGIC of programming, but when I go to code something, I always find that I don't know some method or another to get what I need to get done. When I see it, I always think, "OF COURSE!".
How do you go about finding relevant methods for your programming needs that are "built-in?" I don't enjoy re-inventing the wheel, but I find it difficult to find what I need to do what I want to do.
First try Google:
You can use google to search your required method. For example If I want to search a value in array in PHP then I go to Google and type "Search values in array in PHP". I find my required function at first place.
Then try Standard Documentation:
Try standard documentation to search for your required method. For example if my problem is related to strings in PHP then I go to String Functions documentation and find the required function.
Finally try Stackoverflow:
Otherwise you can ask your problem at Stackoverflow for your required methods and libraries. You will always get a shortest way.
What you are asking here is for the best way to do research. Well, that's hard skill to explain, even more so to teach.
Nevertheless here are some tips:
Go to a search engine. It makes no
sense to start in a place like MSDN,
since all of its content is indexed
by the search engines anyway.
Phrase your question several
different ways.
As you learn more
about the issue you will learn new
vocabulary about it. Use that new
vocabulary to do even more searches.
If the searches turn out empty,
switch to browsing a specific
section of the official
documentation that you think is the
most related to what you are doing. If nothing else, it will expand your horizons around the issue and give you more vocabulary to do more searches.
Finally, if all else fails ask a question on StackOverflow explaining what you want to do as clearly as possible.
Note that if there's a simple API that does what you need, you will rarely reach step 4.
You say:
It's very frustrating to suddenly find
an "easy" button mid-way through.
Try to see it differently. Think of these moments as blessings. You've just learned something. You invested a lot of effort - and instead of seeing that effort as wasted, see it as critical to proper learning. You - better than the guy who just happened across the magic method - really understand what it's for and something about how it works. And you really, really, understand why you need it, and you properly appreciate its value. You're never going to forget that method.
So it was costly, but you learned something important. Celebrate, and move on.
It is usually included in some form of documentation. Most IDEs support the documentation format and gives you auto-complete functionality.
if you are using MVS so MSDN is really good for it
In addition to this and this answer above, google's basic and advanced searching tips prove very helpful.
In addition to above, changing the order of keywords in search criteria also sorts the list in different orders.
In essence I believe that searching is still an art rather than a science, and is best learnt - quoting from David Reis' answer above: "2. As you learn more about the issue you will learn new vocabulary about it. Use that new vocabulary to do even more searches."
Search in the API documentation. But the best way to (I found so) is to search on the internet for multiple solutions and then choose the one that you think is best. Make your search as narrow as possible. For example you want to implement random number generation function, then search like this, "How to generate random numbers in Java?".
Namespaces, namingconventions, Autocomplete/Intellisence
I assume that you are trying to find some kind of Object-Oriented-apis . I use .net in my example.
First try to find a class that might be responsable for the method you are looking for.
Example: If you want to "Make a new Directory in the Filesystem" you must know (or learn) that (in dotnet) these classes are in the namespace System.IO:
This namespace contains subnamespaces like Compresseion and Classes like File, Path, Directory, ...
Second you sould know NamingConventions. There are common Naming-Prefixes for methods like Get, Set, Insert, Create. In the documentation for class Directory you will find a CreateDirectory-Method.
If you have an intelligent editor that knows your programming language and the classes and namespaces learning is much easier. In the dotnet-world this feature is called Autocomplete/Intellisence
As a student in computer engineering I have been pressured to type up very detailed comments for everything I do. I can see this being very useful for group projects or in the work place but when you work on your own projects do you spend as much time commenting?
As a personal project I am working on grows more and more complicated I sometimes feel as though I should be commenting more but I also feel as though it's a waste of time since I will probably be the only one working on it. Is it worth the time and cluttered code?
Thoughts?
EDIT: This has given me a lot to think about. Thanks for all your input! I never expected this large of a response.
Well considered comments illuminate when the code cannot. Well considered function and variable names eliminate the need for copious comments. If you find it necessary to comment everything, consider simplifying your code.
If you ever look at code you wrote 6 months before, you will be wondering why you did not comment better.
If the code is well written, with short methods (see Composed Method pattern) and meaningful names, then the code needs very little comments. Only comments which explain the "why" are useful - the comments explaining "what" should be replaced by improving the code so much that it's obvious what it does. Comments should not be used as an excuse for writing bad code.
Public APIs, especially in closed-source apps, are perhaps the only place where thorough javadocs are recommended - and then you need to take the effort to maintain them and keep them always accurate and up-to-date. A misleading or outdated comment is worse than no comment. It's better to document what the code does by writing tests for it and using good names for the tests.
The book Clean Code has a good chapter about comments.
Unit tests and the like are the best forms of code documentation. Some testing frameworks write out a spec of what the class under test should do, giving people a great introduction to how a piece of code works in pure english while also providing very clean way to implement the tests itself.
Examples of that are Scala's ScalaTest or RSpec for Ruby.
I find that unless some weird hacky thing is required by the code in question, it is usually not beneficial to comment it. Also, it adds a lot of overhead because you have to maintain the comments... and maintaining the code and tests is already enough work.
Remember, code with out-of-date comments is worse than no comments at all!
A lot of the time, comments just says what the code does anyway, which is a waste of human effort. And if it doesn't, your code probably sucks and you should refactor it.
Just use testing frameworks.
Comment -- or better yet, recode -- anything that is non-obvious now. Later it will be completely non-obvious. You might think, "but it's going to be me," but if your way of thinking (and ways of coding) changes as you grow what's obvious to you now might not be obvious to you later.
Have you read Code Complete yet? Recommended as a very good read, and a great way to figure out some of the things CS profs drill down your throat.
Code comments come in two variety:
Comments to explain logic, making
sure that the code matches the
intent. Often people will write high
level pseudocode and will use that
in comment form to fill in the
actual code of what the module will
do. Then they leave the comments as
a read-along which can be used
during later review.
Comments to
explain usage of a module. Think
javadocs. Your intent here is for
the consumers to understand why your
code is important. One use of
javadocs is in the Visual Studio
Intellisense (since I don't use
Eclipse idk). It shows the comments
from the javadoc in the intellisense
hover. Becomes VERY handy later on.
When professors ask you to document everything in your code, I have found the usage of psuedocode translated to actual code to be sufficient. However, in practice I've not found that many devs need it, as usually the code is sufficient to explain itself (when simple, well written, not relying on tricks, and when using descriptive variable names).
But I still put in comments about intent if I think it's the least bit unclear. This is just a bit of best practice.
But I definitely say read that book. ;)
If you ever decide to open-source your personal project, people will thank you for your comments (unless they're terrible). If you hit upon a spectacularly great idea and your personal project turns into a business, then you'll be hiring more developers, and again your comments will be valuable. If you suffer a mild head injury, then when you return to work you'll be thankful for your comments.
Some people treat comments as a code smell, a sign that the code could use more descriptive names and a better structure. They will fix the code so it does not need comments.
This works in a lot of cases. However one type of comment that is useful is 'why' something is being done. Sometimes fixes are made for obscure reasons that would not be obvious when reviewing the code later. The comments should not express what the code does (that should be covered by naming) or how it does that (again, the code tells you that), so save your comments for 'why'.
I find that nothing serves as better documentation as to how something works then unit tests.
Whenever i'm doing something that isn't self-documenting, i'll put a comment. I will forget what i was doing unless i do. But i prefer to write code that's so obvious that comments don't help much. Wherever possible, the code should be clear enough that thousands of lines of comments would be unnecessary.
Whatever you do, do NOT write comments like this...
// add 1 to i
++i;
That's noise. You're actually worse off with comments like that than with none at all.
A hard-core stance is: "if you have to write a comment for your code, your code is broken". Rather than writing explanatory comments, refactor your code so that the comments become less necessary. This applies especially to function names (including their parameters), since they tend to be modified the most, and the comments seldom are updated to match.
Instead of:
// Compute average for the two times
int a = t1 + (t2 - t1) / 2;
write
int averageTime = AverageOfTimes(t1, t2);
int AverageOfTimes(int t1, int t2) {
return t1 + (t2-t1);
}
Stale comments are one of the leading causes of WTF's when I'm reading other people's code.
Overcommenting has been cited as a "code smell" by several authors, including the authors of "Clean Code".
Personally, I write an explanatory comment for each class (I code in C# and C++ mostly), and occasionally when I am using an algorithm I want to refer to.
To be honest, if code is clear its not necessary, but comments are best when a specific logic breaks given certain data (which may not be obvious). Leaving comments of issues that may occur is a great way to help prevent accidental bugs due to misunderstandings of what data to expect (or specifically not).
I used to be in the exact same situation as you. When I first started I never commented anything because everything was extremely small and I always knew how it worked. But as I continued to expand my code and everything started pointing to each other, I found myself not knowing what certain things did anymore and got lost. I had to rewrite a lot of things so I knew what they did again, and I started commenting everything so I knew exactly how it worked and how to use it in the future. You may think you know how everything works now, but in the future you'll look back at something and say 'HUH?' It's better to comment things now and save yourself the trouble later.
The way I comment things:
Always add this at the top of any function, so you know what it does.
/**
* What the function is supposed to do, a brief description of it.
*
* #param paramter_name Object-type A description of it, do for each parameter.
*
* #return Object-type - A brief description of what is being returned.
**/
Then throughout your code make sure you comment things that look complicated. When you run checks, put a quick comment like 'make sure this is valid'. For any long lines of code or large blocks of code, add a comment of what that specific section does, to easily find it later on.
Commenting is useful for individual project as well as group projects especially when you will need to maintain or enhance the code over an extended period of time. This scenario may not be applicable for school projects, but in the workplace it is definitely applicable. If you have ever had to look at code that you wrote 6 months in the past then it might as well have been written by somebody else.
I have found that--as everyone will tell you--if you are coming back to code after several months you will have forgotten everything. That said, I hardly comment my own code except for comments like // ew.. hacked because X-beyond-my-control doesn't do Y correctly. But this is because the code itself is written very cleanly and is very easy to read. For instance, all variable and function names are completely descriptive. I don't use abbreviations except for rather long words which are obvious such as 'info'. All functions are extremely brief. All functions do one thing if possible. Nesting is avoided if possible. Logically related functions are grouped via classes or modules.
When I read other people's code, I don't read the comments. I read the code. And the difference between clear and well written code and spaghetti is far more important than any comments. Usually I don't care what their intent is/was; I want to change the code. And to do that it easily it needs to be well organized. So the comments are peripheral. But perhaps this is just me.
Technically speaking the code is perfectly self documenting. I like to comment anything that is non-obvious or especially complex. I tend to like to have at minimum summary on a class, and maybe a short blurb for each member. When you have to write a huge amount of doc on a very large and complex method that is usually a good sign that it needs to be looked at for a refactor.
foreach(var a in b.Items) //Enumerate the items in "b"
{
if(a.FirstName == "Jones") //See if first name is Jones
....
You want something in the middle of the above and no commenting whatsoever.
commenting is always useful!And I dont thik that commenting is a waste of time!It helps other developeres understand your code and it helps you when you haven't work on a project for months.
University software courses often push people towards excessive commenting as a way of forcing students to think twice about what they have typed. A nasty rule-of-thumb that was put my way when I was marking undergrad coursework a few years ago suggested a comment every 5-10 lines. Think most Java courses tell you to limit methods to circa 30 lines, so lots of comments within a function is a sign you should break it up.
My personal preference is to limit comments to documenting function purpose/inputs/outputs and data structures. Otherwise comments ought to be limited to things that require particular attention (eg things that looks out of place, perhaps bugs, at first glance).
The first comments are the variables and methods names. A lot of attention shall be paid to choose them. Do not hesitate to rename them if you can think of a better name.
Consistency and convention also help. Try to avoid NumberOfStuff, ThingCount, FooSize, always use the same form, possibly something in line with the language (does it have Array.length, or Vector.size). Always name similar things with similar names.
"Code never lies. Comments sometimes do". One day or the other, someone will modify the code and not the associated comment. Better spenf more time writing self-explanatory code complemented with some clever comment, than splitting out code and then explaining things with a lot of comments.
Rule #1
Comments should indicate WHY not 'what' (the code already tells you 'what' is happening)
Rule #2
After writing the comment - rewrite your code to read like the comment (then remove the comment)
While good variable and function names etc. may lessen the need for comments, any sufficiently complex program is going to be hard to understand merely by looking at the code alone, no matter how carefully it was written.
In general, the larger the body of code and the longer you expect it to be in use, the more important it will be to write detailed comments. It is perfectly reasonable for teachers to demand detailed comments because they don't want to have to spend a lot of time trying to understand large amounts of code from different students, but you don't necessarily have to maintain that same standard outside the classroom.
Regarding commenting functions & classes and the like, I find that only the most trivial functions are so self explanatory that a comment won't save the reader some time. Also, when you are using a smart IDE for a language such as Java or Curl writing properly formatted documentation comments will allow developers to see documentation for functions and methods simply by hovering over a call signature. This can save you a lot of time when working with large systems.
As it currently stands, this question is not a good fit for our Q&A format. We expect answers to be supported by facts, references, or expertise, but this question will likely solicit debate, arguments, polling, or extended discussion. If you feel that this question can be improved and possibly reopened, visit the help center for guidance.
Closed 10 years ago.
Joining an existing team with a large codebase already in place can be daunting. What's the best approach;
Broad; try to get a general overview of how everything links together, from the code
Narrow; focus on small sections of code at a time, understanding how they work fully
Pick a feature to develop and learn as you go along
Try to gain insight from class diagrams and uml, if available (and up to date)
Something else entirely?
I'm working on what is currently an approx 20k line C++ app & library (Edit: small in the grand scheme of things!). In industry I imagine you'd get an introduction by an experienced programmer. However if this is not the case, what can you do to start adding value as quickly as possible?
--
Summary of answers:
Step through code in debug mode to see how it works
Pair up with someone more familiar with the code base than you, taking turns to be the person coding and the person watching/discussing. Rotate partners amongst team members so knowledge gets spread around.
Write unit tests. Start with an assertion of how you think code will work. If it turns out as you expected, you've probably understood the code. If not, you've got a puzzle to solve and or an enquiry to make. (Thanks Donal, this is a great answer)
Go through existing unit tests for functional code, in a similar fashion to above
Read UML, Doxygen generated class diagrams and other documentation to get a broad feel of the code.
Make small edits or bug fixes, then gradually build up
Keep notes, and don't jump in and start developing; it's more valuable to spend time understanding than to generate messy or inappropriate code.
this post is a partial duplicate of the-best-way-to-familiarize-yourself-with-an-inherited-codebase
Start with some small task if possible, debug the code around your problem.
Stepping through code in debug mode is the easiest way to learn how something works.
Another option is to write tests for the features you're interested in. Setting up the test harness is a good way of establishing what dependencies the system has and where its state resides. Each test starts with an assertion about the way you think the system should work. If it turns out to work that way, you've achieved something and you've got some working sample code to reproduce it. If it doesn't work that way, you've got a puzzle to solve and a line of enquiry to follow.
One thing that I usually suggest to people that has not yet been mentioned is that it is important to become a competent user of the existing code base before you can be a developer. When new developers come into our large software project, I suggest that they spend time becoming expert users before diving in trying to work on the code.
Maybe that's obvious, but I have seen a lot of people try to jump into the code too quickly because they are eager to start making progress.
This is quite dependent on what sort of learner and what sort of programmer you are, but:
Broad first - you need an idea of scope and size. This might include skimming docs/uml if they're good. If it's a long term project and you're going to need a full understanding of everything, I might actually read the docs properly. Again, if they're good.
Narrow - pick something manageable and try to understand it. Get a "taste" for the code.
Pick a feature - possibly a different one to the one you just looked at if you're feeling confident, and start making some small changes.
Iterate - assess how well things have gone and see if you could benefit from repeating an early step in more depth.
Pairing with strict rotation.
If possible, while going through the documentation/codebase, try to employ pairing with strict rotation. Meaning, two of you sit together for a fixed period of time (say, a 2 hour session), then you switch pairs, one person will continue working on that task while the other moves to another task with another partner.
In pairs you'll both pick up a piece of knowledge, which can then be fed to other members of the team when the rotation occurs. What's good about this also, is that when a new pair is brought together, the one who worked on the task (in this case, investigating the code) can then summarise and explain the concepts in a more easily understood way. As time progresses everyone should be at a similar level of understanding, and hopefully avoid the "Oh, only John knows that bit of the code" syndrome.
From what I can tell about your scenario, you have a good number for this (3 pairs), however, if you're distributed, or not working to the same timescale, it's unlikely to be possible.
I would suggest running Doxygen on it to get an up-to-date class diagram, then going broad-in for a while. This gives you a quickie big picture that you can use as you get up close and dirty with the code.
I agree that it depends entirely on what type of learner you are. Having said that, I've been at two companies which had very large code-bases to begin with. Typically, I work like this:
If possible, before looking at any of the functional code, I go through unit tests that are already written. These can generally help out quite a lot. If they aren't available, then I do the following.
First, I largely ignore implementation and look only at header files, or just the class interfaces. I try to get an idea of what the purpose of each class is. Second, I go one level deep into the implementation starting with what seems to be the area of most importance. This is hard to gauge, so occasionally I just start at the top and work my way down in the file list. I call this breadth-first learning. After this initial step, I generally go depth-wise through the rest of the code. The initial breadth-first look helps to solidify/fix any ideas I got from the interface level, and then the depth-wise look shows me the patterns that have been used to implement the system, as well as the different design ideas. By depth-first, I mean you basically step through the program using the debugger, stepping into each function to see how it works, and so on. This obviously isn't possible with really large systems, but 20k LOC is not that many. :)
Work with another programmer who is more familiar with the system to develop a new feature or to fix a bug. This is the method that I've seen work out the best.
I think you need to tie this to a particular task. When you have time on your hands, go for whichever approach you are in the mood for.
When you have something that needs to get done, give yourself a narrow focus and get it done.
Get the team to put you on bug fixing for two weeks (if you have two weeks). They'll be happy to get someone to take responsibility for that, and by the end of the period you will have spent so much time problem-solving with the library that you'll probably know it pretty well.
If it has unit tests (I'm betting it doesn't). Start small and make sure the unit tests don't fail. If you stare at the entire codebase at once your eyes will glaze over and you will feel overwhelmed.
If there are no unit tests, you need to focus on the feature that you want. Run the app and look at the results of things that your feature should affect. Then start looking through the code trying to figure out how the app creates the things you want to change. Finally change it and check that the results come out the way you want.
You mentioned it is an app and a library. First change the app and stick to using the library as a user. Then after you learn the library it will be easier to change.
From a top down approach, the app probably has a main loop or a main gui that controls all the action. It is worth understanding the main control flow of the application. It is worth reading the code to give yourself a broad overview of the main flow of the app. If it is a GUI app, creating a paper that shows which screens there are and how to get from one screen to another. If it is a command line app, how the processing is done.
Even in companies it is not unusual to have this approach. Often no one fully understands how an application works. And people don't have time to show you around. They prefer specific questions about specific things so you have to dig in and experiment on your own. Then once you get your specific question you can try to isolate the source of knowledge for that piece of the application and ask it.
Start by understanding the 'problem domain' (is it a payroll system? inventory? real time control or whatever). If you don't understand the jargon the users use, you'll never understand the code.
Then look at the object model; there might already be a diagram or you might have to reverse engineer one (either manually or using a tool as suggested by Doug). At this stage you could also investigate the database (if any), if should follow the object model but it may not, and that's important to know.
Have a look at the change history or bug database, if there's an area that comes up a lot, look into that bit first. This doesn't mean that it's badly written, but that it's the bit everyone uses.
Lastly, keep some notes (I prefer a wiki).
The existing guys can use it to sanity check your assumptions and help you out.
You will need to refer back to it later.
The next new guy on the team will really thank you.
I had a similar situation. I'd say you go like this:
If its a database driven application, start from the database and try to make sense of each table, its fields and then its relation to the other tables.
Once fine with the underlying store, move up to the ORM layer. Those table must have some kind of representation in code.
Once done with that then move on to how and where from these objects are coming from. Interface? what interface? Any validations? What preprocessing takes place on them before they go to the datastore?
This would familiarize you better with the system. Remember that trying to write or understand unit tests is only possible when you know very well what is being tested and why it needs to be tested in only that way.
And in case of a large application that is not driven towards databases, I'd recommend an other approach:
What the main goal of the system?
What are the major components of the system then to solve this problem?
What interactions each of the component has among them? Make a graph that depicts component dependencies. Ask someone already working on it. These componentns must be exchanging something among each other so try to figure out those as well (like IO might be returning File object back to GUI and like)
Once comfortable to this, dive into component that is least dependent among others. Now study how that component is further divided into classes and how they interact wtih each other. This way you've got a hang of a single component in total
Move to the next least dependent component
To the very end, move to the core component that typically would have dependencies on many of the other components which you've already tackled
While looking at the core component, you might be referring back to the components you examined earlier, so dont worry keep working hard!
For the first strategy:
Take the example of this stackoverflow site for instance. Examine the datastore, what is being stored, how being stored, what representations those items have in the code, how an where those are presented on the UI. Where from do they come and what processing takes place on them once they're going back to the datastore.
For the second one
Take the example of a word processor for example. What components are there? IO, UI, Page and like. How these are interacting with each other? Move along as you learn further.
Be relaxed. Written code is someone's mindset, froze logic and thinking style and it would take time to read that mind.
First, if you have team members available who have experience with the code you should arrange for them to do an overview of the code with you. Each team member should provide you with information on their area of expertise. It is usually valuable to get multiple people explaining things, because some will be better at explaining than others and some will have a better understanding than others.
Then, you need to start reading the code for a while without any pressure (a couple of days or a week if your boss will provide that). It often helps to compile/build the project yourself and be able to run the project in debug mode so you can step through the code. Then, start getting your feet wet, fixing small bugs and making small enhancements. You will hopefully soon be ready for a medium-sized project, and later, a big project. Continue to lean on your team-mates as you go - often you can find one in particular who is willing to mentor you.
Don't be too hard on yourself if you struggle - that's normal. It can take a long time, maybe years, to understand a large code base. Actually, it's often the case that even after years there are still some parts of the code that are still a bit scary and opaque. When you get downtime between projects you can dig in to those areas and you'll often find that after a few tries you can figure even those parts out.
Good luck!
You may want to consider looking at source code reverse engineering tools. There are two tools that I know of:
SWAG Kit (Linux only) link
Bauhaus academic commercial
Both tools offer similar feature sets that include static analysis that produces graphs of the relations between modules in the software.
This mostly consists of call graphs and type/class decencies. Viewing this information should give you a good picture of how the parts of the code relate to one another. Using this information, you can dig into the actual source for the parts that you are most interested in and that you need to understand/modify first.
I find that just jumping in to code can be a a bit overwhelming. Try to read as much documentation on the design as possible. This will hopefully explain the purpose and structure of each component. Its best if an existing developer can take you through it but that isn't always possible.
Once you are comfortable with the high level structure of the code, try to fix a bug or two. this will help you get to grips with the actual code.
I like all the answers that say you should use a tool like Doxygen to get a class diagram, and first try to understand the big picture. I totally agree with this.
That said, this largely depends on how well factored the code is to begin with. If its a gigantic mess, it's going to be hard to learn. If its clean, and organized properly, it shouldn't be that bad.
See this answer on how to use test coverage tools to locate the code for a feature of interest, without knowing anything about where that feature is, or how it is spread across many modules.
(shameless marketing ahead)
You should check out nWire. It is an Eclipse plugin for navigating and visualizing large codebases. Many of our customers use it to break-in new developers by printing out visualizations of the major flows.