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  • Running an RMI registry on one computer and connecting to it from another

    - by Hippopotamus
    Hello. I am doing a student assignment, using java RMI. I've programmed a simple RMI-server application that provides method which return some strings to the client. When I start the server on localhost and connect to it by client on the same computer, everything goes well. However, I am not able to do this between two computers on home network. The computers both have no trouble of connecting by a simple C program with similar functionality, so I guess the problem is with JVM here. I am binding the class to rmiregistry with try{ ComputeImpl R = new ComputeImpl(); Naming.rebind("rmi://localhost/ComputeService",R); } catch(Exception e){ System.out.println("Trouble: " +e); } And I'm doing the lookup for RMI registry in the client application with providing the argument while launching the application: StringBuffer rmi_address = new StringBuffer(); rmi_address.append("rmi://").append(args[1]).append("/ComputeService"); Compute R = (Compute) Naming.lookup(rmi_address.toString()); Is the problem with my code or with JVM? Thanks in advance.

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  • Best (Java) book for understanding 'under the bonnet' for programming?

    - by Ben
    What would you say is the best book to buy to understand exactly how programming works under the hood in order to increase performance? I've coded in assembly at university, I studied computer architecture and I obviously did high level programming, but what I really dont understand is things like: -what is happening when I perform a cast -whats the difference in performance if I declare something global as opposed to local? -How does the memory layout for an ArrayList compare with a Vector or LinkedList? -Whats the overhead with pointers? -Are locks more efficient than using synchronized? -Would creating my own array using int[] be faster than using ArrayList -Advantages/disadvantages of declaring a variable volatile I have got a copy of Java Performance Tuning but it doesnt go down very low and it contains rather obvious things like suggesting a hashmap instead of using an ArrayList as you can map the keys to memory addresses etc. I want something a bit more Computer Sciencey, linking the programming language to what happens with the assembler/hardware. The reason im asking is that I have an interview coming up for a job in High Frequency Trading and everything has to be as efficient as possible, yet I cant remember every single possible efficiency saving so i'd just like to learn the fundamentals. Thanks in advance

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  • How do software events work internally?

    - by Duddle
    Hello! I am a student of Computer Science and have learned many of the basic concepts of what is going on "under the hood" while a computer program is running. But recently I realized that I do not understand how software events work efficiently. In hardware, this is easy: instead of the processor "busy waiting" to see if something happened, the component sends an interrupt request. But how does this work in, for example, a mouse-over event? My guess is as follows: if the mouse sends a signal ("moved"), the operating system calculates its new position p, then checks what program is being drawn on the screen, tells that program position p, then the program itself checks what object is at p, checks if any event handlers are associated with said object and finally fires them. That sounds terribly inefficient to me, since a tiny mouse movement equates to a lot of cpu context switches (which I learned are relatively expensive). And then there are dozens of background applications that may want to do stuff of their own as well. Where is my intuition failing me? I realize that even "slow" 500MHz processors do 500 million operations per second, but still it seems too much work for such a simple event. Thanks in advance!

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  • Moving Computer Player in Xcode

    - by user1631497
    I am working on a 2d game using xcode and objective-c. I am trying to make my enemy player move left if I am left of him, until he is touching my character. The same will go when I am right of him. Basically just trying to get him to move towards me. But my code to do so is not working. So I have my code that says the following -(void)moveTowardsCharacter { enemyLeftTimer = [NSTimer scheduledTimerWithTimeInterval:0.05 target:self selector:@selector(goEnemyLeft) userInfo:nil repeats:YES]; if (enemyLeftTimer == nil){ enemyLeftTimer = [NSTimer scheduledTimerWithTimeInterval:0.05 target:self selector:@selector(goEnemyLeft) userInfo:nil repeats:YES]; } } -(IBAction)enemyStopLeft { if (CGRectIntersectsRect(bluebox.frame, redbox.frame)) { [enemyLeftTimer invalidate]; enemyLeftTimer = nil; } } -(void)goEnemyLeft { if (redbox.center.x + [self getRedboxWidthLeft] > bluebox.center.x + [self getBlueboxWidthRight]) { redbox.center = CGPointMake(redbox.center.x -5, redbox.center.y); } } So the first bit is saying for it to set up a timer to continue moving left. The next will stop the timer if my player(bluebox) and the Computer player(redbox) collide. Finally, the thing that actually tells it to go left, but only if the bluebox is left of the redbox. The getRedBoxWidth Left and getBlueBoxWidthRight are just voids that get, well, the left and right edges. If you could, please help try and solve this code. Thank You.

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  • Scared of Calculus - Required to pass Differential Calculus as part of my Computer science major

    - by ke3pup
    Hi guys I'm finishing my Computer science degree in university but my fear of maths (lack of background knowledge) made me to leave all my maths units til' the very end which is now. i either take them on and pass or have to give up. I've passed all my programming units easily but knowing my poor maths skills won't do i've been staying clear of the maths units. I have to pass Differential Calculus and Linear Algebra first. With a help of book named "Linear Algebra: A Modern Introduction" i'm finding myself on track and i think i can pass the Linear Algebra unit. But with differential calculus i can't find a book to help me. They're either too advanced or just too simple for what i have to learn. The things i'm required to know for this units are: Set notation, the real number line, Complex numbers in cartesian form. Complex plane, modulus. Complex numbers in polar form. De Moivre’s Theorem. Complex powers and nth roots. Definition of ei? and ez for z complex. Applications to trigonometry. Revision of domain and range of a function Working in R3. Curves and surfaces. Functions of 2 variables. Level curves.Partial derivatives and tangent planes. The derivative as a difference quotient. Geometric significance of the derivative. Discussion of limit. Higher order partial derivatives. Limits of f(x,y). Continuity. Maxima and minima of f(x,y). The chain rule. Implicit differentiation. Directional derivatives and the gradient. Limit laws, l’Hoˆpital’s rule, composition law. Definition of sinh and cosh and their inverses. Taylor polynomials. The remainder term. Taylor series. Is there a book to help me get on track with the above? Being a student i can't buy too many books hence why i'm looking for a book that covers topics I need to know. The University library has a fairly limited collection which i took as loan but didn't find useful as it was too complex.

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  • Having to hit the site login button twice after first turning on computer

    - by John
    Hello, The code below is for a login that I'm using. It works fine, but when I first try logging in after turning on my computer, it only works the second time that I hit the "Login" button. Any idea how I can make it not require hitting the "Login" button twice in this situation? Thanks in advance, John function isLoggedIn() { if (session_is_registered('loginid') && session_is_registered('username')) { return true; // the user is loged in } else { return false; // not logged in } return false; } if (!isLoggedIn()) { if (isset($_POST['cmdlogin'])) { if (checkLogin($_POST['username'], $_POST['password'])) { show_userbox(); } else { echo "Incorrect Login information !"; show_loginform(); } } else { show_loginform(); } } else { show_userbox(); } function show_loginform($disabled = false) { echo '<form name="login-form" id="login-form" method="post" action="./index.php"> <div class="usernameformtext"><label title="Username">Username: </label></div> <div class="usernameformfield"><input tabindex="1" accesskey="u" name="username" type="text" maxlength="30" id="username" /></div> <div class="passwordformtext"><label title="Password">Password: </label></div> <div class="passwordformfield"><input tabindex="2" accesskey="p" name="password" type="password" maxlength="15" id="password" /></div> <div class="registertext"><a href="http://www...com/sandbox/register.php" title="Register">Register</a></div> <div class="lostpasswordtext"><a href="http://www...com/sandbox/lostpassword.php" title="Lost Password">Lost password?</a></div> <p class="loginbutton"><input tabindex="3" accesskey="l" type="submit" name="cmdlogin" value="Login" '; if ($disabled == true) { echo 'disabled="disabled"'; } echo ' /></p></form>'; } EDIT: Here is another function that is used. function isLoggedIn() { if (session_is_registered('loginid') && session_is_registered('username')) { return true; // the user is loged in } else { return false; // not logged in } return false; }

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  • How do you differentiate between "box," "machine," "computer" and whatever else?

    - by Corey
    There seems to be a few terms for referring to a computer, especially in the tech world. Different terms seem to be used based on technical expertise. When talking with people with some technical knowledge, I'll refer to it as a machine. When talking to non-technical people (family, friends) I'll call it a computer. On the rare occasion I'm talking about servers, I might call it a box, but even then I'll probably still call it a machine. Is that just me, or do there exist rules already for what to call a computer?

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  • Do employers hiring for software jobs care about the classes you took in a Computer Science Masters program?

    - by Bob Dole
    I'm torn between two classes right now for next semester (Software Design and Advanced Computer Graphics). I would enjoy Advanced Computer Graphics more, but I feel the software design class would help me when approaching anything I ever build for the rest of my career. I feel though I could just buy the book (I already have both books actually) of the Software Design class and go through it, if I wanted. But think it would be a bit tougher to pick up the Advanced Computer Graphics class on my own. So do employers look at the graduate classes you've taken to decide if you would be a good fit or not? I think, more importantly, what I'm wanting to know is if I wanted to work for a high-end software company like Apple or Google would a company like that be more impressed by someone that took software engineering classes or hardcore CS classes?

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  • How do I make the 'Shut Down the Computer' window be monochrome ?

    - by Agmenor
    When I hit the power button of my computer, a window titled 'Shut Down the Computer' appears. It gives a few options, including shutting down or restarting. This window is different following the context I hit the power button : when logged in and seeing my desktop, it includes colourful icons (red for shutting down, for example). when I am not logged in yet, the icons are monochrome and a little bit more stylized. I clearly prefer the last type of icons : how do I set them as default whatever the context of use of the 'Shut Down the Computer' window ?

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  • How can I copy an XP Mode virtual machine from one computer to another?

    - by Investor5555
    Is it possible to copy an XP Mode Virtual PC image from one computer to a completely different computer (not on the network, not related in any way whatsoever)? I tried this, but it only would seem to work on the same computer: http://www.sevenforums.com/tutorials/21904-virtual-xp-machine-copy.html When I copy it to another computer and modify the settings as described above, the cursor just jumps around all over the screen and never starts.

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  • Software to draw 3D geometry

    - by ilovekonoka
    Does anyone know any software that can draw 3D geometry like figures usually seen in computer graphics papers and articles(example: http://www.iquilezles.org/www/articles/sphereao/sphereao.htm)? I know it can be done in Inskcape or Illustrator but I'm not sure they're the only choices.

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  • Has anyone "learned how to program in 21 days?"

    - by Sheehan Alam
    I'm not a fan of these learn how to program in X amount of days books. Some even boast, learn how to program in 24 hours. This is a joke and an insult to me as a software engineer who went through a rigorous discipline in computer science and mathematics. So a question to the community, have you benefited from these become a programmer quick books?

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  • P-NP-Problem: What are the most promising methods?

    - by phimuemue
    Hello everybody, I know that P=NP has not been solved up to now, but can anybody tell me something about the following: What are currently the most promising mathematical / computer scientific methods that could be helpful to tackle this problem? Or are there even none such methods known to be potentially helpful up to now? Is there any (free) compendium on this topic where I can find all / most of the research done in this area?

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  • P=NP?-Problem: What are the most promising methods?

    - by phimuemue
    Hello everybody, I know that P=NP has not been solved up to now, but can anybody tell me something about the following: What are currently the most promising mathematical / computer scientific methods that could be helpful to tackle this problem? Or are there even none such methods known to be potentially helpful up to now? Is there any (free) compendium on this topic where I can find all / most of the research done in this area?

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  • Need help fixing a strange path error in bash

    - by Evan
    UPDATE Ok, I found some errors in the path which I think I fixed, but now it's not running in any case - which for some reason I think is a step forward. Thanks for suggesting the following steps, here is their output: user@computer:~$ echo $PATH /usr/share/fsl/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/bin:/usr/bin:/bin:/usr/bin/X11:/usr/games:/usr/local/matlab/bin:/usr/local/VoxBo/bin:/usr/local/itt/idl64/bin:/usr/local/afni/bin/:/usr/local/mricron:/usr/lib/voxbo/bin:/home/user/folder:/usr/local/bin:/usr/bin:/bin:/usr/bin/X11/:/usr/games/:/usr/local/matlab/bin:/usr/local/VoxBo/bin/:/usr/local/itt/idl64/bin:/usr/local/afni/bin/:/usr/local/mricron/ user@computer:~$ typeset -p PATH declare -x PATH="/usr/share/fsl/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/bin:/usr/bin:/bin:/usr/bin/X11:/usr/games:/usr/local/matlab/bin:/usr/local/VoxBo/bin:/usr/local/itt/idl64/bin:/usr/local/afni/bin/:/usr/local/mricron:/usr/lib/voxbo/bin:/home/user/folder:/usr/local/bin:/usr/bin:/bin:/usr/bin/X11/:/usr/games/:/usr/local/matlab/bin:/usr/local/VoxBo/bin/:/usr/local/itt/idl64/bin:/usr/local/afni/bin/:/usr/local/mricron/" user@computer:~$ type app1 app1 is /home/user/folder/app1 user@computer:~$ type app2 app2 is /home/user/folder/app2 user@computer:~$ app1 bash: /home/user/folder/app1: No such file or directory user@computer:~$ app2 bash: /home/user/folder/app2: No such file or directory user@computer:~$ /home/user/folder/app1 bash: /home/user/folder/app1: No such file or directory user@computer:~$ /home/user/folder/app2 bash: /home/user/folder/app2: No such file or directory user@computer:~$ cd /home/user/folder user@computer:~/folder$ app1 bash: /home/user/folder/app1: No such file or directory user@computer:~/folder$ ./app1 bash: ./app1: No such file or directory user@computer:~/folder$ ./app2 bash: ./app2: No such file or directory user@computer:~/folder$ ls -l total 29384 -rwxr-xr-x 1 user user 14949776 2011-02-03 11:09 app1 -rwxr-xr-x 1 user user 15137300 2011-02-03 11:10 app2 user@computer:~/folder$ Thanks for everyone's input! ORIGINAL QUESTION I have two executable files I downloaded and am trying to add to the path. They are located in /home/user/folder and the specific files are /home/user/folder/app1 /home/user/folder/app2 Both app1 and app2 have the executable flag set to all (user, group, other). I can execute the files if I am in /home/user/folder and I execute these commands ./app1 ./app2 However I can't run them from elsewhere. I added this line to my .profile PATH="$PATH:/home/user/folder" and then sourced the path with . /home/user/.profile and I can see app1 and app2 when I use command completion (pressing tab). However here is what happens when I try to run app1 or app2 with the following commands (the following only shows 'app1' but the same is true of 'app2') user@comp:~$ app1 -bash: app1: command not found user@comp:~$ /home/user/folder/app1 -bash: app1: command not found user@comp:~/folder$ ./app1 (program runs) I'm stumped :), I must have missed something simple. Thanks for your help!!

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  • How to use multiple SkyDrive accounts on one computer?

    - by user1563721
    Is there any way how to use multiple SkyDrive accounts on one computer running MAC OS X or Windows 8? I would like to sync data from different accounts to different folder and not to merge these accounts to one. The reason is that every SkyDrive has it's storage limits and I'm using every account for different work data. The result should be the following: I have a number of SkyDrive accounts every for different work, let's say: S1 S2 S3 I would like to sync exactly the same number of folders on computer using different accounts to sync them: SkyDriveS1Folder - (folder on computer which syncing the content of S1 SkyDrive) SkyDriveS2Folder - (folder on computer which syncing the content of S2 SkyDrive) SkyDriveS3Folder - (folder on computer which syncing the content of S3 SkyDrive) Is it possible somehow? I found a workaround for Windows machines (http://superuser.com/questions/525932/running-multiple-instances-of-microsoft-skydrive) but is there anything for MAC OS X machines? Or is it possible through any third party application?

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  • Win7 Prof. Computer won't wake on lan via Magic Packet from outside network

    - by Michael
    Hi all. I just purchased a new computer running Windows 7 Professional x64. I'd like to save power by having it sleep after an hour, but I would also like to be able to Remote Desktop into it at my leisure. I set up a static IP and have port forwarding set up on the router. If the computer is awake, the RDP connection works just fine. I downloaded and installed Wake-On-Lan thanks to this article If I put my new computer to sleep and send the magic packet from my old computer inside of my home network it wakes up. If I do the same thing, however, from my work computer outside the network it does not. I figured the Firewall was blocking the incoming traffic, but nothing in the Windows Firewall logs points to this happening. I'm wondering if anyone has any suggestions or any tests I can run through in order to narrow down what the problem might be. Thanks in advance for any help you might be able to offer.

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  • Transfer hard-drive with windows XP to another computer. On booting, asks to activate xp

    - by Jesse
    I had an old computer sitting around that I have not been able to boot successfully. I moved the hard drive and placed it in my newer computer. If I boot linux, I can mount the XP hard-drive and access the files. If I try to boot from the XP hard-drive, it will boot, but it asks me to activate windows before proceeding. If I continue, I get the "activation window" with two images/icons(?) which are failing to load. Nothing else happens. The version of windows came with the original computer the hard-drive came from, so I'm not sure if I'm married to the broken computer (I hope not!). Is there anything I can do in order to boot into XP from the new computer?

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  • Why am I unable to access the network shares on my own computer?

    - by DoomStone
    I am having some problems with media center computer, with Windows 7 on it. The computers IP address is 192.168.1.13, and another computer can without any problem navigate to \\192.168.1.13, but the computer itself can not. Neither \\servername nor \\localhost. If I reboot the computer a couple of times, it will work again, but this is a big problem as my computer cleans my media center library on boot and there, if it can not access \\192.168.1.13, it will think that all the files have been removed and therefore delete them from the database. I really have no idea on where to start with this problem, but if anyone has tried this before and fixed it, I would be very happy, as it would save me from having to reinstall the whole system.

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  • Automatically make user local administrator on their computer through GPO?

    - by Grant
    In our AD 2003 domain each user gets local admin permissions on their computer. Everyone else can login with their domain account as normal user. Right now this means going to the desktop and manually adding the user as a local administrator. Is there any way to automate this process through logon scripts or GPOs? I have found ways to use a gpo to make everyone who logs in to a computer a local admin, but really only want to give it to the primary user (or in some cases users) of the computer. I've also seen methods that required adding a group for each computer...but really dont want to clutter AD like that. I do have a list mapping each user to each computer name. If it matters the desktops are a mix of xp and win7.

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  • Converting EBNF to BNF

    - by Vivin Paliath
    It's been a few years since my computer-language class and so I've forgotten the finer points of BNF's and EBNF's and I don't have a textbook next to me. Specifically, I've forgotten how to convert an EBNF into BNF. From what little I remember, I know that one of the main points is to convert { term } into <term> | <many-terms>. But I don't remember the other rules. I've tried to look this up online but I can only find links to either homework questions, or a small comment about converting terms with curly braces. I can't find an exhaustive list of rules that define the translation.

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