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  • asking the container to notify your application whenever a session is about to timeout in Java

    - by user136101
    Which method(s) can be used to ask the container to notify your application whenever a session is about to timeout?(choose all that apply) A. HttpSessionListener.sessionDestroyed -- correct B. HttpSessionBindingListener.valueBound C. HttpSessionBindingListener.valueUnbound -- correct this is kind of round-about but if you have an attribute class this is a way to be informed of a timeout D. HttpSessionBindingEvent.sessionDestroyed -- no such method E. HttpSessionAttributeListener.attributeRemoved -- removing an attribute isn’t tightly associated with a session timeout F. HttpSessionActivationListener.sessionWillPassivate -- session passivation is different than timeout I agree with option A. 1) But C is doubtful How can value unbound be tightly coupled with session timeout.It is just the callback method when an attribute gets removed. 2) and if C is correct, E should also be correct. HttpSessionAttributeListener is just a class that wants to know when any type of attribute has been added, removed, or replaced in a session. It is implemented by any class. HttpSessionBindingListener exists so that the attribute itself can find out when it has been added to or removed from a session and the attribute class must implement this interface to achieve it. Any ideas…

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  • Strange problem with simple multithreading program in Java

    - by Elizabeth
    Hello, I am just starting play with multithreading programming. I would like to my program show alternately character '-' and '+' but it doesn't. My task is to use synchronized keyword. As far I have: class FunnyStringGenerator{ private char c; public FunnyStringGenerator(){ c = '-'; } public synchronized char next(){ if(c == '-'){ c = '+'; } else{ c = '-'; } return c; } } class ThreadToGenerateStr implements Runnable{ FunnyStringGenerator gen; public ThreadToGenerateStr(FunnyStringGenerator fsg){ gen = fsg; } @Override public void run() { for(int i = 0; i < 10; i++){ System.out.print(gen.next()); } } } public class Main{ public static void main(String[] args) throws IOException { FunnyStringGenerator FSG = new FunnyStringGenerator(); ExecutorService exec = Executors.newCachedThreadPool(); for(int i = 0; i < 20; i++){ exec.execute(new ThreadToGenerateStr(FSG)); } } } EDIT: I also testing Thread.sleep in run method instead for loop.

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  • Accessing every child class of parent class in Java

    - by darkie15
    Hi All, I have to implement a logic whereby given a child class, I need to access its parent class and all other child class of that parent class, if any. I did not find any API in Java Reflection which allows us to access all child classes of a parent class. Is there any way to do it? Ex. class B extends class A class C extends class A Now using class B, I can find the superclass by calling getSuperClass(). But is there any way to find all the child classes once I have the parent class i.e. class B and class C?? Regards, darkie

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  • Socket programming question

    - by dfddf
    I am given the following declaration: char inbuff[500], *ptr; int n, bufferlen; Write a program segement to receive a message having 500 bits from the TCP socket sock and store this message in inbuff. My answer is: n = recv( sock, inbuff, strlen( inbuff ), 0 ); However, I am not sure why *ptr is given in the declaration. So, I would like ask, what is the purpose of the pointer in this question?? Or my program segement is wrong? Thank you for all of yours help first!

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  • Java - How to declare table[i][j] elements as instance variables?

    - by JDelage
    All, I am trying to code a Connect4 game. For this, I have created a P4Game class and a P4Board class which represents the i X j dimensions of the Connect4 board. In P4Game, I have the following: public class P4Game{ //INSTANCE VARIABLES private int nbLines; private int nbColumns; private P4Board [][] position; //CONSTRUCTOR public P4Game(int nbLines, int nbColumns){ this.nbColumns = nbColumns; this.nbLines = nbLines; P4Board [][] position = new P4Board [nbLines][nbColumns]; //Creates the table to receive the instances of the P4Board object.*/ for (int i=0; i<nbLines; i++){ for (int j=0; j<nbColumns; j++){ this.position[i][j] = new P4Board(i,j); //Meant to create each object at (line=i, column=j) } } } This causes a NullPointerException in the nested loops where I mention this.position[i][j]. I reference those objects in other methods of this class so I need them to be instance variables. I suppose the exception is due to the fact that I have not listed the table element position[i][j] as an instance variable at the beginning of the class. my question to people here is (1) is my assumption correct, and if so (2) what would be the syntax to declare instance variables of this form? Thank you all for your help with what I realize is a very basic question. Hopefully it will also benefit other newbies. Cheers, JDelage

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  • Where should I initialize variables for an OO Recursive Descent Parse Tree?

    - by Vasto
    I'd like to preface this by stating that this is for a class, so please don't solve this for me. One of my labs for my cse class is creating an interpreter for a BNF that was provided. I understand most of the concepts, but I'm trying to build up my tree and I'm unsure where to initialize values. I've tried in both the constructor, and in the methods but Eclipse's debugger still only shows the left branch, even though it runs through completely. Here is my main procedure so you can get an idea of how I'm calling the methods. public class Parser { public static void main(String[] args) throws IOException { FileTokenizer instance = FileTokenizer.Instance(); FileTokenizer.main(args); Prog prog = new Prog(); prog.ParseProg(); prog.PrintProg(); prog.ExecProg(); } Now here is My Prog class: public class Prog { private DeclSeq ds; private StmtSeq ss; Prog() { ds = new DeclSeq(); ss = new StmtSeq(); } public void ParseProg() { FileTokenizer instance = FileTokenizer.Instance(); instance.skipToken(); //Skips program (1) // ds = new DeclSeq(); ds.ParseDS(); instance.skipToken(); //Skips begin (2) // ss = new StmtSeq(); ss.ParseSS(); instance.skipToken(); } I've tried having Prog() { ds = null; ss = null; } public void ParseProg() { FileTokenizer instance = FileTokenizer.Instance(); instance.skipToken(); //Skips program (1) ds = new DeclSeq(); ds.ParseDS(); ... But it gave me the same error. I need the parse tree built up so I can do a pretty print and an execute command, but like I said, I only get the left branch. Any help would be appreciated. Explanations why are even more so appreciated. Thank you, Vasto

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  • How to access the relative directory of a ASP.NET website?

    - by Michael Schilling
    I need to access a folder that will contain various text files for my web site. I'm using Visual Web Developer 2010 Express. I made a web site using visual basic. Here is the failing code: Dim fileName As String fileName = CurDir.ToString + fileName.Text + ".txt" FileOpen(1, fileName, OpenMode.Output) FileClose(1) CurDir.ToString is giving me strange directory path that isn't anywhere near where my website files are located. I need to be able to access the files in a folder inside of the WebSite1 folder without using C:\Users\..., but I'm at a loss on how to do that. Can anyone help me out?

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  • BFS algorithm problem

    - by Gorkamorka
    The problem is as follows: A wanderer begins on the grid coordinates (x,y) and wants to reach the coordinates (0,0). From every gridpoint, the wanderer can go 8 steps north OR 3 steps south OR 5 steps east OR 6 steps west (8N/3S/5E/6W). How can I find the shortest route from (X,Y) to (0,0) using breadth-first search? Clarifications: Unlimited grid Negative coordinates are allowed A queue (linked list or array) must be used No obstacles present

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  • Still failing a function, not sure why...ideas on test cases to run?

    - by igor
    I've been trying to get this Sudoku game working, and I am still failing some of the individual functions. All together the game works, but when I run it through an "autograder", some test cases fail.. Currently I am stuck on the following function, placeValue, failing. I do have the output that I get vs. what the correct one should be, but am confused..what is something going on? EDIT: I do not know what input/calls they make to the function. What happens is that "invalid row" is outputted after every placeValue call, and I can't trace why.. Here is the output (mine + correct one) if it's at all helpful: http://pastebin.com/Wd3P3nDA Here is placeValue, and following is getCoords that placeValue calls.. void placeValue(Square board[BOARD_SIZE][BOARD_SIZE]) { int x,y,value; if(getCoords(x,y)) { cin>>value; if(board[x][y].permanent) { cout<< endl << "That location cannot be changed"; } else if(!(value>=1 && value<=9)) { cout << "Invalid number"<< endl; clearInput(); } else if(validMove(board, x, y, value)) { board[x][y].number=value; } } } bool getCoords(int & x, int & y) { char row; y=0; cin>>row>>y; x = static_cast<int>(toupper(row)); if (isalpha(row) && (x >= 'A' && x <= 'I') && y >= 1 && y <= 9) { x = x - 'A'; // converts x from a letter to corresponding index in matrix y = y - 1; // converts y to corresponding index in matrix return (true); } else if (!(x >= 'A' && x <= 'I')) { cout<<"Invalid row"<<endl; clearInput(); return false; } else { cout<<"Invalid column"<<endl; clearInput(); return false; } }

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  • Passing an array of structs in C

    - by lelouch
    I'm having trouble passing an array of structs to a function in C. I've created the struct like this in main: int main() { struct Items { char code[10]; char description[30]; int stock; }; struct Items MyItems[10]; } I then access it like: MyItems[0].stock = 10; etc. I want to pass it to a function like so: ReadFile(MyItems); The function should read the array, and be able to edit it. Then I should be able to access the same array from other functions. I've tried heaps of declarations but none of them work. e.g. void ReadFile(struct Items[10]) I've had a look around for other questions, but the thing is they're all done different, with typedefs and asterisks. My teacher hasn't taught us pointers yet, so I'd like to do it with what I know. Any ideas? :S EDIT: Salvatore's answer is working after I fixed my prototype to: void ReadFile(struct Items[9]);

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  • Problem with sending out variable to serial port using api JAVA

    - by sjaakensjon
    We are developing a java program for school. But we are experiencing problems with sending out a variable created by 3 sliders. The idea is that we have 3 sliders. One slider for every color. Red green and blue. The variable has to have a value between 0 and 255. Everytime the value of the slider changes is has to send a variable for the channel, that value is 1, 2 ,3. And after that it has to send the value of the slider through the serial port. Could you please help us out by creating an example program? Below is our code so far. Thanks in advance. Sjaak package main; import javax.swing.*; import javax.swing.event.*; import java.awt.*; import app.Com; import app.Parameters; public class menu{ JSlider sliderblauw; JLabel hoeveelblauw; JLabel blauw; JLabel rood; JSlider sliderrood; JLabel hoeveelrood; JLabel groen; JLabel hoeveelgroen; JSlider slidergroen; public menu(){ Frame venster = new JFrame("Color control"); JPanel blauwinstel = new JPanel(); ((JFrame) venster).setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); venster.setSize(500, 500); venster.setVisible(true); sliderblauw = new JSlider(JSlider.VERTICAL, 0, 255, 0); sliderblauw.addChangeListener(new veranderingblauw()); hoeveelblauw = new JLabel ("0"); blauwinstel.add(sliderblauw); blauwinstel.add(hoeveelblauw); venster.add(blauwinstel, BorderLayout.WEST); sliderblauw.setMajorTickSpacing(10); sliderblauw.setPaintTicks(true); JPanel roodinstel = new JPanel(); sliderrood = new JSlider(JSlider.VERTICAL, 0, 255, 0); sliderrood.addChangeListener(new veranderingrood()); hoeveelrood = new JLabel ("0"); roodinstel.add(sliderrood); roodinstel.add(hoeveelrood); venster.add(roodinstel, BorderLayout.EAST); sliderrood.setMajorTickSpacing(10); sliderrood.setPaintTicks(true); JPanel groeninstel = new JPanel(); slidergroen = new JSlider(JSlider.VERTICAL, 0, 255, 0); slidergroen.addChangeListener(new veranderinggroen()); hoeveelgroen = new JLabel ("0"); groeninstel.add(slidergroen); groeninstel.add(hoeveelgroen); venster.add(groeninstel, BorderLayout.CENTER); slidergroen.setMajorTickSpacing(10); slidergroen.setPaintTicks(true); } public class veranderingblauw implements ChangeListener{ public void stateChanged(ChangeEvent ce){ int value = sliderblauw.getValue(); String waarde_blauw = Integer.toString(value); hoeveelblauw.setText(waarde_blauw); }} public class veranderingrood implements ChangeListener{ public void stateChanged(ChangeEvent ce){ int value = sliderrood.getValue(); String waarde_rood = Integer.toString(value); hoeveelrood.setText(waarde_rood); }} public class veranderinggroen implements ChangeListener{ public void stateChanged(ChangeEvent ce){ int value = slidergroen.getValue(); String waarde_groen = Integer.toString(value); hoeveelgroen.setText(waarde_groen); }} public static void main( String[] args) { new menu(); } }

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  • Unresolved external symbol error in c++

    - by Crystal
    I am trying to do a simple hw problem involving namespace, static data members and functions. I am getting an unresolved external symbol error Error 1 error LNK2001: unresolved external symbol "private: static double JWong::SavingsAccount::annualInterestRate" (?annualInterestRate@SavingsAccount@JWong@@0NA) SavingsAccount.obj SavingsAccount And I don't see why I am getting this error. Maybe I don't know something about static variables compared to regular data members that is causing this error. Here is my code: SavingsAccount.h file #ifndef JWONG_SAVINGSACCOUNT_H #define JWONG_SAVINGSACCOUNT_H namespace JWong { class SavingsAccount { public: // default constructor SavingsAccount(); // constructor SavingsAccount(double savingsBalance); double getSavingsBalance(); void setSavingsBalance(double savingsBalance); double calculateMonthlyInterest(); // static functions static void modifyInterestRate(double newInterestRate); static double getAnnualInterestRest(); private: double savingsBalance; // static members static double annualInterestRate; }; } #endif SavingsAccount.cpp file #include <iostream> #include "SavingsAccount.h" // default constructor, set savingsBalance to 0 JWong::SavingsAccount::SavingsAccount() : savingsBalance(0) {} // constructor JWong::SavingsAccount::SavingsAccount(double savingsBalance) : savingsBalance(savingsBalance) {} double JWong::SavingsAccount::getSavingsBalance() { return savingsBalance; } void JWong::SavingsAccount::setSavingsBalance(double savingsBalance) { this->savingsBalance = savingsBalance; } // returns monthly interest and sets savingsBalance to new amount double JWong::SavingsAccount::calculateMonthlyInterest() { double monthlyInterest = savingsBalance * SavingsAccount::annualInterestRate / 12; setSavingsBalance(savingsBalance + monthlyInterest); return monthlyInterest; } void JWong::SavingsAccount::modifyInterestRate(double newInterestRate) { SavingsAccount::annualInterestRate = newInterestRate; } double JWong::SavingsAccount::getAnnualInterestRest() { return SavingsAccount::annualInterestRate; }

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  • c program for this quesion

    - by sashi
    suppose that a disk drive has 5000 cylinders, numbered 0 to 4999. the drive is currently serving a request at cylinder 143 and the previous request was at cylinder 125. the ueue of pending requests in the given order is 86,1470,913,17774,948,1509,1022,1750,130. write a 'c' program for finding the total distance in cylinders that the disk arm moves to satisfy all the pending reuests from the current heads position, using SSTF scheduling algorith. seek time is the time for the disk arm to move the head to the cylider containing the desired sector. sstf algorithm selects the minimum seek time from the current head position.

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  • Finding an available network port on the machine

    - by Tomer Vromen
    I'm trying to implement a simple FTP server (a variation of the EFTP protocol) in linux. When a client connects and sends the PASV command, the server should respond with a port number, so the client can connect to that port to transmit the file. How can the server choose a port number? Do I need to iterate through all the ports from 1024 to 65535 until I find a port that the process can bind to? I know that calling bind() with 0 as the port automatically chooses the port to bind to, but then how can I know which port was chosen? Many thanks.

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  • Pointers to class fields

    - by newbie_cpp
    My task is as follows : Using pointers to class fields, create menu allowing selection of ice, that Person can buy in Ice shop. Buyer will be charged with waffel and ice costs. Selection of ice and charging buyers account must be shown in program. Here's my Person class : #include <iostream> using namespace std; class Iceshop { const double waffel_price = 1; public: } class Person { static int NUMBER; char* name; int age; const int number; double plus, minus; public: class Account { int number; double resources; public: Account(int number, double resources) : number(number), resources(resources) {} } Person(const char* n, int age) : name(strcpy(new char[strlen(n)+1],n)), number(++NUMBER), plus(0), minus(0), age(age) {} Person::~Person(){ cout << "Destroying resources" << endl; delete [] name; } friend void show(Person &p); int* take_age(){ return &age; } char* take_name(){ return name; } void init(char* n, int a) { name = n; age = a; } Person& remittance(double d) { plus += d; return *this; } Person& paycheck(double d) { minus += d; return *this; } Account* getAccount(); }; int Person:: Person::Account* Person::getAccount() { return new Account(number, plus - minus); } void Person::Account::remittance(double d){ resources = resources + d; } void Person::Account::paycheck(double d){ resources = resources - d; } void show(Person *p){ cout << "Name: " << p->take_name() << "," << "age: " << p->take_age() << endl; } int main(void) { Person *p = new Person; p->init("Mary", 25); show(p); p->remittance(100); system("PAUSE"); return 0; } How to start this task ? Where and in what form should I store menu options ?

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  • Help with method logic in Java, hw

    - by Crystal
    I have a Loan class that in its printPayment method, it prints the amortization table of a loan for a hw assignment. We are also to implement a print first payment method, and a print last payment method. Since my calculation is done in the printPayment method, I didn't know how I could get the value in the first or last iteration of the loop and print that amount out. One way I can think of is to write a new method that might return that value, but I wasn't sure if there was a better way. Here is my code: public abstract class Loan { public void setClient(Person client) { this.client = client; } public Person getClient() { return client; } public void setLoanId() { loanId = nextId; nextId++; } public int getLoanId() { return loanId; } public void setInterestRate(double interestRate) { this.interestRate = interestRate; } public double getInterestRate() { return interestRate; } public void setLoanLength(int loanLength) { this.loanLength = loanLength; } public int getLoanLength() { return loanLength; } public void setLoanAmount(double loanAmount) { this.loanAmount = loanAmount; } public double getLoanAmount() { return loanAmount; } public void printPayments() { double monthlyInterest; double monthlyPrincipalPaid; double newPrincipal; int paymentNumber = 1; double monthlyInterestRate = interestRate / 1200; double monthlyPayment = loanAmount * (monthlyInterestRate) / (1 - Math.pow((1 + monthlyInterestRate),( -1 * loanLength))); System.out.println("Payment Number | Interest | Principal | Loan Balance"); // amortization table while (loanAmount >= 0) { monthlyInterest = loanAmount * monthlyInterestRate; monthlyPrincipalPaid = monthlyPayment - monthlyInterest; newPrincipal = loanAmount - monthlyPrincipalPaid; loanAmount = newPrincipal; System.out.printf("%d, %.2f, %.2f, %.2f", paymentNumber++, monthlyInterest, monthlyPrincipalPaid, loanAmount); } } /* //method to print first payment public double getFirstPayment() { } method to print last payment public double getLastPayment() { }*/ private Person client; private int loanId; private double interestRate; private int loanLength; private double loanAmount; private static int nextId = 1; } Thanks!

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  • What are the most difficult aspects of project management in Software Engineering?

    - by Jamie Chapman
    I have been asked to provide a brief summary of the what the most difficult aspects of being a project manager of a software engineering project. However, I have no experience of this as I'm still at University and have no "hands on" experience of project management. I was hoping that someone on SO would be able to provide some insight based on their experience. What are the most difficult aspects of project management in Software Engineering?

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  • how to fix protocol violation in c#

    - by Jeremy Styers
    I have a c# "client" and a Java "server". The java server has a wsdl it serves to the client. So far it works for c# to make a request for the server to perform a soap action. My server gets the soap request executes the method and tries to return the result back to the client. When I send the response to c# however, I get "The server committed a protocol violation. Section=ResponseStatusLine". I have spent all day trying to fix this and have come up with nothing that works. If I explain what i did, this post would be very long, so I'll keep it brief. i Googled for hours and everything tells me my "response line" is correct. I tried shutting down Skype, rearranging the response line, adding things, taking things away, etc, etc. All to no avail. This is for a class assignment so no, I can not use apis to help. I must do everything manually on the server side. That means parsing by hand, creating the soap response and the http response by hand. Just thought you'd like to know that before you say to use something that does it for me. I even tried making sure my server was sending the correct header by creating a java client that "mimicked" the c# one so I could see what the server returned. However, it's returning exactly what i told it to send. I tried telling my java client to do the same thing but to an actuall running c# service, to see what a real service returns, and it returned basically the same thing. To be safe, I copied it's response and tried sending it to the c# client and it still threw the error. Can anyone help? I've tried all i can think of, including adding the useUnsafeHeaderParsing to my app config. Nothing is working though. I send it exactly what a real service sends it and it yells at me. I send it what i want and it yells. I'm sending this: "200 OK HTTP/1.0\r\n" + "Content-Length: 201\r\n" + "Cache-Control: private\r\n" + "Content-Type: text/xml; charset=utf-8\r\n\r\n";

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  • Java: Help constructing a fillTextFields() method

    - by Holly
    I have a Java project where I am to connect to a database and create buttons (next, new, save, delete, previous) to navigate through the database content where there are appropriate text fields and labels for the specific information. I'll use the code below as an example (each button is set up very similar)... I have it as follows: JButton jbtnNext = new JButton("Next ->"); jbtnNext.addActionListener(this); if (e.getSource() == jbtnNext) jbtnNext_Click(); private void jbtnNext_Click() { JOptionPane.showMessageDialog(null, "Next" ,"Button Pressed", JOptionPane.INFORMATION_MESSAGE); try { if (rset.next()) { fillTextFields(true); }else{ //Display result in a dialog box JOptionPane.showMessageDialog(null, "Not found"); } } catch (SQLException ex) { ex.printStackTrace(); } } The professor gave the following outline of logic to construct the fillTextFields() method: Construct the method to provide reusable code that would fill the JTextFields on the GUI with appropriate values from current record from the database (when "Previous or "Next" buttons are pressed) or blank values (when the new Button is pressed). To determine when the current record was to provide values (next and previous) or the value would be blank (new button) pass a boolean argument into the method. If data from the current record was to be used as fill values, pass true for both previous and next button code after moving the record pointer. If the new button was pressed and want to fill with blank values, pass false to the method. Inside the method, use a conditional expression to evaluate the boolean variable. If true, The appropriate get----() resultset method is used to fill the JTextFields. If false, fill them with "". The .setText() method of the JTextField is used to fill each JTextField. Make sure the fillTextFields method throws the appropriate exception. I understand and have the previous and next button methods passing true, while the new button method is passing false, but I don't quite understand how to set up the fillTextFields() method correctly or how to "throw the appropriate exception"... Any help would really be appreciated, thank you!

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