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  • Correct way to add objects to an ArrayList

    - by ninjasense
    I am trying to add an object to an arraylist but when I view the results of the array list, it keeps adding the same object over and over to the arraylist. I was wondering what the correct way to implement this would be. public static ArrayList<Person> parsePeople(String responseData) { ArrayList<Person> People = new ArrayList<Person>(); try { JSONArray jsonPeople = new JSONArray(responseData); if (!jsonPeople.isNull(0)) { for (int i = 0; i < jsonPeople.length(); i++) { Person.add(new Person(jsonPeople.getJSONObject(i))); } } } catch (JSONException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (Exception e) { } return People; } I have double checked my JSONArray data and made sure they are not duplicates. It seems to keep adding the first object over and over.

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  • FacesMessages and rich:effect?

    - by user331747
    I'd like to be able to make an Ajax call using JSF/Seam/RichFaces and have the page update with the relevant h:messages component. That works with no problem. I'm able to perform the appropriate reRender. However, I'd also like to be able to make use of rich:effect to make it a bit prettier. Ideally, I'd like to be able to have the messages fade in and then disappear when the user clicks on them. However, I've been unable to get this working thus far. Has anyone gotten such a scenario working? Does anyone who knows JSF/Seam a bit better than me have any good advice? Thanks in advance!

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  • efficiently trimming postgresql tables

    - by agilefall
    I have about 10 tables with over 2 million records and one with 30 million. I would like to efficiently remove older data from each of these tables. My general algorithm is: create a temp table for each large table and populate it with newer data truncate the original tables copy tmp data back to original tables using: "insert into originaltable (select * from tmp_table)" However, the last step of copying the data back is taking longer than I'd like. I thought about deleting the original tables and making the temp tables "permanent", but I lose constraint/foreign key info. If I delete from the tables directly, it takes much longer. Given that I need to preserve all foreign keys and constraints, are there any faster ways of removing the older data? Thanks.

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  • How can I make Emacs start-up faster?

    - by Colin
    I use Emacs v. 22 (the console version, either remotely with PuTTY or locally with Konsole) as my primary text editor on Linux. It takes a while to load up each time I start it though, probably almost a second, although I never timed it. I tend to open and close Emacs a lot, because I'm more comfortable using the Bash command-line for file/directory manipulation and compiling. How can I speed up the start-up time?

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  • How to convince a colleague that code duplication is bad?

    - by vitaut
    A colleague of mine was implementing a new feature in a project we work on together and he did it by taking a file containing the implementation of a similar feature from the same project, creating a copy of it renaming all the global declarations and slightly modifying the implementation. So we ended up with two large files that are almost identical apart from renaming. I tried to explain that it makes our project more difficult to maintain but he doesn't want to change anything saying that it is easier for him to program in such way and that there is no reason to fix the code if it "ain't broke". How can I convince him that such code duplication is a bad thing? It is related to this questions, but I am more interested in the answers targeted to a technical person (another programmer), for example a reference to an authoritative source like a book would be great. I have already tried simple arguments and haven't succeeded.

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  • when to use StringBuilder in java

    - by kostja
    It is supposed to be generally preferable to use a StringBuilder for String concatenation in Java. Is it always the case? What i mean is : Is the overhead of creating a StringBuilder object, calling the append() method and finally toString() smaller then concatenating existing Strings with + for 2 Strings already or is it only advisable for more Strings? If there is such a threshold, what does it depend on (the String length i suppose, but in which way)? And finally - would you trade the readability and conciseness of the + concatenation for the performance of the StringBuilder in smaller cases like 2, 3, 4 Strings?

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  • What is the most efficient algorithm for reversing a String in Java?

    - by Hultner
    I am wondering which way to reverse a string in Java that is most efficient. Should I use some sort of xor method? The easy way would be to put all the chars in a stack and put them back into a string again but I doubt that's a very efficient way to do it. And please do not tell me to use some built in function in Java. I am interested in learning how to do it not to use an efficient function but not knowing why it's efficient or how it's built up.

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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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  • [perl] Efficient processing of large text

    - by jesper
    I have text file that contains over one million urls. I have to process this file in order to assign urls to groups, based on host address: { 'http://www.ex1.com' = ['http://www.ex1.com/...', 'http://www.ex1.com/...', ...], 'http://www.ex2.com' = ['http://www.ex2.com/...', 'http://www.ex2.com/...', ...] } My current basic solution takes about 600mb of RAM to do this (size of file is about 300mb). Could You provide some more efficient ways? My current solution simply reads line by line, extracts host address by regex and put url into hash.

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  • Question About Eclipse Java Debugger Conditional Breakpoints Inefficiency

    - by Personman
    I just set a conditional breakpoint in Eclipse's debugger with a mildly inefficient condition by breakpoint standards - checking whether a HashMap's value list (8 elements) contains Double.NaN. This resulted in an extremely noticeable slowdown in performance - after about five minutes, I gave up. Then I copy pasted the condition into an if statement at the exact same line, put a noop in the if, and set a normal breakpoint there. That breakpoint was reached in the expected 20-30 seconds. Is there something special that conditional breakpoints do that is different from this, or is Eclipse's implementation just kinda stupid? It seems like they could fairly easily just do exactly the same thing behind the scenes.

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  • What is the most efficient way to read many bytes from SQL Server using SqlDataReader (C#)

    - by eccentric
    Hi everybody! What is the most efficient way to read bytes (8-16 K) from SQL Server using SqlDataReader. It seems I know 2 ways: byte[] buffer = new byte[4096]; MemoryStream stream = new MemoryStream(); long l, dataOffset = 0; while ((l = reader.GetBytes(columnIndex, dataOffset, buffer, 0, buffer.Length)) > 0) { stream.Write(buffer, 0, buffer.Length); dataOffset += l; } and reader.GetSqlBinary(columnIndex).Value The data type is IMAGE

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  • Big O Complexity of a method

    - by timeNomad
    I have this method: public static int what(String str, char start, char end) { int count=0; for(int i=0;i<str.length(); i++) { if(str.charAt(i) == start) { for(int j=i+1;j<str.length(); j++) { if(str.charAt(j) == end) count++; } } } return count; } What I need to find is: 1) What is it doing? Answer: counting the total number of end occurrences after EACH (or is it? Not specified in the assignment, point 3 depends on this) start. 2) What is its complexity? Answer: the first loops iterates over the string completely, so it's at least O(n), the second loop executes only if start char is found and even then partially (index at which start was found + 1). Although, big O is all about worst case no? So in the worst case, start is the 1st char & the inner iteration iterates over the string n-1 times, the -1 is a constant so it's n. But, the inner loop won't be executed every outer iteration pass, statistically, but since big O is about worst case, is it correct to say the complexity of it is O(n^2)? Ignoring any constants and the fact that in 99.99% of times the inner loop won't execute every outer loop pass. 3) Rewrite it so that complexity is lower. What I'm not sure of is whether start occurs at most once or more, if once at most, then method can be rewritten using one loop (having a flag indicating whether start has been encountered and from there on incrementing count at each end occurrence), yielding a complexity of O(n). In case though, that start can appear multiple times, which most likely it is, because assignment is of a Java course and I don't think they would make such ambiguity. Solving, in this case, is not possible using one loop... WAIT! Yes it is..! Just have a variable, say, inc to be incremented each time start is encountered & used to increment count each time end is encountered after the 1st start was found: inc = 0, count = 0 if (current char == start) inc++ if (inc > 0 && current char == end) count += inc This would also yield a complexity of O(n)? Because there is only 1 loop. Yes I realize I wrote a lot hehe, but what I also realized is that I understand a lot better by forming my thoughts into words...

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  • Getting Factors of a Number

    - by Dave
    Hi Problem: I'm trying to refactor this algorithm to make it faster. What would be the first refactoring here for speed? public int GetHowManyFactors(int numberToCheck) { // we know 1 is a factor and the numberToCheck int factorCount = 2; // start from 2 as we know 1 is a factor, and less than as numberToCheck is a factor for (int i = 2; i < numberToCheck; i++) { if (numberToCheck % i == 0) factorCount++; } return factorCount; }

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  • MySQL: Return grouped fields where the group is not empty, effeciently

    - by Ryan Badour
    In one statement I'm trying to group rows of one table by joining to another table. I want to only get grouped rows where their grouped result is not empty. Ex. Items and Categories SELECT Category.id FROM Item, Category WHERE Category.id = Item.categoryId GROUP BY Category.id HAVING COUNT(Item.id) > 0 The above query gives me the results that I want but this is slow, since it has to count all the rows grouped by Category.id. What's a more effecient way? I was trying to do a Group By LIMIT to only retrieve one row per group. But my attempts failed horribly. Any idea how I can do this? Thanks

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  • How to pass a file (read from Java) most effectively to a native method?

    - by soc
    Hi, I have approx. 30000 files (1MB each) which I want to put into a native method, which requires just an byte array and the size of it as arguments. I looked through some examples and benchmarks (like http://nadeausoftware.com/articles/2008/02/java_tip_how_read_files_quickly) but all of them do some other fancy things. Basically I don't care about the contents of the file, I don't want to access something in that file or the byte array or do anything else with it. I just want to put a file into a native method which accepts an byte array as fast as possible. At the moment I'm using RandomAccessFile, but that's horribly slow (10MB/s). Is there anything like byte[] readTheWholeFile(File file){ ... } which I could put into native void fancyCMethod(readTheWholeFile(myFile), myFile.length()) What would you suggest?

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  • Log4J - Speed of resolving class/method/line references

    - by Jeach
    Does log4J still gather the class, method and line numbers by generating exceptions and inspecting the stack trace? Or has Java been optimized since Sun included their own logging framework. If not, why has there not been any optimizations made since. What is the main challenges in obtaining class, method and line numbers quickly and efficiently? Although I hate annotations and try to avoid them, has log4J not made use of this, such as: @log4j-class MyClass @log4j-method currentMethodOne At least this would avoid some companies bad habit of repeatedly writing/copying the method name as the first part of their logging message (which is seriously annoying). Thanks, Jeach!

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  • How to make this JavaScript much faster?

    - by Ralph
    Still trying to answer this question, and I think I finally found a solution, but it runs too slow. var $div = $('<div>') .css({ 'border': '1px solid red', 'position': 'absolute', 'z-index': '65535' }) .appendTo('body'); $('body *').live('mousemove', function(e) { var topElement = null; $('body *').each(function() { if(this == $div[0]) return true; var $elem = $(this); var pos = $elem.offset(); var width = $elem.width(); var height = $elem.height(); if(e.pageX > pos.left && e.pageY > pos.top && e.pageX < (pos.left + width) && e.pageY < (pos.top + height)) { var zIndex = document.defaultView.getComputedStyle(this, null).getPropertyValue('z-index'); if(zIndex == 'auto') zIndex = $elem.parents().length; if(topElement == null || zIndex > topElement.zIndex) { topElement = { 'node': $elem, 'zIndex': zIndex }; } } }); if(topElement != null ) { var $elem = topElement.node; $div.offset($elem.offset()).width($elem.width()).height($elem.height()); } }); It basically loops through all the elements on the page and finds the top-most element beneath the cursor. Is there maybe some way I could use a quad-tree or something and segment the page so the loop runs faster?

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  • Efficiently store last X items in an MySQL Database

    - by Saif Bechan
    I want to store the last 3 items in an MySQL database in an efficient way. So when the 4th item is stored the first should be deleted. The way I do this not is first run a query getting the items. Than check what I should do then insert/delete. There has to be a better way to do this. Any suggestions?

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  • Fastest file reading in C.

    - by Jay
    Right now I am using fread() to read a file, but in other language fread() is inefficient i'v been told. Is this the same in C? If so, how would faster file reading be done?

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  • C++ - Efficient way to iterate over the contents of a vector?

    - by Francisco P.
    Hello, everyone! I am implementing a text-based version of Scrabble for a college project. I have a vector containing around 400K strings (my dictionary), and, at some point in every turn, I'm going to have to check if any word in the dictionary can be formed with the pieces in the player's hand. My only solution to this is iterating through the string, one by one, and using a sub-routine I have to check if the string in question can be formed from the player's pieces. I'll implement a quickfail checking if the user has any vowels, but it'll still be woefully inefficient. Any suggestions? Thanks for your time!

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  • Fastest method in merging of the two: dicts vs lists

    - by tipu
    I'm doing some indexing and memory is sufficient but CPU isn't. So I have one huge dictionary and then a smaller dictionary I'm merging into the bigger one: big_dict = {"the" : {"1" : 1, "2" : 1, "3" : 1, "4" : 1, "5" : 1}} smaller_dict = {"the" : {"6" : 1, "7" : 1}} #after merging resulting_dict = {"the" : {"1" : 1, "2" : 1, "3" : 1, "4" : 1, "5" : 1, "6" : 1, "7" : 1}} My question is for the values in both dicts, should I use a dict (as displayed above) or list (as displayed below) when my priority is to use as much memory as possible to gain the most out of my CPU? For clarification, using a list would look like: big_dict = {"the" : [1, 2, 3, 4, 5]} smaller_dict = {"the" : [6,7]} #after merging resulting_dict = {"the" : [1, 2, 3, 4, 5, 6, 7]} Side note: The reason I'm using a dict nested into a dict rather than a set nested in a dict is because JSON won't let me do json.dumps because a set isn't key/value pairs, it's (as far as the JSON library is concerned) {"a", "series", "of", "keys"} Also, after choosing between using dict to a list, how would I go about implementing the most efficient, in terms of CPU, method of merging them? I appreciate the help.

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  • What's the most efficient way to combine two List(Of String)?

    - by Jason Towne
    Let's say I've got: Dim los1 as New List(Of String) los1.Add("Some value") Dim los2 as New List(Of String) los2.Add("More values") What would be the most efficient way to combine the two into a single List(Of String)? Edit: While I'm loving the solutions everyone has provided so far, I probably should also mention I'm stuck using the .NET 2.0 framework. Any other suggestions?

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