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  • Best ways to write a method that updates two objects in a multithreaded java environment?

    - by DanielHonig
    Suppose we have a class called AccountService that manages the state of accounts. AccountService is defined as interface AccountService{ public void debit(account); public void credit(account); public void transfer(Account account, Account account1); } Given this definition, what is the best way to implement transfer() so that you can guarantee that transfer is an atomic operation. I'm interested in answers that reference Java 1.4 code as well as answers that might use resources from java.util.concurrent in Java 5

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  • Losing a programmer, what steps to take?

    - by Zak
    One of the programmers on our team is leaving for greener pastures. We will be going from 6 to 5. What steps should we take to ensure our development process continues to run smoothly, potentially while integrating in new blood. We are currently working on a short release cycle with iterative development. Design - code - review. The person leaving was the most senior dev on the team, and would often give lots of feedback to the rest of the team, especially during the design phase.

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  • Is it faster to count down than it is to count up?

    - by Bob
    Our computer science teacher once said that for some reason it is more efficient to count down that count up. For example if you need to use a FOR loop and the loop index is not used somewhere (like printing a line of N * to the screen) I mean that code like this : for (i=N; i>=0; i--) putchar('*'); is better than: for (i=0; i<N; i++) putchar('*'); Is it really true? and if so does anyone know why?

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  • How to upload a file with JQueryMobile for an iphone/ipad?

    - by JD
    Hi, I have just started looking at JqueryMobile and want to know if the following is possible? I want to be able to select a file (similar to in html) and then show some sort of dialogue that allows me to browse to a "folder" and select the file. It would then be up to me to send some sort of AJAX command to upload it to the server (where I am using Asp.net MVC 2) Since I do not have access to an iPhone or iPad, I was told that I would only have access to the documents folder. JD

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  • Trying to packetize TCP with non-blocking IO is hard! Am I doing something wrong?

    - by Ricket
    Oh how I wish TCP was packet-based like UDP is! But alas, that's not the case, so I'm trying to implement my own packet layer. Here's the chain of events so far (ignoring writing packets) Oh, and my Packets are very simply structured: two unsigned bytes for length, and then byte[length] data. (I can't imagine if they were any more complex, I'd be up to my ears in if statements!) Server is in an infinite loop, accepting connections and adding them to a list of Connections. PacketGatherer (another thread) uses a Selector to figure out which Connection.SocketChannels are ready for reading. It loops over the results and tells each Connection to read(). Each Connection has a partial IncomingPacket and a list of Packets which have been fully read and are waiting to be processed. On read(): Tell the partial IncomingPacket to read more data. (IncomingPacket.readData below) If it's done reading (IncomingPacket.complete()), make a Packet from it and stick the Packet into the list waiting to be processed and then replace it with a new IncomingPacket. There are a couple problems with this. First, only one packet is being read at a time. If the IncomingPacket needs only one more byte, then only one byte is read this pass. This can of course be fixed with a loop but it starts to get sorta complicated and I wonder if there is a better overall way. Second, the logic in IncomingPacket is a little bit crazy, to be able to read the two bytes for the length and then read the actual data. Here is the code, boiled down for quick & easy reading: int readBytes; // number of total bytes read so far byte length1, length2; // each byte in an unsigned short int (see getLength()) public int getLength() { // will be inaccurate if readBytes < 2 return (int)(length1 << 8 | length2); } public void readData(SocketChannel c) { if (readBytes < 2) { // we don't yet know the length of the actual data ByteBuffer lengthBuffer = ByteBuffer.allocate(2 - readBytes); numBytesRead = c.read(lengthBuffer); if(readBytes == 0) { if(numBytesRead >= 1) length1 = lengthBuffer.get(); if(numBytesRead == 2) length2 = lengthBuffer.get(); } else if(readBytes == 1) { if(numBytesRead == 1) length2 = lengthBuffer.get(); } readBytes += numBytesRead; } if(readBytes >= 2) { // then we know we have the entire length variable // lazily-instantiate data buffers based on getLength() // read into data buffers, increment readBytes // (does not read more than the amount of this packet, so it does not // need to handle overflow into the next packet's data) } } public boolean complete() { return (readBytes > 2 && readBytes == getLength()+2); } Basically I need feedback on my code. Please suggest any improvements. Even overhauling my entire system would be okay, if you have suggestions for how better to implement the whole thing. Book recommendations are welcome too; I love books. I just get the feeling that something isn't quite right.

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  • Which way to store this data is effective?

    - by Tattat
    I am writing a game, which need a map, and I want to store the map. The first thing I can think of, is using a 2D-array. But the problem is what data should I store in the 2D-array. The player can tap different place to have different reaction. So, I am thinking store a 2D-array with objects, when player click some position, and I find it in the array, and use the object in that array to execute a cmd. But I have a concern that storing lots of object may use lots of memory. So, I am think storing char/int only. But it seems that not enough for me. I want to store the data like that: { Type:1 Color:Green } No matter what color is, if they are all type 1, the have same reactions in logic, but the visual effect is based on the color. So, it is not easy to store using a prue char/int data, unless I make something like this: 1-5 --> all type 1. 1=color green , 2=color red, 3 = color yellow.... ... 6-10 --> all type 2. 2 = color green, 2 = color red ... ... So, do you have any ideas on how to minimize the ram use, but also easy for me to read... ...thx

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  • Is there any reason for a blocking call to winsock send() function on Vista to return immediately ?

    - by ivymike
    Hi All, Is there any reason for a blocking call to winsock's send() function on Vista to return immediately ? It works with expected delay on XP and below. I'm wondering if this has got anything to do with auto-tuning feature of Vista. Code: char *pBuffer; // pointer to data int bytes; // total size int i = 0, j=0; while (i < bytes) { j = send(m_sock, pBuffer+i, bytes-i, 0); i+=j; } Thanks, Pavan

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  • How do I define a monadic function to work on a list in J?

    - by Gregory Higley
    Let's say I have the following J expression: # 3 ((|=0:)#]) 1+i.1000 This counts the number of numbers between 1 and 1000 that are evenly divisible by 3. (Now, before anyone points out that there's an easier way to do this, this question is about the syntax of J, and not mathematics.) Let's say I define a monadic function for this, as follows: f =: monad define # y ((|=0:)#]) 1+i.1000 ) This works great with a single argument, e.g., f 4 250 If I pass a list in, I get a length error: f 1 2 3 |length error: f Now, I completely understand why I get the length error. When you substitute the list 1 2 3 for the y argument of the monad, you get: # 1 2 3 ((|=0:)#]) 1+i.1000 If you know anything about J, it's pretty clear why the length error is occurring. So, I don't need an explanation of that. I want to define the function such that when I pass a list, it returns a list, e.g., f 1 2 3 1000 500 333 How can I either (a) redefine this function to take a list and return a list or (b) get the function to work on a list as-is without being redefined, perhaps using some adverb or other technique?

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  • Java Servlet says file does not exist

    - by Austin
    Hello World! I have developed a java servlet that monitors a folder on a network drive for new files then does some actions on them depending on what kind of file it is. It worked in Eclipse when Eclipse and Tomcat were running with each other, but now that I have deployed it onto a server(different machine), the servlet keeps logging that it cannot find the folder to be mapped. The exact same network drive is mapped, and the folder definitely exists. This problem only occurs when the servlet is run on the server, not on the development machine. Thanks! PS: It is a Windows Server 2003 Enterprise Server with Tomcat v6 installed.

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  • What are the benefits of `while(condition) { //work }` and `do { //work } while(condition)`?

    - by Shaharyar
    I found myself confronted with an interview question where the goal was to write a sorting algorithm that sorts an array of unsorted int values: int[] unsortedArray = { 9, 6, 3, 1, 5, 8, 4, 2, 7, 0 }; Now I googled and found out that there are so many sorting algorithms out there! Finally I could motivate myself to dig into Bubble Sort because it seemed pretty simple to start with. I read the sample code and came to a solution looking like this: static int[] BubbleSort(ref int[] array) { long lastItemLocation = array.Length - 1; int temp; bool swapped; do { swapped = false; for (int itemLocationCounter = 0; itemLocationCounter < lastItemLocation; itemLocationCounter++) { if (array[itemLocationCounter] > array[itemLocationCounter + 1]) { temp = array[itemLocationCounter]; array[itemLocationCounter] = array[itemLocationCounter + 1]; array[itemLocationCounter + 1] = temp; swapped = true; } } } while (swapped); return array; } I clearly see that this is a situation where the do { //work } while(cond) statement is a great help to be and prevents the use of another helper variable. But is this the only case that this is more useful or do you know any other application where this condition has been used?

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  • A good way to look back arbitrary number of items in the Array.Fold in F#

    - by tk
    In the folder function of the Array.Fold operation, i want to look back arbitrary number of items. The only way i can figure out is like this. let aFolder (dataArray, curIdx, result) (dataItem) = let N = numItemsToLookBack(result, dataItem) let recentNitems = dataArray.[curIdx - n .. curIdx - 1] let result = aCalc(result, dataItem, recentNitems ) dataArray, curIdx + 1, result myDataArray | Array.fold aFolder (myDataArray, 0, initResult) As you can see, I passed the whole dataArray and index to the folder function to get the "recentNitems". But this way allows the folder function to access not only preceding data, but also the following data. Is there a better (or more functional) way?

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  • How do I clear the text contents of a div in javascript?

    - by Ben
    I'm temporarily adding contents to a div,tempDiv, and adding that to a link which is appended to a div, #contentHere, that's displayed. I need to clear the contents of tempDiv so that the links aren't appended to each other, creating a string of urls that don't link to anywhere. $(document).ready(function(){ $.getJSON("data.php", function(data){ for(i = 0; i < 5; i++){ $("#tempDiv").append(data.justIn[i].dataLink+ ' '); $("#contentHere").append("<a href=\"#tempDiv\">Click to go to the div link</a>"); //I need to clear the contents of tempDiv here } }); }); Solutions to clearing the temporary contents of the div as I go?

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  • how works applications which blocks web sites?

    - by noisy
    I know only one low-level way of blocking websites - hosts file. However, it is obvious that main stream programs has some other way of achieving this. I have an idea for new model of this kind of program, but without possibility of blocking sites it is useless :(

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  • How can I implement a splay tree that performs the zig operation last, not first?

    - by Jakob
    For my Algorithms & Data Structures class, I've been tasked with implementing a splay tree in Haskell. My algorithm for the splay operation is as follows: If the node to be splayed is the root, the unaltered tree is returned. If the node to be splayed is one level from the root, a zig operation is performed and the resulting tree is returned. If the node to be splayed is two or more levels from the root, a zig-zig or zig-zag operation is performed on the result of splaying the subtree starting at that node, and the resulting tree is returned. This is valid according to my teacher. However, the Wikipedia description of a splay tree says the zig step "will be done only as the last step in a splay operation" whereas in my algorithm it is the first step in a splay operation. I want to implement a splay tree that performs the zig operation last instead of first, but I'm not sure how it would best be done. It seems to me that such an algorithm would become more complex, seeing as how one needs to find the node to be splayed before it can be determined whether a zig operation should be performed or not. How can I implement this in Haskell (or some other functional language)?

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  • What does $this generally mean in PHP?

    - by xczzhh
    I am really new to PHP, so I am kind of confused seeing these different operators all day. Here is some code I came across when watching a video tutorail, I'd appreciate it if some could explain a little bit: function index() { $config = Array( 'protocol' => 'smtp', 'smtp_host' => 'ssl://smtp.googlemail.com', 'smtp_port' => 465, 'smtp_user' => '[email protected]', 'smtp_pass' =>'password', ); $this->load->library('email', $config); $this->email->set_newline("\r\n"); $this->email->from('[email protected]', 'Jerry'); $this->email->to('[email protected]'); $this->email->subject('this is an email test'); $this->email->message('this is test message!'); if($this->email->send()) { echo 'Your email was sent'; } else { show_error($this->email->print_debugger()); } } ...

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  • Dynamic added elements double effect after page transition

    - by Emil Moe
    I have added dynamic from jQuery in my code, but when I go back one page and return to the page where the 's are added and you press them, they somehow click twice now. I have tried with an alert('something'); when I click: $(document).on('click', '#products a', function() { alert('something'); } And it's shown twice when you return to the page. I have tried $('#products a').remove(); When you click the 'Back' button, because I thought all elements where added twice, but that made no difference. I don't have anything around these lines, maybe I need $(document).ready(); or something with pageinit?

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