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  • Handy Javascript array Extensions &ndash; distinct()

    - by Liam McLennan
    The following code adds a method to javascript arrays that returns a distinct list of values. Array.prototype.distinct = function() { var derivedArray = []; for (var i = 0; i < this.length; i += 1) { if (!derivedArray.contains(this[i])) { derivedArray.push(this[i]) } } return derivedArray; }; and to demonstrate: alert([1,1,1,2,2,22,3,4,5,6,7,5,4].distinct().join(',')); This produces 1,2,22,3,4,5,6,7

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  • Online ALTER TABLE in MySQL 5.6

    - by Marko Mäkelä
    This is the low-level view of data dictionary language (DDL) operations in the InnoDB storage engine in MySQL 5.6. John Russell gave a more high-level view in his blog post April 2012 Labs Release – Online DDL Improvements. MySQL before the InnoDB Plugin Traditionally, the MySQL storage engine interface has taken a minimalistic approach to data definition language. The only natively supported operations were CREATE TABLE, DROP TABLE and RENAME TABLE. Consider the following example: CREATE TABLE t(a INT); INSERT INTO t VALUES (1),(2),(3); CREATE INDEX a ON t(a); DROP TABLE t; The CREATE INDEX statement would be executed roughly as follows: CREATE TABLE temp(a INT, INDEX(a)); INSERT INTO temp SELECT * FROM t; RENAME TABLE t TO temp2; RENAME TABLE temp TO t; DROP TABLE temp2; You could imagine that the database could crash when copying all rows from the original table to the new one. For example, it could run out of file space. Then, on restart, InnoDB would roll back the huge INSERT transaction. To fix things a little, a hack was added to ha_innobase::write_row for committing the transaction every 10,000 rows. Still, it was frustrating that even a simple DROP INDEX would make the table unavailable for modifications for a long time. Fast Index Creation in the InnoDB Plugin of MySQL 5.1 MySQL 5.1 introduced a new interface for CREATE INDEX and DROP INDEX. The old table-copying approach can still be forced by SET old_alter_table=0. This interface is used in MySQL 5.5 and in the InnoDB Plugin for MySQL 5.1. Apart from the ability to do a quick DROP INDEX, the main advantage is that InnoDB will execute a merge-sort algorithm before inserting the index records into each index that is being created. This should speed up the insert into the secondary index B-trees and potentially result in a better B-tree fill factor. The 5.1 ALTER TABLE interface was not perfect. For example, DROP FOREIGN KEY still invoked the table copy. Renaming columns could conflict with InnoDB foreign key constraints. Combining ADD KEY and DROP KEY in ALTER TABLE was problematic and not atomic inside the storage engine. The ALTER TABLE interface in MySQL 5.6 The ALTER TABLE storage engine interface was completely rewritten in MySQL 5.6. Instead of introducing a method call for every conceivable operation, MySQL 5.6 introduced a handful of methods, and data structures that keep track of the requested changes. In MySQL 5.6, online ALTER TABLE operation can be requested by specifying LOCK=NONE. Also LOCK=SHARED and LOCK=EXCLUSIVE are available. The old-style table copying can be requested by ALGORITHM=COPY. That one will require at least LOCK=SHARED. From the InnoDB point of view, anything that is possible with LOCK=EXCLUSIVE is also possible with LOCK=SHARED. Most ALGORITHM=INPLACE operations inside InnoDB can be executed online (LOCK=NONE). InnoDB will always require an exclusive table lock in two phases of the operation. The execution phases are tied to a number of methods: handler::check_if_supported_inplace_alter Checks if the storage engine can perform all requested operations, and if so, what kind of locking is needed. handler::prepare_inplace_alter_table InnoDB uses this method to set up the data dictionary cache for upcoming CREATE INDEX operation. We need stubs for the new indexes, so that we can keep track of changes to the table during online index creation. Also, crash recovery would drop any indexes that were incomplete at the time of the crash. handler::inplace_alter_table In InnoDB, this method is used for creating secondary indexes or for rebuilding the table. This is the ‘main’ phase that can be executed online (with concurrent writes to the table). handler::commit_inplace_alter_table This is where the operation is committed or rolled back. Here, InnoDB would drop any indexes, rename any columns, drop or add foreign keys, and finalize a table rebuild or index creation. It would also discard any logs that were set up for online index creation or table rebuild. The prepare and commit phases require an exclusive lock, blocking all access to the table. If MySQL times out while upgrading the table meta-data lock for the commit phase, it will roll back the ALTER TABLE operation. In MySQL 5.6, data definition language operations are still not fully atomic, because the data dictionary is split. Part of it is inside InnoDB data dictionary tables. Part of the information is only available in the *.frm file, which is not covered by any crash recovery log. But, there is a single commit phase inside the storage engine. Online Secondary Index Creation It may occur that an index needs to be created on a new column to speed up queries. But, it may be unacceptable to block modifications on the table while creating the index. It turns out that it is conceptually not so hard to support online index creation. All we need is some more execution phases: Set up a stub for the index, for logging changes. Scan the table for index records. Sort the index records. Bulk load the index records. Apply the logged changes. Replace the stub with the actual index. Threads that modify the table will log the operations to the logs of each index that is being created. Errors, such as log overflow or uniqueness violations, will only be flagged by the ALTER TABLE thread. The log is conceptually similar to the InnoDB change buffer. The bulk load of index records will bypass record locking. We still generate redo log for writing the index pages. It would suffice to log page allocations only, and to flush the index pages from the buffer pool to the file system upon completion. Native ALTER TABLE Starting with MySQL 5.6, InnoDB supports most ALTER TABLE operations natively. The notable exceptions are changes to the column type, ADD FOREIGN KEY except when foreign_key_checks=0, and changes to tables that contain FULLTEXT indexes. The keyword ALGORITHM=INPLACE is somewhat misleading, because certain operations cannot be performed in-place. For example, changing the ROW_FORMAT of a table requires a rebuild. Online operation (LOCK=NONE) is not allowed in the following cases: when adding an AUTO_INCREMENT column, when the table contains FULLTEXT indexes or a hidden FTS_DOC_ID column, or when there are FOREIGN KEY constraints referring to the table, with ON…CASCADE or ON…SET NULL option. The FOREIGN KEY limitations are needed, because MySQL does not acquire meta-data locks on the child or parent tables when executing SQL statements. Theoretically, InnoDB could support operations like ADD COLUMN and DROP COLUMN in-place, by lazily converting the table to a newer format. This would require that the data dictionary keep multiple versions of the table definition. For simplicity, we will copy the entire table, even for DROP COLUMN. The bulk copying of the table will bypass record locking and undo logging. For facilitating online operation, a temporary log will be associated with the clustered index of table. Threads that modify the table will also write the changes to the log. When altering the table, we skip all records that have been marked for deletion. In this way, we can simply discard any undo log records that were not yet purged from the original table. Off-page columns, or BLOBs, are an important consideration. We suspend the purge of delete-marked records if it would free any off-page columns from the old table. This is because the BLOBs can be needed when applying changes from the log. We have special logging for handling the ROLLBACK of an INSERT that inserted new off-page columns. This is because the columns will be freed at rollback.

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  • scaling point sprites with distance

    - by Will
    How can you scale a point sprite by its distance from the camera? GLSL fragment shader: gl_PointSize = size / gl_Position.w; seems along the right tracks; for any given scene all sprites seem nicely scaled by distance. Is this correct? How do you compute the proper scaling for my vertex attribute size? I want each sprite to be scaled by the modelview matrix. I had played with arbitrary values and it seems that size is the radius in pixels at the camera, and is not in modelview scale. I've also tried: gl_Position = pMatrix * mvMatrix * vec4(vertex,1.0); vec4 v2 = pMatrix * mvMatrix * vec4(vertex.x,vertex.y+0.5*size,vertex.z,1.0); gl_PointSize = length(gl_Position.xyz-v2.xyz) * gl_Position.w; But this makes the sprites be bigger in the distance, rather than smaller:

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  • One dimensional cutting algorithm with minimum waste

    - by jm666
    Can anybody point me to some resources about "cutting algorithm"? The problem: have rods with length of L meters, e.g. 6 m need cut smaller pieces of different lengths, e.g. need: 4 x 1.2m 8 x 0,9m etc... (many other lengths and counts) How to determine the optimal cutting, what will produce the minimum wasted material? I'm capable write an perl program, but haven't any idea about the algorithm. (if here is already some CPAN module what can help, would be nice). Alternatively, if someone can point me to some "spreadsheet" solution, or to anything what helps. Ps: in addition, need care about the "cutting line width" too, whats means than from the 6m long rod is impossible to cut 6 x 1m, because the cutting itself takes "3mm" width, so it is possible cut only 5 x 1m and the last piece will be only 98.5 cm (1m minus 5 x 3mm cut-width) ;(.

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  • How to speed up SSH login using a public key and PuTTY?

    - by BarsMonster
    Hi! I am using PuTTY to log into my local server, but it takes about 1.5 seconds to log in (from the click on 'Connect' to working command prompt, most of time is spend on "Authenticating with public key..."). I know many see even slower speeds, but I would like to have not more than 0.1 sec. login time. I already set UseDNS=no, allowed only IPv4 in the PuTTY client, and reduced key length from 4k down to 1k. Any other suggestions to speed it up even further?

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  • Circle vs Edge collision detection / resolution

    - by topheman
    I made a javascript class Ball.js that handles physics interactions betweens balls as well as painting. In the v1.0, the ball vs ball collision detection and resolution is well handled. In the next version (v2), I'm trying to add edgeCollision handling. I'm having some problems, maybe you will be able to help me. All the v2 branch source code is on github repository : https://github.com/topheman/Ball.js/tree/v2 The v2 demos (where you can see the bug I will be talking about) : http://labs.topheman.com/Ball-v2/#help As you will see on the demo, I have two major problems that I'm having a really hard time to solve on Ball.js : method resolveEdgeCollision : bounce angle is inconsistent method checkEdgeCollision : if the ball's velocity (the length that it runs each frame) is higher than its diameter, eventually, it will pass through an edge, without triggering any collision Any Ideas ?...

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  • Logging in JSON Effect on Performance

    - by Pius
    I see more and more articles about logging in JSON. You can also find one on NodeJS blog. Why does everyone like it so much? I can only see more operations getting involved: A couple new objects being created. Stringifying objects, which either involves calculating string length or multiple string allocations. GCing all the crap that was created. Is there any test on performance when using JSON logging and regular string logging? Do people use JSON (for logging) in enterprise projects?

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  • Detect if square in grid is within a diamond shape

    - by myrkos
    So I have a game in which basically everything is a square inside a big grid. It's easy to check if a square is inside a box whose center is another square: *** x *o* --> x is not in o's square *** **x *o* --> x IS in o's square *** This can be done by simply subtracting the coordinates of o and x, then taking the largest coordinate of that and comparing it with the half side length. Now I want to do the same thing but check if x is in o's diamond, like so: * **x **o** --> x IS in o's diamond *** * What would be the best way to check if a square is in another square's surrounding diamond-shaped area, given the diamond's half width/height?

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  • Circle physics and collision using vectors

    - by Joe Hearty
    This is a problem I've been having, When making a set number of filled circles at random locations on a JPanel and applying a gravity (a negative change in the y), each of the circles collide. I want them to have collision detection and push in the opposite direction using vectors but I don't know how to apply that to my scenario could someone help? public void drawballs(Graphics g){ g.setColor (Color.white); //displays circles for(int i = 0; i<xlocationofcircles.length-1; i++){ g.fillOval( (int) xlocationofcircles[i], (int) (ylocationofcircles[i]) ,16 ,16 ); ylocationofcircles[i]+=.2; //gravity if(ylocationofcircles[i] > 550) //stops gravity at bottom of screen ylocationofcircles[i]-=.2; //Check distance between circles(i think..) float distance =(xlocationofcircles[i+1]-xlocationofcircles[i]) + (ylocationofcircles[i+1]-xlocationofcircles[i]); if( Math.sqrt(distance) <16) ...

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  • Missing return statement when using .charAt [migrated]

    - by Timothy Butters
    I need to write a code that returns the number of vowels in a word, I keep getting an error in my code asking for a missing return statement. Any solutions please? :3 import java.util.*; public class vowels { public static void main(String[] args) { Scanner input = new Scanner(System.in); System.out.println("Please type your name."); String name = input.nextLine(); System.out.println("Congratulations, your name has "+ countVowels(name) +" vowels."); } public static int countVowels(String str) { int count = 0; for (int i=0; i < str.length(); i++) { // char c = str.charAt(i); if (str.charAt(i) == 'a' || str.charAt(i) == 'e' || str.charAt(i) == 'o' || str.charAt(i) == 'i' || str.charAt(i) == 'u') count = count + 1; } } }

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  • Repeating keywords in inbound links

    - by JJ_Jason
    Hy. I have a service similar to bit.ly. The link generation method is similar but the site is not. A user uses my site just like the mentioned bit.ly, but i offer a differnet kind of service for which i would want to rank (on Google) for. If i were to generate links such as: mysite.com/my-keywords/1Asdf34 would it be considered spammy or black hat? The same for bit.ly would be: bit.ly/url-shortening-services/3k1dS4sd For bit.ly it would defeat the purpose, but url length in my case does not have to be short.

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  • Creating a 2D Line Branch (Part 2)

    - by Danran
    Yesterday i asked this question on how to create a 2D line branch; Creating a 2D Line Branch And thanks to the answered provided, i now have this nice looking main branch; *coloured to show the different segments in the final item. Now is the time now to branch things off as discussed in the article; http://drilian.com/2009/02/25/lightning-bolts/ Again however i am confused as to the meaning of the following pseudo code; splitEnd = Rotate(direction, randomSmallAngle)*lengthScale + midPoint; I'm unsure how to actually rotate this correctly. In all honesty i'm abit unsure what to-do completely at this part, "splitEnd" will be a Vector3, so whatever happens in the rotate function must then return some form of directional rotation which is then * by a scale to create length and then added to the midPoint. I'm not sure. If someone could explain what i'm meant to be doing in this part that would be really grateful.

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  • Recommended Reading for Polishing JavaScript coding style?

    - by wml653
    I've been coding in JavaScript for a while now and am fairly familiar with some of the more advanced coding features of the language (closures, self-executing functions, etc). So my question is, what advanced books/blogs/or anything else would be recommended to help tighten up my coding style? For example, recently I was coding something similar to: var x = ['a', 'b', 'c']; var exists = false; for(var i = 0; i < x.length; i++){ exists = x[i] === 'b' ? true : exists; } But found that the following condensed code would work better: var y = {'a':'', 'b':'', 'c':''}; var exists = 'b' in y; Both store the same value in 'exists', but the second is less common, but much cleaner. Any suggestions for where I should go to learn more tricks like this?

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  • Setting a leader from a sprite array

    - by Craig
    I'm looking to set a leader from an array of sprites, I keep on getting a NullReferenceException was unhandled error from within my main game class when calling the UpdateMouse Method. What have I dont wrong here? class MouseSprite { Random random = new Random(); private MouseSprite leader; public void UpdateBoundaryBox() { mouseBounds.X = (int)mousePosition.X - mouseTexture.Width / 2; mouseBounds.Y = (int)mousePosition.Y - mouseTexture.Height / 2; } public void UpdateMouse(Vector2 position, MouseSprite [] mice, int numberMice, int index) { Vector2 catPosition = position; int enemies = numberMice; this.alive = true; mice[random.Next(0, mice.Length)] = leader;

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  • What are some good, simple examples for queues?

    - by Michael Ekstrand
    I'm teaching CS2 (Java and data structures), and am having some difficulty coming up with good examples to use when teaching queues. The two major applications I use them for are multithreaded message passing (but MT programming is out of scope for the course), and BFS-style algorithms (and I won't be covering graphs until later in the term). I also want to avoid contrived examples. Most things that I think of, if I were actually going to solve them in a single-threaded fashion I would just use a list rather than a queue. I tend to only use queues when processing and discovery are interleaved (e.g. search), or in other special cases like length-limited buffers (e.g. maintaining last N items). To the extent practical, I am trying to teach my students good ways to actually do things in real programs, not just toys to show off a feature. Any suggestions of good, simple algorithms or applications of queues that I can use as examples but that require a minimum of other prior knowledge?

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  • Key Promoter for NetBeans

    - by Geertjan
    Whenever a menu item or toolbar button is clicked, it would be handy if NetBeans were to tell you 'hey, did you know, you can actually do this via the following keyboard shortcut', if a keyboard shortcut exists for the invoked action. After all, ultimately, a lot of developers would like to do everything with the keyboard and a key promoter feature of this kind is a helpful tool in learning the keyboard shortcuts related to the menu items and toolbar buttons you're clicking with your mouse. Above, you see the balloon message that appears for each menu item and toolbar button that you click and, below, you can see a list of all the actions that have been logged in the Notifications window. That happens automatically when an action is invoked (assuming the plugin described in this blog entry is installed), showing the display name of the action, together with the keyboard shortcut, which is presented as a hyperlink which, when clicked, re-invokes the action (which might not always be relevant, especially for context-sensitive actions, though for others it is quite useful, e.g., reopen the New Project wizard). And here's all the code. Notice that I'm hooking into the 'uigestures' functionality, which was suggested by Tim Boudreau, and I have added my own handler, which was suggested by Jaroslav Tulach, which gets a specific parameter from each new log entry handled by the 'org.netbeans.ui.actions' logger, makes sure that the parameter actually is an action, and then gets the relevant info from the action, if the relevant info exists: @OnShowingpublic class Startable implements Runnable {    @Override    public void run() {        Logger logger = Logger.getLogger("org.netbeans.ui.actions");        logger.addHandler(new StreamHandler() {            @Override            public void publish(LogRecord record) {                Object[] parameters = record.getParameters();                if (parameters[2] instanceof Action) {                    Action a = (Action) parameters[2];                    JMenuItem menu = new JMenuItem();                    Mnemonics.setLocalizedText(                            menu,                             a.getValue(Action.NAME).toString());                    String name = menu.getText();                    if (a.getValue(Action.ACCELERATOR_KEY) != null) {                        String accelerator = a.getValue(Action.ACCELERATOR_KEY).toString();                        NotificationDisplayer.getDefault().notify(                                name,                                 new ImageIcon("/org/nb/kp/car.png"),                                 accelerator,                                 new ActionListener() {                            @Override                            public void actionPerformed(ActionEvent e) {                                a.actionPerformed(e);                            }                        });                    }                }            }        });    }} Indeed, inspired by the Key Promoter in IntelliJ IDEA. Interested in trying it out? If there's interest in it, I'll put it in the NetBeans Plugin Portal.

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  • How can I correct the paper size (A4) for Canon i560 printer for 12.04?

    - by Peter
    How can I correct the paper size (A4) for Canon i560 printer for 12.04? Canon i560-Paper size error-with printer driver for Ubuntu 12.04 Precise Pangolin offers the same problem, but the answers are not very helpful/elegant to me. Especially the second is far too imprecise and the dimensions for A4 suggested there do not seem to be correct as they do not match with any other (and correctly working) A-Size dimensions. My i560.ppd has for A4 a length of [842] which is then the width for A3 throughout the ppd-file. A3 printouts are fine (So just the way it should be). A4 are not. Cannot figure out why.

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  • Form Validation, Dependant Drop Downs, Data Level Security in OWS for DotNetNuke - 5 Videos

    In this tutorial we demonstrate some very advanced techniques for building a car parts application in Open Web Studio. Throughout the tutorial we cover form input, validation, how to use dependant drop down lists, populating checkbox lists and introduce a new concept of data level security. Data level security allows you to control which data a user can access within a module. The videos contain: Video 1 - How to Setup Form Validation Video 2 - Car Parts Application, Assigning Security Roles into a Global Session Variable Video 3 - How to Build the Categories Module with Data Level Security Video 4 - How to Build the SubCategories Module and Use SubQuery Video 5 - How to Build the Car Parts List Module Total Time Length: 44min 19secsDid you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • Using .add() on the same widget more than once

    - by Dillon Gilmore
    I asked this question on Reddit and was directed here. http://www.reddit.com/r/Ubuntu/comments/vhadl/quickly_dynamic_ui/ Unfortunately I am having the same issue and the problems seems that you can only use .add() on a widget once. So here is my code, self.ui.labels = [] for titles in entries: label = Gtk.Label() self.ui.labels.append(label) self.ui.viewport1.add(self.ui.labels[-1]) self.ui.paned1.show_all() Now, for fun I decided "What would happen if I just manually did..." self.ui.viewport1.add(Gtk.Label()) self.ui.viewport1.add(Gtk.Button()) self.ui.viewport1.add(Gtk.Entry()) For my first code snippet I get this error, Gtk-CRITICAL **: gtk_viewport_add: assertion gtk_bin_get_child (bin) == NULL' failed The error happens an unknown amount of times because the list entries can vary in length, but for my second code snippet it happens exactly twice. This means that when I viewport1.add() it works the first time, but all adds after that receive the error above. So my question, is there a way in python to use .add() on the same widget more than once?

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  • Speed up ssh login using public key down to 0.1sec

    - by BarsMonster
    Hi! I am using Putty to login to my local server, but it takes about 1.5 seconds to login (from the click on 'connect' to working command prompt, most of time is spend on "Authenticating with public key..."). I know many see even slower speeds, but I would like to have not more than 0.1 login time. I already set UseDNS=no and allowed only IPv4 in putty client and reduced key length from 4k down to 1k. Any other suggestions to speed it further?

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  • career change : non-functional to test automation

    - by centennial
    I started my Career as core-Java developer 6 years ago and stayed as developer for 6-7 month and then moved to performance testing (actualy pushed into this for short term and later I started liking it). I have done all sort of non-functional testing like performance, load, stress, soak, compatibility, failover etc on many performance test tools accross many industries. I was doing contracting all these years which means I kept moving to new projects after every 3-6 months. Now personal situation has been changed, married man now so looking for something long term. Performance testing generally comes at the end of the development life cycle hence very short term contracts so I was wondering if I can move into functional/test automation side I can earn myself good length of contract. I had some exposure of QTP but I am sure to learn all other tools very quickly as I am quite good in programming and concept of testing. in short I want to move into functional test automation to get long term contract without leaving my love for programming . any thoughts please ?

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  • Bubble shooter search alghoritm

    - by Fofole
    So I have a Matrix of NxM. At a given position (for ex. [2][5]) I have a value which represents a color. If there is nothing at that point the value is -1. What I need to do is after I add a new point, to check all his neighbours with the same color value and if there are more than 2, set them all to -1. If what I said doesn't make sense what I'm trying to do is an alghoritm which I use to destroy all the same color bubbles from my screen, where the bubbles are memorized in a matrix where -1 means no bubble and {0,1,2,...} represent that there is a bubble with a specific color. This is what I tried and failed: public class Testing { static private int[][] gameMatrix= {{3, 3, 4, 1, 1, 2, 2, 2, 0, 0}, {1, 4, 1, 4, 2, 2, 1, 3, 0, 0}, {2, 2, 4, 4, 3, 1, 2, 4, 0, 0}, {0, 1, 2, 3, 4, 1, 0, 0, 0, 0}, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, }; static int Rows=6; static int Cols=10; static int count; static boolean[][] visited=new boolean[15][15]; static int NOCOLOR = -1; static int color = 1; public static void dfs(int r, int c, int color, boolean set) { for(int dr = -1; dr <= 1; dr++) for(int dc = -1; dc <= 1; dc++) if(!(dr == 0 && dc == 0) && ok(r+dr, c+dc)) { int nr = r+dr; int nc = c+dc; // if it is the same color and we haven't visited this location before if(gameMatrix[nr][nc] == color && !visited[nr][nc]) { visited[nr][nc] = true; count++; dfs(nr, nc, color, set); if(set) { gameMatrix[nr][nc] = NOCOLOR; } } } } static boolean ok(int r, int c) { return r >= 0 && r < Rows && c >= 0 && c < Cols; } static void showMatrix(){ for(int i = 0; i < gameMatrix.length; i++) { System.out.print("["); for(int j = 0; j < gameMatrix[0].length; j++) { System.out.print(" " + gameMatrix[i][j]); } System.out.println(" ]"); } System.out.println(); } static void putValue(int value,int row,int col){ gameMatrix[row][col]=value; } public static void main(String[] args){ System.out.println("Initial Matrix:"); putValue(1, 4, 1); putValue(1, 5, 1); showMatrix(); for(int n = 0; n < 15; n++) for(int m = 0; m < 15; m++) visited[n][m] = false; //reset count count = 0; //dfs(bubbles.get(i).getRow(), bubbles.get(i).getCol(), color, false); // get the contiguous count dfs(5,1,color,false); //if there are more than 2 set the color to NOCOLOR for(int n = 0; n < 15; n++) for(int m = 0; m < 15; m++) visited[n][m] = false; if(count > 2) { //dfs(bubbles.get(i).getRow(), bubbles.get(i).getCol(), color, true); dfs(5,1,color,true); } System.out.println("Matrix after dfs:"); showMatrix(); } }

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  • OutOfBounds Exception when creating a PolygonShape using jbox2d

    - by B3nGr33ni3r
    So here's the deal, i'm parsing a file that contains the vertices for a polygon, that i want to create in box2d. I create a new PolygonShape() and then call .set() giving it a defined array of Vec, and that defined array's .length property. I expected this to work, since the documentation for jbox2d says this method takes a Vec array, and the count of Vec objects in that array. However, it errors out, and it seems to be unrelated to my code. The error i get is Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 8 at org.jbox2d.collision.shapes.PolygonShape.set(PolygonShape.java:174) and, upon looking at that line in the jbox2d svn repository, i still cannot figure out the issue. Any help is appreciated!

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  • Collaborative Whiteboard using WebSocket in GlassFish 4 - Text/JSON and Binary/ArrayBuffer Data Transfer (TOTD #189)

    - by arungupta
    This blog has published a few blogs on using JSR 356 Reference Implementation (Tyrus) as its integrated in GlassFish 4 promoted builds. TOTD #183: Getting Started with WebSocket in GlassFish TOTD #184: Logging WebSocket Frames using Chrome Developer Tools, Net-internals and Wireshark TOTD #185: Processing Text and Binary (Blob, ArrayBuffer, ArrayBufferView) Payload in WebSocket TOTD #186: Custom Text and Binary Payloads using WebSocket One of the typical usecase for WebSocket is online collaborative games. This Tip Of The Day (TOTD) explains a sample that can be used to build such games easily. The application is a collaborative whiteboard where different shapes can be drawn in multiple colors. The shapes drawn on one browser are automatically drawn on all other peer browsers that are connected to the same endpoint. The shape, color, and coordinates of the image are transfered using a JSON structure. A browser may opt-out of sharing the figures. Alternatively any browser can send a snapshot of their existing whiteboard to all other browsers. Take a look at this video to understand how the application work and the underlying code. The complete sample code can be downloaded here. The code behind the application is also explained below. The web page (index.jsp) has a HTML5 Canvas as shown: <canvas id="myCanvas" width="150" height="150" style="border:1px solid #000000;"></canvas> And some radio buttons to choose the color and shape. By default, the shape, color, and coordinates of any figure drawn on the canvas are put in a JSON structure and sent as a message to the WebSocket endpoint. The JSON structure looks like: { "shape": "square", "color": "#FF0000", "coords": { "x": 31.59999942779541, "y": 49.91999053955078 }} The endpoint definition looks like: @WebSocketEndpoint(value = "websocket",encoders = {FigureDecoderEncoder.class},decoders = {FigureDecoderEncoder.class})public class Whiteboard { As you can see, the endpoint has decoder and encoder registered that decodes JSON to a Figure (a POJO class) and vice versa respectively. The decode method looks like: public Figure decode(String string) throws DecodeException { try { JSONObject jsonObject = new JSONObject(string); return new Figure(jsonObject); } catch (JSONException ex) { throw new DecodeException("Error parsing JSON", ex.getMessage(), ex.fillInStackTrace()); }} And the encode method looks like: public String encode(Figure figure) throws EncodeException { return figure.getJson().toString();} FigureDecoderEncoder implements both decoder and encoder functionality but thats purely for convenience. But the recommended design pattern is to keep them in separate classes. In certain cases, you may even need only one of them. On the client-side, the Canvas is initialized as: var canvas = document.getElementById("myCanvas");var context = canvas.getContext("2d");canvas.addEventListener("click", defineImage, false); The defineImage method constructs the JSON structure as shown above and sends it to the endpoint using websocket.send(). An instant snapshot of the canvas is sent using binary transfer with WebSocket. The WebSocket is initialized as: var wsUri = "ws://localhost:8080/whiteboard/websocket";var websocket = new WebSocket(wsUri);websocket.binaryType = "arraybuffer"; The important part is to set the binaryType property of WebSocket to arraybuffer. This ensures that any binary transfers using WebSocket are done using ArrayBuffer as the default type seem to be blob. The actual binary data transfer is done using the following: var image = context.getImageData(0, 0, canvas.width, canvas.height);var buffer = new ArrayBuffer(image.data.length);var bytes = new Uint8Array(buffer);for (var i=0; i<bytes.length; i++) { bytes[i] = image.data[i];}websocket.send(bytes); This comprehensive sample shows the following features of JSR 356 API: Annotation-driven endpoints Send/receive text and binary payload in WebSocket Encoders/decoders for custom text payload In addition, it also shows how images can be captured and drawn using HTML5 Canvas in a JSP. How could this be turned in to an online game ? Imagine drawing a Tic-tac-toe board on the canvas with two players playing and others watching. Then you can build access rights and controls within the application itself. Instead of sending a snapshot of the canvas on demand, a new peer joining the game could be automatically transferred the current state as well. Do you want to build this game ? I built a similar game a few years ago. Do somebody want to rewrite the game using WebSocket APIs ? :-) Many thanks to Jitu and Akshay for helping through the WebSocket internals! Here are some references for you: JSR 356: Java API for WebSocket - Specification (Early Draft) and Implementation (already integrated in GlassFish 4 promoted builds) Subsequent blogs will discuss the following topics (not necessary in that order) ... Error handling Interface-driven WebSocket endpoint Java client API Client and Server configuration Security Subprotocols Extensions Other topics from the API

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  • Unit testing a text index

    - by jplot
    Consider a text index such as a suffix tree or a suffix array supporting Count queries (number of occurrences of a pattern) and Locate queries (the positions of all the occurrences of a pattern) over a given text. How would you go about unit testing such a class ? What I have in mind is to generate a big random string then extract a random substring from this big string and compare the results of both queries with naive implementations (such as string::find). Another idea I have is to find the most frequent substring of length l appearing in the original string (using perhaps a naive method) and use these substrings for testing the index. This isn't the best way, so what would be a good design of the unit tests for a text index ? In case it matters, this is in C++ using google test.

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