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  • How to write constructors which might fail to properly instantiate an object

    - by whitman
    Sometimes you need to write a constructor which can fail. For instance, say I want to instantiate an object with a file path, something like obj = new Object("/home/user/foo_file") As long as the path points to an appropriate file everything's fine. But if the string is not a valid path things should break. But how? You could: 1. throw an exception 2. return null object (if your programming language allows constructors to return values) 3. return a valid object but with a flag indicating that its path wasn't set properly (ugh) 4. others? I assume that the "best practices" of various programming languages would implement this differently. For instance I think ObjC prefers (2). But (2) would be impossible to implement in C++ where constructors must have void as a return type. In that case I take it that (1) is used. In your programming language of choice can you show how you'd handle this problem and explain why?

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  • Misconceptions about purely functional languages?

    - by Giorgio
    I often encounter the following statements / arguments: Pure functional programming languages do not allow side effects (and are therefore of little use in practice because any useful program does have side effects, e.g. when it interacts with the external world). Pure functional programming languages do not allow to write a program that maintains state (which makes programming very awkward because in many application you do need state). I am not an expert in functional languages but here is what I have understood about these topics until now. Regarding point 1, you can interact with the environment in purely functional languages but you have to explicitly mark the code (functions) that introduces them (e.g. in Haskell by means of monadic types). Also, AFAIK computing by side effects (destructively updating data) should also be possible (using monadic types?) but is not the preferred way of working. Regarding point 2, AFAIK you can represent state by threading values through several computation steps (in Haskell, again, using monadic types) but I have no practical experience doing this and my understanding is rather vague. So, are the two statements above correct in any sense or are they just misconceptions about purely functional languages? If they are misconceptions, how did they come about? Could you write a (possibly small) code snippet illustrating the Haskell idiomatic way to (1) implement side effects and (2) implement a computation with state?

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  • Can higher-order functions in FP be interpreted as some kind of dependency injection?

    - by Giorgio
    According to this article, in object-oriented programming / design dependency injection involves a dependent consumer, a declaration of a component's dependencies, defined as interface contracts, an injector that creates instances of classes that implement a given dependency interface on request. Let us now consider a higher-order function in a functional programming language, e.g. the Haskell function filter :: (a -> Bool) -> [a] -> [a] from Data.List. This function transforms a list into another list and, in order to perform its job, it uses (consumes) an external predicate function that must be provided by its caller, e.g. the expression filter (\x -> (mod x 2) == 0) [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] selects all even numbers from the input list. But isn't this construction very similar to the pattern illustrated above, where the filter function is the dependent consumer, the signature (a -> Bool) of the function argument is the interface contract, the expression that uses the higher-order is the injector that, in this particular case, injects the implementation (\x -> (mod x 2) == 0) of the contract. More in general, can one relate higher-order functions and their usage pattern in functional programming to the dependency injection pattern in object-oriented languages? Or in the inverse direction, can dependency injection be compared to using some kind of higher-order function?

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  • What do you wish language designers paid attention to?

    - by Berin Loritsch
    The purpose of this question is not to assemble a laundry list of programming language features that you can't live without, or wish was in your main language of choice. The purpose of this question is to bring to light corners of languge design most language designers might not think about. So, instead of thinking about language feature X, think a little more philisophically. One of my biases, and perhaps it might be controversial, is that the softer side of engineering--the whys and what fors--are many times more important than the more concrete side. For example, Ruby was designed with a stated goal of improving developer happiness. While your opinions may be mixed on whether it delivered or not, the fact that was a goal means that some of the choices in language design were influenced by that philosophy. Please do not post: Syntax flame wars (I could care less whether you use whitespace [Python], keywords [Ruby], or curly braces [Java, C/C++, et. al.] to denote program blocks). That's just an implementation detail. "Any language that doesn't have feature X doesn't deserve to exist" type comments. There is at least one reason for all programming languages to exist--good or bad. Please do post: Philisophical ideas that language designers seem to miss. Technical concepts that seem to be poorly implemented more often than not. Please do provide an example of the pain it causes and if you have any ideas of how you would prefer it to function. Things you wish were in the platform's common library but seldom are. One the same token, things that usually are in a common library that you wish were not. Conceptual features such as built in test/assertion/contract/error handling support that you wish all programming languages would implement properly--and define properly. My hope is that this will be a fun and stimulating topic.

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  • Hobbyist transitioning to earn money on paid work?

    - by Chelonian
    I got into hobbyist Python programming some years ago on a whim, having never programmed before other than BASIC way back when, and little by little have cobbled together a, in my opinion, nice little desktop application that I might try to get out there in some fashion someday. It's roughly 15,000 logical lines of code, and includes use of Python, wxPython, SQLite, and a number of other libraries, works on Win and Linux (maybe Mac, untested) and I've gotten some good feedback about the application's virtues from non-programmer friends. I've also done a small application for data collection for animal behavior experiments, and an ad hoc tool to help generate a web page...and I've authored some tutorials. I consider my Python skills to be appreciably limited, my SQL skills to be very limited, but I'm not totally out to sea, either (e.g. I did FizzBuzz in a few minutes, did a "Monty Hall Dilemma" simulator in some minutes, etc.). I also put a strong premium on quality user experience; that is, the look and feel matters much to me and the software looks quite good, I feel. I know no other programming languages yet. I also know the basics of HTML/CSS (not considering them programming languages) and have created an artist's web page (that was described by a friend as "incredibly slick"...it's really not, though), and have a scientific background. I'm curious: Aside from directly selling my software, what's roughly possible--if anything--in terms of earning either side money on gigs, or actually getting hired at some level in the software industry, for someone with this general skill set?

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  • Do we ethically have the right to use the MAC Address for verification purposes?

    - by Matt Ridge
    I am writing a program, or starting at the very beginning of it, and I am thinking of purchase verification systems as a final step. I will be catering to Macs, PCs, and possibly Linux if all is said and done. I will also be programming this for smartphones as well using C++ and Objective-C. (I am writing a blueprint before going head first into it) That being said, I am not asking for help on doing it yet, but what I’m looking for is a realistic measurement for what could be expected as a viable and ethical option for purchase verification systems. Apple through the Apple Store, and some other stores out there have their own "You bought it" check. I am looking to use a three prong verification system. Email/password 16 to 32 character serial number using alpha/numeric and symbols with Upper and lowercase variants. MAC Address. The first two are in my mind ok, but I have to ask on an ethical standpoint, is a MAC Address to lock the software to said hardware unethical, or is it smart? I understand if an Ethernet card changes if not part of the logic board, or if the logic board changes so does the MAC address, so if that changes it will have to be re-verified, but I have to ask with how everything is today... Is it ethical to actually use the MAC address as a validation key or no? Should I be forward with this kind of verification system or should I keep it hidden as a secret? Yes I know hackers and others will find ways of knowing what I am doing, but in reality this is why I am asking. I know no verification is foolproof, but making it so that its harder to break is something I've always been interested in, and learning how to program is bringing up these questions, because I don't want to assume one thing and find out it's not really accepted in the programming world as a "you shouldn't do that" maneuver... Thanks in advance... I know this is my first programming question, but I am just learning how to program, and I am just making sure I'm not breaking some ethical programmer credo I shouldn't...

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  • How often do you review fundamentals?

    - by mlnyc
    So I've been out of school for a year and a half now. In school, of course we covered all the fundamentals: OS, databases, programming languages (i.e. syntax, binding rules, exception handling, recursion, etc), and fundamental algorithms. the rest were more in-depth topics on things like NLP, data mining, etc. Now, a year ago if you would have told me to write a quicksort, or reverse a singly-linked list, analyze the time complexity of this 'naive' algorithm vs it's dynamic programming counterpart, etc I would have been able to give you a decent and hopefully satisfying answer. But if you would have asked me more real world questions I might have been stumped (things like how would handle logging for an application, or security difference between GET and POST, differences between SQL Server and Oracle SQL, anything I list on my resume as currently working with [jQuery questions, ColdFusion questions, ...] etc) Now, I feel things are the opposite. I haven't wrote my own sort since graduating, and I don't really have to worry much about theoretical things that do not naturally fall into problems I am trying to solve. For example, I might give you some great SQL solutions using an analytical function that I would have otherwise been stumped on or write a cool web application using angular or something but ask me to write an algo for insertAfter(Element* elem) and I might not be able to do it in a reasonable time frame. I guess my question here to the experienced programmers is how do you balance the need to both learn and experiment with new technologies (fun!), working on personal projects (also fun!) working and solving real world problems in a timeboxed environment (so I might reach out to a library that does what I want rather than re-invent the wheel so that I can focus on the problem I am trying to solve) (work, basically), and refreshing on old theoretical material which is still valid for interviews and such (can be a drag)? Do you review older material (such as famous algorithms, dynamic programming, Big-O analysis, locking implementations) regularly or just when you need it? How much time do you dedicate to both in your 'deliberate practice' and do you have a certain to-do list of topics that you want to work on?

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  • What kinds of languages would be most useful for this kind of webapp?

    - by Caedar
    I've had some experience with programming in the past (2-3 years of C++ self-teaching), so I'm no stranger to the programming process, but there are so many languages out there that I'm lost when thinking about this project idea that's been floating around my head: I would like to create a webapp that would be used for helping somebody figure out what kinds of productivity tools would suit them. The first part of the app would basically be a survey with a variety of questions that would help weed out tools that wouldn't be useful for them. (Slider bar between minimalist and maximizer, slider bar between all free apps and no cost limit, checkboxes on what platforms are required, etc.) While the person is filling out the survey, they will see a web of applications, webapps, and other tools forming on the screen with links showing the relationships the programs have with eachother (syncing supported, good combinations of apps, etc.), along with a list of applications below sorted by general use (notetaking, document organization, storage, etc.) I would imagine that each program entered into the database that will be accessed would have a certain set of characteristics, ie. price, user friendliness, platforms supported, general uses, etc. and the survey would be designed to correlate to those elements and remove programs that don't match the criteria set. The difficult part of this entire process would be getting the web of applications to arrange itself and render properly. Now that I've finished mind-dumping, onto my question: What kinds/combinations of programming languages would you imagine being useful for this kind of project, and why? I learn best by setting up a project for myself like this one and tinkering with the languages, so I don't mind if the end product is out of reach from my current skill level. I'd just like some guidance so I don't fumble in the dark for too long.

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  • If you had to go back and re-learn your skill set, how would you do it?

    - by vorbb
    My younger brother is looking to start programming. He's 14, and technically-inclined, but no real experience programming. He's looking to me for guidance, and I don't feel as if my experience is enough, so I figured I'd ask here. He's more interested in web programming, but also has an interest in desktop/mobile/server applications. What would be a good learning path for him to take? I'm going to buy him a bunch of books for Christmas to get him started; the question is, what should he learn, and in which order? The way I see it, he needs to learn theory and code. I'd like to start him off with Python or Ruby or PHP. If he wants to get in to web, he's also going to need to learn HTML, CSS, Javascript, etc. Out of those three domains (Languages, Theory, Markup/Etc.), what is the best order do you think to learn in? Also, am I missing anything? Thanks!

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  • Programming doesn&rsquo;t have to be Magic

    - by Wes McClure
    In the show LOST, the Swan Station had a button that “had to be pushed” every 100 minutes to avoid disaster.  Several characters in the show took it upon themselves to have faith and religiously push the button, resetting the clock and averting the unknown “disaster”.  There are striking similarities in this story to the code we write every day.  Here are some common ones that I encounter: “I don’t know what it does but the application doesn’t work without it” “I added that code because I saw it in other similar places, I didn’t understand it, but thought it was necessary.” (for consistency, or to make things “work”) “An error message recommended it” “I copied that code” (and didn’t look at what it was doing) “It was suggested in a forum online and it fixed my problem so I left it” In all of these cases we haven’t done our due diligence to understand what the code we are writing is actually doing.  In the rush to get things done it seems like we’re willing to push any button (add any line of code) just to get our desired result and move on.  All of the above explanations are common things we encounter, and are valid ways to work through a problem we have, but when we find a solution to a task we are working on (whether a bug or a feature), we should take a moment to reflect on what we don’t understand.  Remove what isn’t necessary, comprehend and simplify what is.  Why is it detrimental to commit code we don’t understand? Perpetuates unnecessary code If you copy code that isn’t necessary, someone else is more likely to do so, especially peers Perpetuates tech debt Adding unnecessary code leads to extra code that must be understood, maintained and eventually cleaned up in longer lived projects Tech debt begets tech debt as other developers copy or use this code as guidelines in similar situations Increases maintenance How do we know the code is simplified if we don’t understand it? Perpetuates a lack of ownership Makes it seem ok to commit anything so long as it “gets the job done” Perpetuates the notion that programming is magic If we don’t take the time to understand every line of code we add, then we are contributing to the notion that it is simply enough to make the code work, regardless of how. TLDR Don’t commit code that you don’t understand, take the time to understand it, simplify it and then commit it!

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  • Programming Windows 8 Apps with HTML, CSS, and JavaScript - All you need in one title

    It took me a while to work through the 800+ pages of this title. And yes, I really mean working not reading... Since the release of Windows 8 it should be obvious to any Windows software developer that there are new ways to develop, deploy and market applications for a broader audience. Interestingly, Microsoft started to narrow the technological gap between the various platforms - desktop, web, smartphone and XBox - and development of modern apps with HTML, CSS and JavaScript couldn't be easier. Kraig covers all facets of modern Windows 8 apps from the basic building blocks and project templates in Visual Studio 2012 over to the thoughtful use of specific APIs to finally proper deployment in the App Store and potential monetization. The organisation of the book is lied out like step by step instructions or a tutorial. Kraig literally takes the reader by the hand and explains in detail in his examples about the reasons, the pros, and the cons of a certain way of implementation. Thanks to cross-references to other chapters he leaves the choice to the reader to dig deeper right now or to catch up at some time later. Personally, I have to admit that I really enjoyed the relaxed writing style. App development is not dust-dry rocket science and it should be joyful to learn about new technologies. And thanks to the richness of the various chapters and samples you could easily adapt and transfer the knowledge gained in this title to other platforms like Windows Phone 8. And last but not least: The ebook is freely available at Amazon, Microsoft Press and O'Reilly. Don't think about it, just get the book. Now. Update: I already mentioned this title in other blog entries which are related to Microsoft certification. Feel free to read on and to discover more online resources: Learning content for MCSDs: Web Applications and Windows Store Apps using HTML5 More content for MCSDs: Web Applications and Windows Store Apps using HTML5 O'Reilly offers free webcasts on their site, too. And in case that you would like to know more about Kraig's book and his experience with various development teams, please checkout this one: Zero to App in Two Weeks: Programming Windows 8 Apps in HTML, CSS, and JavaScript. The recording should be available soon.

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  • Could spending time on Programmers.SE or Stack Overflow be substitute of good programming books for a non-beginner?

    - by Atul Goyal
    Could spending time (and actively participating) on Programmers.SE and Stack Overflow help me improve my programming skills any close to what spending time on reading a book like Code Complete 2 (which would otherwise be next in my reading list) will help. Ok, may be the answer to this question for someone who is beginning with programming might be a straight no, but I'd like to add that this question I'm asking in context when the person is familiar with programming languages but wants to improve his programming skills. I was reading this question on SO and also this book has been recommended by many others (including Jeff and Joel). To be more specific, I'd also add that even though I do programming in C, Java, Python,etc but still I'm not happy with my coding skills and reading the review of CC2 I realized I still need to improve a lot. So, basically I want to know what's the best way for me to improve programming skills - spend more time on here/SO or continue with CC2 and may be come here as and when time permits.

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  • How is programming affected by spatial aptitude?

    - by natli
    The longer I work on a project, the less clear it becomes. It's like I cannot seperate various classes/objects anymore in my head. Everything starts mixing up, and it's extremely hard to take it all apart again. I start putting functions in classes where they really don't belong, and make silly mistakes such as writing code that I later find was 100% obsolete; things are no longer clearly mappable in my head. It isn't until I take a step back for several hours (or days somtimes!) that I can actually see what's going on again, and be productive. I usually try to fight through this, I am so passionate about coding that I wouldn't for the life of me know what else I could be doing. This is when stuff can get really weird, I get so up in my head that I sort of lose touch with reality (to some extent) in that various actions, such as pouring a glass of water, no longer happen on a concious level. It happens on auto pilot, during which pretty much all of my concious concentration (is that even a thing?) is devoted to borderline pointless problem solving (trying to seperate elements of code). It feels like a losing battle. So I took an IQ test a while ago (Wechsler Adult Intelligence Scale I believe it was) and it turned out my Spatial Aptitude was quite low. I still got a decent score, just above average, so I won't have to poke things with a stick for a living, but I am a little worried that this is such a handicap when writing/engineering computer programs that I won't ever be able to do it seriously or professionally. I am very much interested in what other people think of this.. could a low spatial aptitude be the cause of the above described problems? Maybe I should be looking more along the lines of ADD or something similar, because I did get diagnosed with ADD at the age of 17 (5 years ago) but the medicine I received didn't seem to affect me that much so I never took it all that serious. Sorry if I got a little off topic there, I know this is not a mental help board, the question should be clear; How is programming affected by spatial aptitude? As far as I know people are born with low/med/high spatial aptitude, so I think it's interesting to find out if the more fortunate are better programmers by birth right.

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  • Should I continue to pursue programming based on my experience?

    - by El Be
    The reason I ask this question is because I am not sure my troubles come from a lack of confidence, or something much deeper like lack of passion. I'm hoping experienced programmers and developers can help identify the cause of my troubles. To be brief my undergraduate major was in Computer Science, but in a small school and I had the highest gpa in my year in computer science. The first time I ever programmed was once in the 5th grade (using logo) and when I was a freshman in college. I enjoyed programming when I was in school. Then I did an internships where I was expected to produce image processing software and program microchips. I was unsuccessful and produced little results and I hated the job, because I had to figure out everything for myself, did not have any help, and there was a lot of pressure to produce results. Although I tried I could not figure out what to do and was stuck all the time and made me dislike the job. When the internship ended I went to a PhD program for computer science at a prestigious computer science school. I had a very hard time with the course, met people who have been programming since they were 6 and made plenty of applications in their spare time (which I never did, although I tried). I even met many sophomores who understood more than I did. The combination of this and other things have made me feel that programming is not for me, but sometimes I consider a career in programming. I still consider programming as a career because of the career potential (not only just because of money). Based on my experience do you believe my confidence has just been shaken and I should continue to prepare for a programming career, or do you see a lack of passion and it would make it tough to continue programming. thank you for reading and for your advice Thank you for everyone's advice so far! Also: I dropped out of the ph.D program for computer science and switched to a master's in computer graphics. Its more applied, but I still find it hard to be motivated (due to either lack of confidence or passion), but since programming is such a big field I am looking for that niche area that I feel good programming in.

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  • How can we improve overall Programmer Education & Training?

    - by crosenblum
    Last week, I was just viewing this amazing interview by Kevin Rose of Phillip Rosedale, of Second Life. And they had an amazing discussion about how to find, hire and identify good programmer's, and how hard it is to find good ones. Which has lead me to really think about the way we programmer's learn, are taught. For a majority of us, myself included, we are self-taught. Which is great about being a programmer, anyone can learn and develop skills. But this also means, that there is no real standards of what a good programmer is/are, and what kind of environment's encourage the growth of programming skills. This isn't so much a question, but just a desire in me, to see how we can change the culture of programming, and the manager's of programming, so that education and self-improvement is encouraged. There are a lot of avenue's for continued education, youtube videos, books, conferences, but because of the experiental nature of what we do, it isn't always clear what's important to learn and to master. Let's look at the The Joel 12 Steps. The Joel Test Do you use source control? Can you make a build in one step? Do you make daily builds? Do you have a bug database? Do you fix bugs before writing new code? Do you have an up-to-date schedule? Do you have a spec? Do programmers have quiet working conditions? Do you use the best tools money can buy? Do you have testers? Do new candidates write code during their interview? Do you do hallway usability testing? I think all of these have important value, but because of something I call the Experiential Gap, if a programmer or manager has never experienced any of the negative consequences for not having done items on the list, they will never see the need to do any of them. The Experiental Gap, is my basic theory, that each of us has different jobs and different experiences. So for some of us, that have always worked with dozens of programmer's, source control is a must have. But for people who have always been the only programmer, they can not imagine the need for source control. And it's because of this major flaw in how we learn, that we evaluate people by what best practices they do or not do, and the reason for either can start a flame war. We always evaluate people in our field by what they do, and think "Oh if this guy/gal isn't doing xyz best practice, he/she can't be a good programmer, so let's not waste time or energy talking to them." This is exactly why we have so many programming flame wars, that it becomes, because of the Experiental Gap, we can't imagine people not having made the decisions that we have had to made. So this has lead me to think, that we totally need to rethink how we train, educate and manage programmer's. For example, what percentage of you have had encouragement by your manager's to go to conferences, and even have them pay for it? For me, and a lot of people, this is extremely rare, a lot of us would love to go to conferences, to learn more, but the money ain't there to do that. So the point of this question is really to spark a lot of how can we train, learn and manage better? How can we create a new culture of learning that doesn't insult people for not having the same job experiences. Yes we all have jobs and work to do, but our ability to do our jobs well, depends on our desire, interest and support in improving our mastery of our skills. Right now, I see our culture being rather disorganized, we support the elite, but those tons of us that want to get better, just don't have enough support to learn and improve ourselves. I mean, do we as an industry, want to be perceived as just replaceable cogs? Thank you...

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  • Collision between sprites in game programming?

    - by Lyn Maxino
    I've since just started coding for an android game using eclipse. I've read Beginning Android Game Programming and various other e-books. Recently, I've encountered a problem with collision between sprites. I've used this code template for my program. package com.project.CAI_test; import java.util.Random; import android.graphics.Bitmap; import android.graphics.Canvas; import android.graphics.Rect; public class Sprite { // direction = 0 up, 1 left, 2 down, 3 right, // animation = 3 back, 1 left, 0 front, 2 right int[] DIRECTION_TO_ANIMATION_MAP = { 3, 1, 0, 2 }; private static final int BMP_ROWS = 4; private static final int BMP_COLUMNS = 3; private static final int MAX_SPEED = 5; private GameView gameView; private Bitmap bmp; private int x = 0; private int y = 0; private int xSpeed; private int ySpeed; private int currentFrame = 0; private int width; private int height; public Sprite(GameView gameView, Bitmap bmp) { this.width = bmp.getWidth() / BMP_COLUMNS; this.height = bmp.getHeight() / BMP_ROWS; this.gameView = gameView; this.bmp = bmp; Random rnd = new Random(); x = rnd.nextInt(gameView.getWidth() - width); y = rnd.nextInt(gameView.getHeight() - height); xSpeed = rnd.nextInt(MAX_SPEED * 2) - MAX_SPEED; ySpeed = rnd.nextInt(MAX_SPEED * 2) - MAX_SPEED; } private void update() { if (x >= gameView.getWidth() - width - xSpeed || x + xSpeed <= 0) { xSpeed = -xSpeed; } x = x + xSpeed; if (y >= gameView.getHeight() - height - ySpeed || y + ySpeed <= 0) { ySpeed = -ySpeed; } y = y + ySpeed; currentFrame = ++currentFrame % BMP_COLUMNS; } public void onDraw(Canvas canvas) { update(); int srcX = currentFrame * width; int srcY = getAnimationRow() * height; Rect src = new Rect(srcX, srcY, srcX + width, srcY + height); Rect dst = new Rect(x, y, x + width, y + height); canvas.drawBitmap(bmp, src, dst, null); } private int getAnimationRow() { double dirDouble = (Math.atan2(xSpeed, ySpeed) / (Math.PI / 2) + 2); int direction = (int) Math.round(dirDouble) % BMP_ROWS; return DIRECTION_TO_ANIMATION_MAP[direction]; } public boolean isCollition(float x2, float y2) { return x2 > x && x2 < x + width && y2 > y && y2 < y + height; } } The above code only detects collision between the generated sprites and the surface border. What I want to achieve is a collision detection that is controlled by the update function without having to change much of the coding. Probably several lines placed in the update() function. Tnx for any comment/suggestion.

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  • Reading graph inputs for a programming puzzle and then solving it

    - by Vrashabh
    I just took a programming competition question and I absolutely bombed it. I had trouble right at the beginning itself from reading the input set. The question was basically a variant of this puzzle http://codercharts.com/puzzle/evacuation-plan but also had an hour component in the first line(say 3 hours after start of evacuation). It reads like this This puzzle is a tribute to all the people who suffered from the earthquake in Japan. The goal of this puzzle is, given a network of road and locations, to determine the maximum number of people that can be evacuated. The people must be evacuated from evacuation points to rescue points. The list of road and the number of people they can carry per hour is provided. Input Specifications Your program must accept one and only one command line argument: the input file. The input file is formatted as follows: the first line contains 4 integers n r s t n is the number of locations (each location is given by a number from 0 to n-1) r is the number of roads s is the number of locations to be evacuated from (evacuation points) t is the number of locations where people must be evacuated to (rescue points) the second line contains s integers giving the locations of the evacuation points the third line contains t integers giving the locations of the rescue points the r following lines contain to the road definitions. Each road is defined by 3 integers l1 l2 width where l1 and l2 are the locations connected by the road (roads are one-way) and width is the number of people per hour that can fit on the road Now look at the sample input set 5 5 1 2 3 0 3 4 0 1 10 0 2 5 1 2 4 1 3 5 2 4 10 The 3 in the first line is the additional component and is defined as the number of hours since the resuce has started which is 3 in this case. Now my solution was to use Dijisktras algorithm to find the shortest path between each of the rescue and evac nodes. Now my problem started with how to read the input set. I read the first line in python and stored the values in variables. But then I did not know how to store the values of the distance between the nodes and what DS to use and how to input it to say a standard implementation of dijikstras algorithm. So my question is two fold 1.) How do I take the input of such problems? - I have faced this problem in quite a few competitions recently and I hope I can get a simple code snippet or an explanation in java or python to read the data input set in such a way that I can input it as a graph to graph algorithms like dijikstra and floyd/warshall. Also a solution to the above problem would also help. 2.) How to solve this puzzle? My algorithm was: Find shortest path between evac points (in the above example it is 14 from 0 to 3) Multiply it by number of hours to get maximal number of saves Also the answer given for the variant for the input set was 24 which I dont understand. Can someone explain that also. UPDATE: I get how the answer is 14 in the given problem link - it seems to be just the shortest path between node 0 and 3. But with the 3 hour component how is the answer 24 UPDATE I get how it is 24 - its a complete graph traversal at every hour and this is how I solve it Hour 1 Node 0 to Node 1 - 10 people Node 0 to Node 2- 5 people TotalRescueCount=0 Node 1=10 Node 2= 5 Hour 2 Node 1 to Node 3 = 5(Rescued) Node 2 to Node 4 = 5(Rescued) Node 0 to Node 1 = 10 Node 0 to Node 2 = 5 Node 1 to Node 2 = 4 TotalRescueCount = 10 Node 1 = 10 Node 2= 5+4 = 9 Hour 3 Node 1 to Node 3 = 5(Rescued) Node 2 to Node 4 = 5+4 = 9(Rescued) TotalRescueCount = 9+5+10 = 24 It hard enough for this case , for multiple evac and rescue points how in the world would I write a pgm for this ?

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  • Why subnet mask for IP 10.0.1.4 is 255.255.255.0?

    - by Rohit Kandhal
    Well I'm not sure whether I'm missing something here. But all I've read is that if first octet of IP is within 0 - 127 then it is categorized as Class A subnet and correspondingly Subnet Mask for this is 255.0.0.0 but when I connect my system to Apple airport then my system gets IP as 10.0.1.4 however subnet mask is 255.255.255.0 not 255.0.0.0. Please explain what I'm missing here. If there is something like for apple router subnet mask is calculated on some different flags then please let me know.

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  • Time values not saving in Airport Base Station MAC Timed Access List

    - by Boiler Bill
    I have an airport base station model A1354. I am attempting to setup MAC Timed Access so a laptop can only connect between 5:00AM and 11:00pm through the Airport Utility version 5.5.2 (552.11). My AEBS is running firmware version 7.5.2 When I try to enter the time values by double clicking over the time and entering 05:00 AM and 11:00PM the time values don't stay as soon as it looses focus. Instead they become what is in the following screenshot, and the laptop looses connectivity as soon as I update the base station. I also tried entering the values in military time with the same result. Any base station power users out there that know how I can get the time values to "stick"?

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  • Windows 7 x64: 3900mb of 4gb RAM usage, even when (almost) nothing running.

    - by user34630
    As the title suggests, I am having a problem with memory usage. I have had my computer (Vaio AW11Z/B laptop) for over a year now, and it was running perfectly until I guess a day or two ago. Now programs randomly crash, the mouse lags around the screen and the memory usage is going through the roof for no apparent reason. I am having exactly the same problem as this guy: http://social.answers.microsoft.com/Forums/en-US/w7performance/thread/1f716693-0a46-473e-9dc0-8c2b1a058443/. I think he explains it better. Anyone had a similar issue? What's going on? I don't think it's a virus/adware thing. Thanks very much for any help.

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  • How did you get your first programming job?

    - by Gaz
    Hi All, I have some commercial programming experience although it was not my primary role (C# and Java), SCJP 6 cert, some SQL experience and have been doing a lot of Android programming (I have one app with 36,000 downloads). I have a degree in Chemistry and a Diploma in Programming (half a degree made up of 2nd/3rd year uni courses). I'm trying to get my first entry level programmer job but am finding it tough out there.......How did other people get there first jobs in programming?

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  • An Alphabet of Eponymous Aphorisms, Programming Paradigms, Software Sayings, Annoying Alliteration

    - by Brian Schroer
    Malcolm Anderson blogged about “Einstein’s Razor” yesterday, which reminded me of my favorite software development “law”, the name of which I can never remember. It took much Wikipedia-ing to find it (Hofstadter’s Law – see below), but along the way I compiled the following list: Amara’s Law: We tend to overestimate the effect of a technology in the short run and underestimate the effect in the long run. Brook’s Law: Adding manpower to a late software project makes it later. Clarke’s Third Law: Any sufficiently advanced technology is indistinguishable from magic. Law of Demeter: Each unit should only talk to its friends; don't talk to strangers. Einstein’s Razor: “Make things as simple as possible, but not simpler” is the popular paraphrase, but what he actually said was “It can scarcely be denied that the supreme goal of all theory is to make the irreducible basic elements as simple and as few as possible without having to surrender the adequate representation of a single datum of experience”, an overly complicated quote which is an obvious violation of Einstein’s Razor. (You can tell by looking at a picture of Einstein that the dude was hardly an expert on razors or other grooming apparati.) Finagle's Law of Dynamic Negatives: Anything that can go wrong, will—at the worst possible moment. - O'Toole's Corollary: The perversity of the Universe tends towards a maximum. Greenspun's Tenth Rule: Any sufficiently complicated C or Fortran program contains an ad hoc, informally-specified, bug-ridden, slow implementation of half of Common Lisp. (Morris’s Corollary: “…including Common Lisp”) Hofstadter's Law: It always takes longer than you expect, even when you take into account Hofstadter's Law. Issawi’s Omelet Analogy: One cannot make an omelet without breaking eggs - but it is amazing how many eggs one can break without making a decent omelet. Jackson’s Rules of Optimization: Rule 1: Don't do it. Rule 2 (for experts only): Don't do it yet. Kaner’s Caveat: A program which perfectly meets a lousy specification is a lousy program. Liskov Substitution Principle (paraphrased): Functions that use pointers or references to base classes must be able to use objects of derived classes without knowing it Mason’s Maxim: Since human beings themselves are not fully debugged yet, there will be bugs in your code no matter what you do. Nils-Peter Nelson’s Nil I/O Rule: The fastest I/O is no I/O.    Occam's Razor: The simplest explanation is usually the correct one. Parkinson’s Law: Work expands so as to fill the time available for its completion. Quentin Tarantino’s Pie Principle: “…you want to go home have a drink and go and eat pie and talk about it.” (OK, he was talking about movies, not software, but I couldn’t find a “Q” quote about software. And wouldn’t it be cool to write a program so great that the users want to eat pie and talk about it?) Raymond’s Rule: Computer science education cannot make anybody an expert programmer any more than studying brushes and pigment can make somebody an expert painter.  Sowa's Law of Standards: Whenever a major organization develops a new system as an official standard for X, the primary result is the widespread adoption of some simpler system as a de facto standard for X. Turing’s Tenet: We shall do a much better programming job, provided we approach the task with a full appreciation of its tremendous difficulty, provided that we respect the intrinsic limitations of the human mind and approach the task as very humble programmers.  Udi Dahan’s Race Condition Rule: If you think you have a race condition, you don’t understand the domain well enough. These rules didn’t exist in the age of paper, there is no reason for them to exist in the age of computers. When you have race conditions, go back to the business and find out actual rules. Van Vleck’s Kvetching: We know about as much about software quality problems as they knew about the Black Plague in the 1600s. We've seen the victims' agonies and helped burn the corpses. We don't know what causes it; we don't really know if there is only one disease. We just suffer -- and keep pouring our sewage into our water supply. Wheeler’s Law: All problems in computer science can be solved by another level of indirection... Except for the problem of too many layers of indirection. Wheeler also said “Compatibility means deliberately repeating other people's mistakes.”. The Wrong Road Rule of Mr. X (anonymous): No matter how far down the wrong road you've gone, turn back. Yourdon’s Rule of Two Feet: If you think your management doesn't know what it's doing or that your organisation turns out low-quality software crap that embarrasses you, then leave. Zawinski's Law of Software Envelopment: Every program attempts to expand until it can read mail. Zawinski is also responsible for “Some people, when confronted with a problem, think 'I know, I'll use regular expressions.' Now they have two problems.” He once commented about X Windows widget toolkits: “Using these toolkits is like trying to make a bookshelf out of mashed potatoes.”

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  • Quadratic Programming with Oracle R Enterprise

    - by Jeff Taylor-Oracle
         I wanted to use quadprog with ORE on a server running Oracle Solaris 11.2 on a Oracle SPARC T-4 server For background, see: Oracle SPARC T4-2 http://docs.oracle.com/cd/E23075_01/ Oracle Solaris 11.2 http://www.oracle.com/technetwork/server-storage/solaris11/overview/index.html quadprog: Functions to solve Quadratic Programming Problems http://cran.r-project.org/web/packages/quadprog/index.html Oracle R Enterprise 1.4 ("ORE") 1.4 http://www.oracle.com/technetwork/database/options/advanced-analytics/r-enterprise/ore-downloads-1502823.html Problem: path to Solaris Studio doesn't match my installation: $ ORE CMD INSTALL quadprog_1.5-5.tar.gz * installing to library \u2018/u01/app/oracle/product/12.1.0/dbhome_1/R/library\u2019 * installing *source* package \u2018quadprog\u2019 ... ** package \u2018quadprog\u2019 successfully unpacked and MD5 sums checked ** libs /opt/SunProd/studio12u3/solarisstudio12.3/bin/f95 -m64   -PIC  -g  -c aind.f -o aind.o bash: /opt/SunProd/studio12u3/solarisstudio12.3/bin/f95: No such file or directory *** Error code 1 make: Fatal error: Command failed for target `aind.o' ERROR: compilation failed for package \u2018quadprog\u2019 * removing \u2018/u01/app/oracle/product/12.1.0/dbhome_1/R/library/quadprog\u2019 $ ls -l /opt/solarisstudio12.3/bin/f95 lrwxrwxrwx   1 root     root          15 Aug 19 17:36 /opt/solarisstudio12.3/bin/f95 -> ../prod/bin/f90 Solution: a symbolic link: $ sudo mkdir -p /opt/SunProd/studio12u3 $ sudo ln -s /opt/solarisstudio12.3 /opt/SunProd/studio12u3/ Now, it is all good: $ ORE CMD INSTALL quadprog_1.5-5.tar.gz * installing to library \u2018/u01/app/oracle/product/12.1.0/dbhome_1/R/library\u2019 * installing *source* package \u2018quadprog\u2019 ... ** package \u2018quadprog\u2019 successfully unpacked and MD5 sums checked ** libs /opt/SunProd/studio12u3/solarisstudio12.3/bin/f95 -m64   -PIC  -g  -c aind.f -o aind.o /opt/SunProd/studio12u3/solarisstudio12.3/bin/ cc -xc99 -m64 -I/usr/lib/64/R/include -DNDEBUG -KPIC  -xlibmieee  -c init.c -o init.o /opt/SunProd/studio12u3/solarisstudio12.3/bin/f95 -m64  -PIC -g  -c -o solve.QP.compact.o solve.QP.compact.f /opt/SunProd/studio12u3/solarisstudio12.3/bin/f95 -m64  -PIC -g  -c -o solve.QP.o solve.QP.f /opt/SunProd/studio12u3/solarisstudio12.3/bin/f95 -m64   -PIC  -g  -c util.f -o util.o /opt/SunProd/studio12u3/solarisstudio12.3/bin/ cc -xc99 -m64 -G -o quadprog.so aind.o init.o solve.QP.compact.o solve.QP.o util.o -xlic_lib=sunperf -lsunmath -lifai -lsunimath -lfai -lfai2 -lfsumai -lfprodai -lfminlai -lfmaxlai -lfminvai -lfmaxvai -lfui -lfsu -lsunmath -lmtsk -lm -lifai -lsunimath -lfai -lfai2 -lfsumai -lfprodai -lfminlai -lfmaxlai -lfminvai -lfmaxvai -lfui -lfsu -lsunmath -lmtsk -lm -L/usr/lib/64/R/lib -lR installing to /u01/app/oracle/product/12.1.0/dbhome_1/R/library/quadprog/libs ** R ** preparing package for lazy loading ** help *** installing help indices   converting help for package \u2018quadprog\u2019     finding HTML links ... done     solve.QP                                html      solve.QP.compact                        html  ** building package indices ** testing if installed package can be loaded * DONE (quadprog) ====== Here is an example from http://cran.r-project.org/web/packages/quadprog/quadprog.pdf > require(quadprog) > Dmat <- matrix(0,3,3) > diag(Dmat) <- 1 > dvec <- c(0,5,0) > Amat <- matrix(c(-4,-3,0,2,1,0,0,-2,1),3,3) > bvec <- c(-8,2,0) > solve.QP(Dmat,dvec,Amat,bvec=bvec) $solution [1] 0.4761905 1.0476190 2.0952381 $value [1] -2.380952 $unconstrained.solution [1] 0 5 0 $iterations [1] 3 0 $Lagrangian [1] 0.0000000 0.2380952 2.0952381 $iact [1] 3 2 Here, the standard example is modified to work with Oracle R Enterprise require(ORE) ore.connect("my-name", "my-sid", "my-host", "my-pass", 1521) ore.doEval(   function () {     require(quadprog)   } ) ore.doEval(   function () {     Dmat <- matrix(0,3,3)     diag(Dmat) <- 1     dvec <- c(0,5,0)     Amat <- matrix(c(-4,-3,0,2,1,0,0,-2,1),3,3)     bvec <- c(-8,2,0)    solve.QP(Dmat,dvec,Amat,bvec=bvec)   } ) $solution [1] 0.4761905 1.0476190 2.0952381 $value [1] -2.380952 $unconstrained.solution [1] 0 5 0 $iterations [1] 3 0 $Lagrangian [1] 0.0000000 0.2380952 2.0952381 $iact [1] 3 2 Now I can combine the quadprog compute algorithms with the Oracle R Enterprise Database engine functionality: Scale to large datasets Access to tables, views, and external tables in the database, as well as those accessible through database links Use SQL query parallel execution Use in-database statistical and data mining functionality

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  • Scala programming language for beginners, is it a legend?

    - by ali
    Hi every one, I am Ali from Saudi Arabia. undoubtedly, Scala is one of the best programming language for any programmer to learn, but there is "good" problems that is faced especially by beginners, and what seems frustrating that these problems won't solve soon, so as a beginner and on behalf of beginners let me raise these "objective" questions: 1- why scala has no effective and stable development platform, in fact, it suffers many problems with Eclipse, Netbeat, and Intellij. 2- although I have looked for a clear,easy, and understandable explanation of how to get started with Scala, but fortunately, there was no article or guide that deserves to spend the time I have spent to read it. nobody could tell you clear steps that fit you as a beginner who wants to start his"HELLO WORLD" with Scala, while all other languages have its "HELLO WORLD" guides and books. thank you for your time, be sure that you read notes below. 1- I have no experience in programming language before. 2- don't tell me "not to begin with scala", simply, because I will do. 3- OS is windows vista home premium. 4- I hate excuses, such as Scala is new language......etc

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  • Programming texts and reference material for my Kindle DX, creating the ultimate reference device?

    - by mwilliams
    (Revisiting this topic with the release of the Kindle DX) Having owned both generation Kindle readers and now getting a Kindle DX; I'm very excited for true PDF handling on an e-ink device! An image of _Why's book on my Kindle (from my iPhone). This gives me a device capable of storing hundreds of thousands of pages that are full text search capable in the form factor of a magazine. What references (preferably PDF to preserve things such as code samples) would you recommend? Ultimately I would like reference material for every modern and applicable programming language (C, C++, Objective-C, Python, Ruby, Java, .NET (C#, Visual Basic, ASP.NET), Erlang, SQL references) as well as general programming texts and frameworks (algorithms, design patterns, theory, Rails, Django, Cocoa, ORMs, etc) and anything else that could be thought of. With so many developers here using such a wide array of languages, as a professional in your particular field, what books or references would you recommend to me for my Kindle? Creative Commons material a plus (translate that to free) as well as the material being in the PDF file format. File size is not an issue. If this turns out to be a success, I will update with a follow-up with a compiled list generated from all of the answers. Thanks for the assistance and contributing! UPDATE I have been using the Kindle DX a lot now for technical books. Check out this blog post I did for high resolution photos of different material: http://www.matthewdavidwilliams.com/2009/06/12/technical-document-pdfs-on-the-kindle-dx/

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