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  • Need help extrapolating Java code

    - by Berlioz
    If anyone familiar with Rebecca Wirfs-Brock, she has a piece of Java code found in her book titled, Object Design: Roles, Responsibilities, and Collaborations. Here is the quote Applying Double Dispatch to a Specific Problem To implement the game Rock, Paper, Scissors we need to write code that determines whether one object “beats” another. The game has nine possible outcomes based on the three kinds of objects. The number of interactions is the cross product of the kinds of objects. Case or switch statements are often governed by the type of data that is being operated on. The object-oriented language equivalent is to base its actions on the class of some other object. In Java, it looks like this Here is the piece of Java code on page 16 ' import java.util.*; import java.lang.*; public class Rock { public static void main(String args[]) { } public static boolean beats(GameObject object) { if (object.getClass.getName().equals("Rock")) { result = false; } else if (object.getClass.getName().equals("Paper")) { result = false; } else if(object.getClass.getName().equals("Scissors")) { result = true; } return result; } }' ===This is not a very good solution. First, the receiver needs to know too much about the argument. Second, there is one of these nested conditional statements in each of the three classes. If new kinds of objects could be added to the game, each of the three classes would have to be modified. Can anyone share with me how to get this "less than optimal" piece of code to work in order to see it 'working'. She proceeds to demonstrate a better way, but I will spare you. Thanks

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  • query sql database for specific value in vb.net

    - by user2952298
    I am trying to convert VBA code to vb.net, im having trouble trying to search the database for a specific value around an if statement. any suggestions would be greatly appriciated. thedatabase is called confirmation, type is the column and email is the value im looking for. could datasets work? Function SendEmails() As Boolean Dim objOutlook As Outlook.Application Dim objOutlookMsg As Outlook.MailItem Dim objOutlookRecip As Outlook.Recipient Dim objOutlookAttach As Outlook.Attachment Dim intResponse As Integer Dim confirmation As New ADODB.Recordset Dim details As New ADODB.Recordset On Error GoTo Err_Execute Dim MyConnObj As New ADODB.Connection Dim cn As New ADODB.Connection() MyConnObj.Open( _ "Provider = sqloledb;" & _ "Server=myserver;" & _ "Database=Email_Text;" & _ "User Id=bla;" & _ "Password=bla;") confirmation.Open("Confirmation_list", MyConnObj) details.Open("MessagesToSend", MyConnObj) If details.EOF = False Then confirmation.MoveFirst() Do While Not confirmation.EOF If confirmation![Type] = "Email" Then ' Create the Outlook session. objOutlook = CreateObject("Outlook.Application") ' Create the message. End IF

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  • Strange results about C++11 memory model (Relaxed ordering)

    - by Dancing_bunny
    I was testing the example in the memory model of the Anthony Williams's book "C++ Concurrency" #include<atomic> #include<thread> #include<cassert> std::atomic_bool x,y; std::atomic_int z; void write_x_then_y() { x.store(true, std::memory_order_relaxed); y.store(true, std::memory_order_relaxed); } void read_y_then_x() { while(!y.load(std::memory_order_relaxed)); if(x.load(std::memory_order_relaxed)) { ++z; } } int main() { x = false; y = false; z = 0; std::thread a(write_x_then_y); std::thread b(read_y_then_x); a.join(); b.join(); assert(z.load()!=0); } According to the explanation, relaxed operations on difference variables (here x and y) can be freely reordered. However, I repeated running the problem for more than several days. I never hit the situation that the assertion (assert(z.load()!=0);) fires. I just use the default optimization and compile the code using g++ -std=c++11 -lpthread dataRaceAtomic.cpp Does anyone actually try it and hit the assertion? Could anyone give me an explanation about my test results? BTW, I also tried the version without using the atomic type, I got the same result. Currently, both programs are running healthily. Thanks.

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  • How to cast C struct just another struct type if their memory size are equal?

    - by Eonil
    I have 2 matrix structs means equal data but have different form like these: // Matrix type 1. typedef float Scalar; typedef struct { Scalar e[4]; } Vector; typedef struct { Vector e[4]; } Matrix; // Matrix type 2 (you may know this if you're iPhone developer) struct CATransform3D { CGFloat m11, m12, m13, m14; CGFloat m21, m22, m23, m24; CGFloat m31, m32, m33, m34; CGFloat m41, m42, m43, m44; }; typedef struct CATransform3D CATransform3D; Their memory size are equal. So I believe there is a way to convert these types without any pointer operations or copy like this: // Implemented from external lib. CATransform3D CATransform3DMakeScale (CGFloat sx, CGFloat sy, CGFloat sz); Matrix m = (Matrix)CATransform3DMakeScale ( 1, 2, 3 ); Is this possible? Currently compiler prints an "error: conversion to non-scalar type requested" message.

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  • Android - save/restore state of custom class

    - by user1209216
    I have some class for ssh support - it uses jsch internally. I use this class on main activity, this way: public class MainActivity extends Activity { SshSupport ssh = new SshSupport(); ..... @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); //Handle events for ssh ssh.eventHandler = new ISshEvents() { @Override public void SshCommandExecuted(SshCommandsEnum commandType, String result) { } //other overrides here } //Ssh operations on gui item click @Override public void onItemClick(AdapterView<?> arg0, View v, int position, long arg3) { if (ssh.IsConnected() == false) { try { ssh.ConnectAsync(/*parameters*/); } catch (Exception e) { e.printStackTrace(); } } try { ssh.ExecuteCommandAsync(SshCommandsEnum.values()[position]); } catch (Exception e) { e.printStackTrace(); } } }); } It works very well. My application connects to ssh, performs all needed operation in background thread and results are reported to gui, via events as shown above. But nothing works after user change device orientation. It's clear for me - activity is re-created and all state is lost. Unfortunately, my SshSupport class object is lost as well. It's pretty easy to store gui state for dynamically changed/added objects (using put/get serializable etc methods). But I have no idea how to prevent my ssh object, ssh connected session being lost. Since my class is not serializable, I can't save it to bundle. Also, even if I make my SshSupport class serializable, jsch objects it uses still are not serializable. So what is the best way to solve this?

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  • Getting problem in threading in JAVA

    - by chetans
    In this program i want to stop GenerateImage & MovingImage Thread both... And i want to start those threads from begining. Can u send me the solution? Here is the code........ package Game; import java.applet.Applet; import java.awt.Color; import java.awt.Dimension; import java.awt.Graphics; import java.awt.Image; import java.awt.MediaTracker; import java.awt.event.KeyEvent; import java.awt.event.KeyListener; import java.net.MalformedURLException; import java.net.URL; public class ThreadInApplet extends Applet implements KeyListener { private static final long serialVersionUID = 1L; Image[] asteroidImage; Image spaceshipImage; String levelstr="Easy Level"; int[] XPos,YPos; int number=0,XPosOfSpaceship,YPosOfSpaceship,NoOfObstacles=5,speed=1,level=1,spaceBtnPressdCntr=0; boolean gameStart=false,pauseGame=false,collideUp=false,collideDown=false,collideLeft=false,collideRight=false; private Image offScreenImage; private Dimension offScreenSize; private Graphics offScreenGraphics; Thread GenerateImages,MoveImages; public void init() { try { GenerateImages=new Thread () //thread to create obstacles { synchronized public void run () { for(int g=0;g<NoOfObstacles;g++) { try { sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } number++; // Temporary counter to count the no of obstacles created } } } ; MoveImages=new Thread () //thread to move obstacles { @SuppressWarnings("deprecation") synchronized public void run () { while(YPos[NoOfObstacles-1]!=600) { pauseGame=false; if(collide()==true) { GenerateImages.suspend(); repaint(); } else GenerateImages.resume(); for(int l=0;l<number;l++) { if(collide()==false) YPos[l]++; else GenerateImages.suspend(); } repaint(); try { sleep(speed); } catch (InterruptedException e) { e.printStackTrace(); } } if(YPos[NoOfObstacles-1]>=600) //level complete state { level++; try { levelUpdation(level); System.out.println("aahe"); } catch (MalformedURLException e) { e.printStackTrace(); } repaint(); } } }; initialPos(); spaceshipImage=getImage(new URL(getCodeBase(),"images/space.png")); for(int i=0;i<NoOfObstacles;i++) { asteroidImage[i]=getImage(new URL(getCodeBase(),"images/asteroid.png")); XPos[i]=(int) (Math.random()*700); YPos[i]=0; } MediaTracker tracker = new MediaTracker (this); for(int i=0;i<NoOfObstacles;i++) { tracker.addImage (asteroidImage[i], 0); } } catch (MalformedURLException e) { e.printStackTrace(); } setBackground(Color.black); addKeyListener(this); } //Sets initial positions of spaceship & obstacle images------------------------------------------------------ public void initialPos() throws MalformedURLException { asteroidImage=new Image[NoOfObstacles]; XPos=new int[NoOfObstacles]; YPos=new int[NoOfObstacles]; XPosOfSpaceship=getWidth()/2-35; YPosOfSpaceship=getHeight()-100; collideUp = false; collideDown=false; collideLeft=false; collideRight=false; } //level finished updations------------------------------------------------------------------------------ @SuppressWarnings("deprecation") public void levelUpdation(int level) throws MalformedURLException { NoOfObstacles=NoOfObstacles+20; speed=speed-3; System.out.println(NoOfObstacles+" "+speed); pauseGame=true; initialPos(); repaint(); } //paint method of graphics to print the messages--------------------------------------------------------- public void paint(Graphics g) { g.setColor(Color.white); if(gameStart==false) { g.drawString("SPACE to start", (getWidth()/2)-15, getHeight()/2); g.drawString(levelstr, (getWidth()/2), getHeight()/2+20); } if(level>1) { if(level==2) levelstr="Medium Level"; else levelstr="High Level"; g.drawString("Level Complete ", (getWidth()/2)-15, getHeight()/2); g.drawString(levelstr, (getWidth()/2), getHeight()/2+20); //g.drawString("SPACE to start", (getWidth()/2)-15, getHeight()/2+40); } for(int n=0;n<number;n++) { if(n>0) g.drawImage(asteroidImage[n],XPos[n],YPos[n],this); } g.drawImage(spaceshipImage,XPosOfSpaceship,YPosOfSpaceship,this); } //update method of graphics to print the messages--------------------------------------------------------- @SuppressWarnings("deprecation") public void update(Graphics g) { Dimension d = size(); if((offScreenImage == null) || (d.width != offScreenSize.width) || (d.height != offScreenSize.height)) { offScreenImage = createImage(d.width, d.height); offScreenSize = d; offScreenGraphics = offScreenImage.getGraphics(); } offScreenGraphics.clearRect(0, 0, d.width, d.height); paint(offScreenGraphics); g.drawImage(offScreenImage, 0, 0, null); } public void keyReleased(KeyEvent arg0){} public void keyTyped(KeyEvent arg0) {} //---------------------Key pressed event to start game & to move the spaceship-------------------------------------- public void keyPressed(KeyEvent e) { if(e.getKeyCode()==32) { spaceBtnPressdCntr++; if(spaceBtnPressdCntr==1) { gameStart=true; GenerateImages.start(); MoveImages.start(); } } if(gameStart==true) { if(e.getKeyCode()==37) { new Thread () { @SuppressWarnings("deprecation") synchronized public void run () { for(int cnt1=1;cnt1<=10;cnt1++) { if(collide()==true && collideLeft == true) { GenerateImages.suspend(); } else { if(XPosOfSpaceship>0) XPosOfSpaceship--; } } repaint(); } }.start(); } if(e.getKeyCode()==38) { new Thread () { @SuppressWarnings("deprecation") synchronized public void run () { for(int cnt1=1;cnt1<=10;cnt1++) { if(collide()==true && collideUp == true) { GenerateImages.suspend(); } else { if(YPosOfSpaceship>10) YPosOfSpaceship--; } } repaint(); } }.start(); } if(e.getKeyCode()==39) { new Thread () { @SuppressWarnings("deprecation") synchronized public void run () { for(int cnt1=1;cnt1<=10;cnt1++) { if(collide()==true && collideRight == true) { GenerateImages.suspend(); } else { if(XPosOfSpaceship<750) XPosOfSpaceship++; } } repaint(); } }.start(); } if(e.getKeyCode()==40) { new Thread () { @SuppressWarnings("deprecation") synchronized public void run () { for(int cnt1=1;cnt1<=10;cnt1++) { if(collide()==true && collideDown == true) { GenerateImages.suspend(); } else { if(YPosOfSpaceship<550) YPosOfSpaceship++; } } repaint(); } }.start(); } } } //------------------------------Collision checking between Spaceship & obstacles------------------------------ public boolean collide() { int x1,y1,x2,y2,x3,y3,x4,y4; //coordinates of obstacles int a1,b1,a2,b2,a3,b3,a4,b4; //coordinates of spaceship a1 =XPosOfSpaceship; b1=YPosOfSpaceship; a2=a1+spaceshipImage.getWidth(this); b2=b1; a3=a1; b3=b1+spaceshipImage.getHeight(this); a4=a2; b4=b3; for(int a=0;a<number;a++) { x1 =XPos[a]; y1=YPos[a]; x2=x1+asteroidImage[a].getWidth(this); y2=y1; x3=x1; y3=y1+asteroidImage[a].getHeight(this); x4=x2; y4=y3; /********checking asteroid touch spaceship from up direction********/ if(y3==b1 && x4>=a1 && x4<=a2) { collideUp = true; collideDown=false; collideLeft=false; collideRight=false; return(true); } if(y3==b1 && x3>=a1 && x3<=a2) { collideUp = true; collideDown=false; collideLeft=false; collideRight=false; return(true); } /********checking asteroid touch spaceship from left direction******/ if(x2==a1 && y4>=b1 && y4<=b3) { collideLeft=true; collideUp = false; collideDown=false; collideRight=false; return(true); } if(x2==a1 && y2>=b1 && y2<=b3) { collideLeft=true; collideUp = false; collideDown=false; collideRight=false; return(true); } /********checking asteroid touch spaceship from right direction*****/ if(x1==a2 && y3>=b2 && y3<=b4) { collideRight=true; collideLeft=false; collideUp = false; collideDown=false; return(true); } if(x1==a2 && y1>=b2 && y1<=b4) { collideRight=true; collideLeft=false; collideUp = false; collideDown=false; return(true); } /********checking asteroid touch spaceship from down direction*****/ if(y1==b3 && x2>=a3 && x2<=a4) { collideDown=true; collideRight=false; collideLeft=false; collideUp = false; return(true); } if(y1==b3 && x1>=a3 && x1<=a4) { collideDown=true; collideRight=false; collideLeft=false; collideUp = false; return(true); } } return(false); } }

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  • In ActionScript, is there a way to test for existence of variable with datatype "Function"

    - by Robusto
    So I have a class where I instantiate a variable callback like so: public var callback:Function; So far so good. Now, I want to add an event listener to this class and test for existence of the callback. I'm doing like so: this.addEventListener(MouseEvent.MOUSE_OVER, function(event:MouseEvent) : void { if (callback) { // do some things } }); This works great, doesn't throw any errors, but everywhere I test for callback I get the following warning: 3553: Function value used where type Boolean was expected. Possibly the parentheses () are missing after this function reference. That bugged me, so I tried to get rid of the warning by testing for null and undefined. Those caused errors. I can't instantiate a Function as null, either. I know, I know, real programmers only care about errors, not warnings. I will survive if this situation is not resolved. But it bothers me! :) Am I just being neurotic, or is there actually some way to test whether a real Function has been created without the IDE bitching about it?

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  • Immutability and shared references - how to reconcile?

    - by davetron5000
    Consider this simplified application domain: Criminal Investigative database Person is anyone involved in an investigation Report is a bit of info that is part of an investigation A Report references a primary Person (the subject of an investigation) A Report has accomplices who are secondarily related (and could certainly be primary in other investigations or reports These classes have ids that are used to store them in a database, since their info can change over time (e.g. we might find new aliases for a person, or add persons of interest to a report) If these are stored in some sort of database and I wish to use immutable objects, there seems to be an issue regarding state and referencing. Supposing that I change some meta-data about a Person. Since my Person objects immutable, I might have some code like: class Person( val id:UUID, val aliases:List[String], val reports:List[Report]) { def addAlias(name:String) = new Person(id,name :: aliases,reports) } So that my Person with a new alias becomes a new object, also immutable. If a Report refers to that person, but the alias was changed elsewhere in the system, my Report now refers to the "old" person, i.e. the person without the new alias. Similarly, I might have: class Report(val id:UUID, val content:String) { /** Adding more info to our report */ def updateContent(newContent:String) = new Report(id,newContent) } Since these objects don't know who refers to them, it's not clear to me how to let all the "referrers" know that there is a new object available representing the most recent state. This could be done by having all objects "refresh" from a central data store and all operations that create new, updated, objects store to the central data store, but this feels like a cheesy reimplementation of the underlying language's referencing. i.e. it would be more clear to just make these "secondary storable objects" mutable. So, if I add an alias to a Person, all referrers see the new value without doing anything. How is this dealt with when we want to avoid mutability, or is this a case where immutability is not helpful?

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  • Can Haskell's monads be thought of as using and returning a hidden state parameter?

    - by AJM
    I don't understand the exact algebra and theory behind Haskell's monads. However, when I think about functional programming in general I get the impression that state would be modelled by taking an initial state and generating a copy of it to represent the next state. This is like when one list is appended to another; neither list gets modified, but a third list is created and returned. Is it therefore valid to think of monadic operations as implicitly taking an initial state object as a parameter and implicitly returning a final state object? These state objects would be hidden so that the programmer doesn't have to worry about them and to control how they gets accessed. So, the programmer would not try to copy the object representing the IO stream as it was ten minutes ago. In other words, if we have this code: main = do putStrLn "Enter your name:" name <- getLine putStrLn ( "Hello " ++ name ) ...is it OK to think of the IO monad and the "do" syntax as representing this style of code? putStrLn :: IOState -> String -> IOState getLine :: IOState -> (IOState, String) main :: IOState -> IOState -- main returns an IOState we can call "state3" main state0 = putStrLn state2 ("Hello " ++ name) where (state2, name) = getLine state1 state1 = putStrLn state0 "Enter your name:"

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  • recvfrom returns invalid argument when *from* is passed

    - by Aditya Sehgal
    I am currently writing a small UDP server program in linux. The UDP server will receive packets from two different peers and will perform different operations based on from which peer it received the packet. I am trying to determine the source from where I receive the packet. However, when select returns and recvfrom is called, it returns with an error of Invalid Argument. If I pass NULL as the second last arguments, recvfrom succeeds. I have tried declaring fromAddr as struct sockaddr_storage, struct sockaddr_in, struct sockaddr without any success. Is their something wrong with this code? Is this the correct way to determine the source of the packet? The code snippet follows. ` /*TODO : update for TCP. use recv */ if((pkInfo->rcvLen=recvfrom(psInfo->sockFd, pkInfo->buffer, MAX_PKTSZ, 0, /* (struct sockaddr*)&fromAddr,*/ NULL, &(addrLen) )) < 0) { perror("RecvFrom failed\n"); } else { /*Apply Filter */ #if 0 struct sockaddr_in* tmpAddr; tmpAddr = (struct sockaddr_in* )&fromAddr; printf("Received Msg From %s\n",inet_ntoa(tmpAddr->sin_addr)); #endif printf("Packet Received of len = %d\n",pkInfo->rcvLen); } `

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  • How to Prevent PostBack Event Handler from Firing

    - by user331744
    I have a custom class (ServerSideValidator.vb) that validates user input on server side (it doesn't use any of the .NET built in validators, therefore Page.Validate() is not an option for me). I am calling the Validate() method on page.IsPostback event and the class performs without any problem My issue is, when validation fails (returns false), I want to stop the postback event handler from firing, but load the page along with all the controls and user-input values in them. If I do, Response.End(), the page comes up blank. I can programmatically instruct the page to go to the previous page (original form before postback), but it loses all user-inputs. I thought of creating a global boolean variable in the page code behind file and check the value before performing any postback method, but this approach takes away from my plan to provide all functionalities inside the class itself. The page object is being referenced to ServerSideValidator. Seems like all the postback related properties/variables I come across inside Page class are 'Readonly' and I can't assign value(s) to control/prevent postback event from firing. Any idiea on how I can accomplish this? Please let me know if you need further details

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  • Creating multiple instances of a generic database

    - by sagekilla
    Hi all, currently I'm trying to have a setup where a generic database is distributed to students. They would develop an application using this database (Say a shopping cart application), submit their project onto our server, and then it would be graded automatically. These databases are being run in Microsoft SQL Server 2005. We're using user instances to instantiate each database, and multiple requests could be serviced at once. But, the problem is when more than one student submitted a project to be graded, the first database to be instantiated would be the only one and would overwrite all other copies that were currently open. So if stu1 modified his database and stu2 and stu3 had their projects being graded concurrently, at the end of the grading stu1, stu2, and stu3 would have identical DB's at the end. Is there any way I can have multiple independent copies of a generic database, each of which I can load concurrently and modify without having any changes made to any one affecting the others? I did a little reading, and thought it might be possible to do something along the lines of: Student submits project Attach the database with unique db name (specified by student) Do all necessary operations Detach the database I'm unsure if this would fix our problem or be possible, so any help would be much appreciated!

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  • highlight listview items android

    - by user1752939
    I have listview with custom base adapter. When I populate the list I have to check a boolean in the object I'm populating the listview and if it is true to change the background color of that row. public View getView(int position, View convertView, ViewGroup parent) { LoginsList entry = listOfLoginsLists.get(position); if (convertView == null) { LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE); convertView = inflater.inflate(R.layout.lists_row, null); } TextView ListName = (TextView) convertView.findViewById(R.id.tvListName); ListName.setText(entry.getListName()); TextView ListDescription = (TextView) convertView.findViewById(R.id.tvListDescription); ListDescription.setText(entry.getListDescription()); Button Send = (Button) convertView.findViewById(R.id.bSend); Send.setOnClickListener(this); Send.setTag(entry); RelativeLayout RelLayout = (RelativeLayout) convertView.findViewById(R.id.layoutListsRow); RelLayout.setFocusableInTouchMode(false); RelLayout.setFocusable(false); RelLayout.setOnClickListener(this); RelLayout.setTag(entry); if (entry.isSent()) { RelLayout.setBackgroundColor(Color.parseColor("#4400FF00")); } return convertView; } But this code doesn't work right. When I scroll the list view the rows colors get messed up.

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  • Symfony 2 - Updating a table based on newly inserted record in another table

    - by W00d5t0ck
    I'm trying to create a small forum application using Symfony 2 and Doctrine 2. My ForumTopic entity has a last_post field (oneToOne mapping). Now when I persist my new post with $em->persist($post); I want to update my ForumTopic entity so its last_post field would reference this new post. I have just realised that it cannot be done with a Doctrine postPersist Listener, so I decided to use a small hack, and tried: $em->persist($post); $em->flush(); $topic->setLastPost($post); $em->persist($post); $em->flush(); but it doesn't seem to update my topics table. I also took a look at http://docs.doctrine-project.org/projects/doctrine-orm/en/2.1/reference/working-with-associations.html#transitive-persistence-cascade-operations hoping it will solve the problem by adding cascade: [ 'persist' ] to my Topic.orm.yml file, but it didn't help, either. Could anyone point me to a solution or an example class? My ForumTopic is: FrontBundle\Entity\ForumTopic: type: entity table: forum_topics id: id: type: integer generator: strategy: AUTO fields: title: type: string(100) nullable: false slug: type: string(100) nullable: false created_at: type: datetime nullable: false updated_at: type: datetime nullable: true update_reason: type: text nullable: true oneToMany: posts: targetEntity: ForumPost mappedBy: topic manyToOne: created_by: targetEntity: User inversedBy: articles nullable: false updated_by: targetEntity: User nullable: true default: null topic_group: targetEntity: ForumTopicGroup inversedBy: topics nullable: false oneToOne: last_post: targetEntity: ForumPost nullable: true default: null cascade: [ persist ] uniqueConstraint: uniqueSlugByGroup: columns: [ topic_group, slug ] And my ForumPost is: FrontBundle\Entity\ForumPost: type: entity table: forum_posts id: id: type: integer generator: strategy: AUTO fields: created_at: type: datetime nullable: false updated_at: type: datetime nullable: true update_reason: type: string nullable: true text: type: text nullable: false manyToOne: created_by: targetEntity: User inversedBy: forum_posts nullable: false updated_by: targetEntity: User nullable: true default: null topic: targetEntity: ForumTopic inversedBy: posts

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  • Java Days & Bookings

    - by sys_debug
    Ok this is an extension of a question I asked about earlier yet this is the next step that is unclear to me. Everything else will be ready and this part is driving me mad! some members provided great help and I already made progress with that info, but this is just another obstacle. I am creating a booking object (as was suggested) that will have a start date and end date. each booking will also have a number of seats associated with it (that I require to reserve). The total available number of seats any given day 46 (as the total capacity of the hall is 46 seats). so in assumption that I have a booking to be made in the system, and start date is 1st jan and end date is 10th jan. The question is how can I check the remaining seats in all those days between the range to see if requested number could be hosted or not? and then when the second booking is made, it will have to see that the days in this range already have less than 46 and decrement further if possible to host the reservation. one of the members, and I appreciate his effort, gladly contributed a method to compare if this booking is after or before the existing bookings. The code provided is here: public boolean overlapsWithExisting(Booking booking) { final Date early = booking.getStart(); final Date late = booking.getEnd(); for(Booking existing : existingBookings) { if(!(early.isAfter(existing.getEnd() || late.isBefore(existing.getStart())) return true; } return false; } I just want to know how to associate 46 with each day and keep record of days that are decremented by bookings. Thanks and reallllllly appreciated :D

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  • Is locking on the requested object a bad idea?

    - by Quick Joe Smith
    Most advice on thread safety involves some variation of the following pattern: public class Thing { private static readonly object padlock = new object(); private string stuff, andNonsense; public string Stuff { get { lock (Thing.padlock) { if (this.stuff == null) this.stuff = "Threadsafe!"; } return this.stuff; } } public string AndNonsense { get { lock (Thing.padlock) { if (this.andNonsense == null) this.andNonsense = "Also threadsafe!"; } return this.andNonsense; } } // Rest of class... } In cases where the get operations are expensive and unrelated, a single locking object is unsuitable because a call to Stuff would block all calls to AndNonsense, degrading performance. And rather than create a lock object for each call, wouldn't it be better to acquire the lock on the member itself (assuming it is not something that implements SyncRoot or somesuch for that purpose? For example: public string Stuff { get { lock (this.stuff) { // Pretend that this is a very expensive operation. if (this.stuff == null) this.stuff = "Still threadsafe and good?"; } return this.stuff; } } Strangely, I have never seen this approach recommended or warned against. Am I missing something obvious?

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  • CAML query returns wrong results?

    - by Abe Miessler
    I have the following code: SPQuery oQuery = new SPQuery(); oQuery.Query = @"<Query> <Where> <And> <Eq> <FieldRef Name='PublishToSM' /> <Value Type='Boolean'>1</Value> </Eq> <IsNull> <FieldRef Name='SMUpdateDate' /> </IsNull> </And> </Where> </Query>"; SPListItemCollection collListItems = list.GetItems(oQuery); NevCoSocialMedia.NevCoFacebook fb = new NevCoSocialMedia.NevCoFacebook(); foreach (SPListItem oListItem in collListItems) { if (oListItem.Fields.ContainsField("PublishToSM") && Convert.ToBoolean(oListItem["PublishToSM"]) == true) { . . . My question is why do I need to have the last if statement? If I don't have this it will throw an error saying that the identifier does not exist when it tries to do oListItem["PublishToSM"]. This seems impossible since my CAML query is checking that that has an appropriate value...

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  • Efficient database access when dealing with multiple abstracted repositories

    - by Nathan Ridley
    I want to know how most people are dealing with the repository pattern when it involves hitting the same database multiple times (sometimes transactionally) and trying to do so efficiently while maintaining database agnosticism and using multiple repositories together. Let's say we have repositories for three different entities; Widget, Thing and Whatsit. Each repository is abstracted via a base interface as per normal decoupling design processes. The base interfaces would then be IWidgetRepository, IThingRepository and IWhatsitRepository. Now we have our business layer or equivalent (whatever you want to call it). In this layer we have classes that access the various repositories. Often the methods in these classes need to do batch/combined operations where multiple repositories are involved. Sometimes one method may make use of another method internally, while that method can still be called independently. What about, in this scenario, when the operation needs to be transactional? Example: class Bob { private IWidgetRepository _widgetRepo; private IThingRepository _thingRepo; private IWhatsitRepository _whatsitRepo; public Bob(IWidgetRepository widgetRepo, IThingRepository thingRepo, IWhatsitRepository whatsitRepo) { _widgetRepo = widgetRepo; _thingRepo= thingRepo; _whatsitRepo= whatsitRepo; } public void DoStuff() { _widgetRepo.StoreSomeStuff(); _thingRepo.ReadSomeStuff(); _whatsitRepo.SaveSomething(); } public void DoOtherThing() { _widgetRepo.UpdateSomething(); DoStuff(); } } How do I keep my access to that database efficient and not have a constant stream of open-close-open-close on connections and inadvertent invocation of MSDTS and whatnot? If my database is something like SQLite, standard mechanisms like creating nested transactions are going to inherently fail, yet the business layer should not have to be concerning itself with such things. How do you handle such issues? Does ADO.Net provide simple mechanisms to handle this or do most people end up wrapping their own custom bits of code around ADO.Net to solve these types of problems?

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  • Any Alternate way for writing to a file other than ofstream

    - by Aditya
    Hi All, I am performing file operations (writeToFile) which fetches the data from a xml and writes into a output file(a1.txt). I am using MS Visual C++ 2008 and in windows XP. currently i am using this method of writing to output file.. 01.ofstreamhdr OutputFile; 02./* few other stmts / 03.hdrOutputFile.open(fileName, std::ios::out); 04. 05.hdrOutputFile << "#include \"commondata.h\""<< endl ; 06.hdrOutputFile << "#include \"Commonconfig.h\"" << endl ; 07.hdrOutputFile << "#include \"commontable.h\"" << endl << endl ; 08. hdrOutputFile << "#pragma pack(push,1)" << endl ; 09.hdrOutputFile << "typedef struct \n {" << endl ; 10./ simliar hdrOutputFiles statements... */.. I have around 250 lines to write.. Is any better way to perform this task. I want to reduce this hdrOutputFile and use a buffer to do this. Please guide me how to do that action. I mean, buff = "#include \"commontable.h\"" + "typedef struct \n {" + ....... hdrOutputFile << buff. is this way possible? Thanks Ramm

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  • How string accepting interface should look like?

    - by ybungalobill
    Hello, This is a follow up of this question. Suppose I write a C++ interface that accepts or returns a const string. I can use a const char* zero-terminated string: void f(const char* str); // (1) The other way would be to use an std::string: void f(const string& str); // (2) It's also possible to write an overload and accept both: void f(const char* str); // (3) void f(const string& str); Or even a template in conjunction with boost string algorithms: template<class Range> void f(const Range& str); // (4) My thoughts are: (1) is not C++ish and may be less efficient when subsequent operations may need to know the string length. (2) is bad because now f("long very long C string"); invokes a construction of std::string which involves a heap allocation. If f uses that string just to pass it to some low-level interface that expects a C-string (like fopen) then it is just a waste of resources. (3) causes code duplication. Although one f can call the other depending on what is the most efficient implementation. However we can't overload based on return type, like in case of std::exception::what() that returns a const char*. (4) doesn't work with separate compilation and may cause even larger code bloat. Choosing between (1) and (2) based on what's needed by the implementation is, well, leaking an implementation detail to the interface. The question is: what is the preffered way? Is there any single guideline I can follow? What's your experience?

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  • Adding a Way To preserve A Comma In A CSV To DataTable Function

    - by Nick LaMarca
    I have a function that converts a .csv file to a datatable. One of the columns I am converting is is a field of names that have a comma in them i.e. "Doe, John" when converting the function treats this as 2 seperate fields because of the comma. I need the datatable to hold this as one field Doe, John in the datatable. Function CSV2DataTable(ByVal filename As String, ByVal sepChar As String) As DataTable Dim reader As System.IO.StreamReader Dim table As New DataTable Dim colAdded As Boolean = False Try ''# open a reader for the input file, and read line by line reader = New System.IO.StreamReader(filename) Do While reader.Peek() >= 0 ''# read a line and split it into tokens, divided by the specified ''# separators Dim tokens As String() = System.Text.RegularExpressions.Regex.Split _ (reader.ReadLine(), sepChar) ''# add the columns if this is the first line If Not colAdded Then For Each token As String In tokens table.Columns.Add(token) Next colAdded = True Else ''# create a new empty row Dim row As DataRow = table.NewRow() ''# fill the new row with the token extracted from the current ''# line For i As Integer = 0 To table.Columns.Count - 1 row(i) = tokens(i) Next ''# add the row to the DataTable table.Rows.Add(row) End If Loop Return table Finally If Not reader Is Nothing Then reader.Close() End Try End Function

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  • How to convert a rectangle to TRBL CSS rect value?

    - by VLostBoy
    I'm not quite sure how to put this, but here goes... The css clip attribute is defined like so: rect(top, right, bottom, left). However, I'm exploring the use of a custom Rectangle 'class' to encapsulate some operations. The rectangle class has the attributes height, width and x, y. The x and y values are encapsulated in a Point object, and the height and width are encapsulated in a Dimension object, the rectangle being a composite of a point (its top-left location) and a dimension (width and height). So far so good. I though it would be pretty simple on the basis of having the rectangles x, y, width and height values to define the css rect attribute in terms of top, right, bottom, left, but I've become hopelessly confused- I've been googling for a while, and I can't seem to find any documentation as to what the TRBL values actually are or what they represent. For example, should I be thinking in terms of co-ordinates, in which case, surely I can describe the rectangle as a css rect using the rectangles x position for Top, x position + width for Right, the rectangles height + y for Bottom and its y position for Left... but thats a load of BS, surely? Also, surely rect is actually an inset, or have I just inverted my understanding of clip? I'd appreciate some advice. What I want to be able to do is (i) Define a rectangle using x, y, width and height (ii)Express the rectangle in TRBL form so that I can manipulate a divs clipping behaviour (iii)Change x, y, width or height and recalculate in terms of TRBL and goto (ii) I appreciate there are some other factors here, and some intermediary transforms to be done, but I've confused myself pretty badly- Can anyone give me some pointers?

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  • Deterministic floating point and .NET

    - by code2code
    How can I guarantee that floating point calculations in a .NET application (say in C#) always produce the same bit-exact result? Especially when using different versions of .NET and running on different platforms (x86 vs x86_64). Inaccuracies of floating point operations do not matter. In Java I'd use strictfp. In C/C++ and other low level languages this problem is essentially solved by accessing the FPU / SSE control registers but that's probably not possible in .NET. Even with control of the FPU control register the JIT of .NET will generate different code on different platforms. Something like HotSpot would be even worse in this case... Why do I need it? I'm thinking about writing a real-time strategy (RTS) game which heavily depends on fast floating point math together with a lock stepped simulation. Essentially I will only transmit user input across the network. This also applies to other games which implement replays by storing the user input. Not an option are: decimals (too slow) fixed point values (too slow and cumbersome when using sqrt, sin, cos, tan, atan...) update state across the network like an FPS: Sending position information for hundreds or a few thousand units is not an option Any ideas?

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  • How to write a "thread safe" function in C ?

    - by Andrei Ciobanu
    Hello I am writing some data structures in C, and I've realized that their associated functions aren't thread safe. The i am writing code uses only standard C, and I want to achieve some sort of 'synchronization'. I was thinking to do something like this: enum sync_e { TRUE, FALSE }; typedef enum sync_e sync; struct list_s { //Other stuff struct list_node_s *head; struct list_node_s *tail; enum sync_e locked; }; typedef struct list_s list; , to include a "boolean" field in the list structure that indicates the structures state: locked, unlocked. For example an insertion function will be rewritten this way: int list_insert_next(list* l, list_node *e, int x){ while(l->locked == TRUE){ /* Wait */ } l->locked = TRUE; /* Insert element */ /* -------------- */ l->locked = FALSE; return (0); } While operating on the list the 'locked' field will be set to TRUE, not allowing any other alterations. After operation completes the 'locked' field will be again set to 'TRUE'. Is this approach good ? Do you know other approaches (using only standard C).

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  • Why is textbox.focus throwing the lostfocus event?

    - by cost
    I've seen a few similar questions on SO but nothing that seems to actually address the issue. Here's a simplified version of the function. Private Sub Check_Quantity(sender As System.Object, e As System.Windows.RoutedEventArgs) _ Handles textbox_quantity.LostFocus Dim worked As Boolean = Integer.TryParse(textbox_quantity.Text, quantity) If Not worked Then MsgBox("Enter a valid number for the quantity") textbox_quantity.Focus() textbox_quantity.SelectAll() quantity = 0 End If End Sub It's important to note that this is WPF. What I want to do is very simple. When someone finishes with the textbox the program checks that what they entered is a number. If it does it sticks this in an integer. If not, it tells them to fix it and keeps the focus on the textbox. The issue is a few things, but what it comes down to is this function runs in an infinite loop. This same function works fine in WinForms, but not in WPF. On some other questions people have said that the messagebox appearing causes focus to be lost, but in testing this isn't true. It still loops regardless of if the messagebox is called or not. The problem is the call to textbox_quantity.Focus(). Without that it works fine. Regardless of whether it's there or not though, focus is not set to the textbox, though textbox_quantity.Focus() still returns a value of true. Any thought of what's going on and maybe how I could fix it?

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