Could Program Fail With Race Condition By Concurrent Threads In A Multi Thread Environment
Feb 18, 2014
I have a task of returning US holiday based on the given date and this utility will be used in a multi thread environment. I have written as below, how to know if my code breaks at any given point by multiple threads
Declared Enum
public enum Holiday {
CHRISTMASDAY("Christmas Day"),
GOODFRIDAY("Good Friday"),
INDEPENDENCEDAY("Independence Day"),
LABORDAY("Labor Day"),
NONE("None");
[code]...
I tried to test this with few concurrent threads, and noticed that the DB call is made for the very first time or when the year being requested is not same as the cached year. But I wanted to see, if this is properly synchronizing and would not fail in any case. My intention is to make a singleton HolidayCalendar, and also synchronized well enough so that every thread using this class gets the required data without blocking each other.
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Feb 25, 2015
I want to create off-screen images by Canvases in multi-thread environment.
I know that I use methods of GraphicsContext2D to draw on Canvas. Can I do this on Canvas which is not added to Scene ?
How can I get an image from a canvas after I invoke GraphicsContext2D methods? Can I get images in multi-thread environment ?
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Mar 24, 2014
I need a small example of an object which is visible to two different threads.
Does saying "an object is visible to two threads" mean that it's fields or methods are being used in both the threads? I am not clear about that.
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Nov 22, 2014
My task is to create multiuser console chat program. During whole day of poking around , i finally stand on such concept:
1. When running , Server part must stay into while(true) loop and create threads on each ServerSocket.accept() call, providing socket object inside thread. i.e.
while (true){
System.out.println("Waiting for client to connect");
Thread t = new Thread(new Runner(servSocket.accept(),listOfClientSockets));
System.out.println("Starting thread");
t.start();
}
2. Client side always stays within while(true) loop and waiting for user input with ScannerInstance.nextLine() method.
As soon as user prints something and hits enter, data being captured from scanner and thrown to socket output stream to the server.
My question is : if all parties (X clients and server) are actually in waiting mode (server is waiting for connections and each client is waiting for user input), who will refresh the screen for each client to draw the messages other parties sent?
At this time , each party see updates only when he hits enter and while loop does next iteration reading data from buffer and displaying on console.
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Apr 9, 2015
I created a simple Hangman game. It functions correctly, the only issue is when the file contains a phrase (2 or more words), spaces are not displayed when the program is run. For example, if the phrase was Java Programming Forums.
It would appear as _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _.
I want there to be spaces in between the words. How could I fix this? What would I need to add to my code?
import java.util.Scanner;
import java.io.*;
public class hangman{
public static void main (String[] args) throws FileNotFoundException{
Scanner kb = new Scanner(System.in);
String guess;
String guesses = "";
int wrongGuess = 8;
[Code] ....
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Feb 24, 2014
I am trying to write a program in Java that uses threads.Below is the program requirements:The goal of this assignment is to create a routine which creates multiple threads, has them do work in parallel, and terminates when the last thread has finished.
The Scenario: There are several groups of people in a bar watching the Olympics cheering for their country. Each group will cheer for their country some given number of times, with a random pause (between 2 and 5 seconds) between each cheer. There is enough room at the bar for up to ten different groups to sit (each would be cheering for a different country).
The Program: The task is to write a program that will simulate these cheers using threads. The program should be called cheer.X (X being the language of choice). You may use any language that supports threading. When the program is run it should ask for the number of countries and then the name and how many times it will be cheered for. The main function will then create a thread for each team and each thread is responsible for cheering the specified number of times for the correct team at the random interval. You will submit the proper source code file for me to open and compile myself, not an executable.
An example run would look something like this: How many countries are supported at the bar? 3 Enter the first: China How many cheers? 2 Enter the second: USA How many cheers? 4 Enter the third: Russia
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Oct 20, 2014
Create another class called Race with a main method. Make some Car objects, and use them in a race.The first race will have 2 cars. The main method only needs 2 local variables, i.e. the 2 Car objects.
-The length of the race is 1000.
-Both cars will start out with a speed of 30.
The race will be implemented as a loop. Each time through the loop:
-Your cars will move to a next location by adding their current speed to their location. (If the speed is 50, and they are at location 200, then change the location to 250.)
-Call out the race (SOPLs) like a NASCAR announcer: Andretti is in the lead at position 365. He is flying at 30 mph!
-Or It's neck and neck with both cars at position 45 or something more creative that you can come up with.
-Each car will increase or decrease their speed randomly each time through the main loop.
-The car that is behind will increase its speed by 2 mph, and the car that is in the lead will decrease its speed by 2 mph. (Tighten the race to make it more exciting.)
-The loop will continue until one of the cars is declared to be the winner.
This is my code so far.
public class RaceCarsMain {
public static void main(String[] args) {
int length = 0;
Cars c = new Cars("Andretti", 30);
Cars c2 = new Cars("Fiviotini", 30);
while (c.getLocation() < 1000){
length++;
c.randomSpeedChange();
c.accelerate(2);
c.deaccelerate(2);
c.locationchange();
[code]....
I have been able to print out the first car "Andretti" until its location reaches 1000, but the 2nd car I have not being able to print out the change of speed and change of location.how to proceed and making the 2nd car do the same, do I have to create another class? or how can i use the Cars class to do it for both.
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Oct 22, 2014
I was thinking to make a game where two cars are going to race against each other. I already have two gif pictures which are the cars. I do now have a background and a racer track. So we can start from here.
I have made a object with construction which I called Racers. Inside that, i wrote a PaintWindow (Where the window and much more is inside), -car1, -car2. All these is private. So I made something like this now:
package p2;
public class Race {
private Object window;
private Car car1;
private Car car2;
public Race(PaintWindow window, Car c1, Car c2) {
[Code] .....
But the problem is now that im kinda lost and I dont really know what to write anymore. How can I get a for example a green background on the whole PaintWindow with two Racers tracks and inside the racers tracks (Each car have each track) does it have to be cars. So I need to somehow import the cars inside it too. But thats the problem I need. that I dont really know what more to do. To make it easier, I have a Main-method in another class.
public static void main(String[] args) {
PaintWindow window = new PaintWindow();
Car c1 = new Car(new ImageIcon("C:/Users/Sarah/Desktop/CarBlue.GIF"));
Car c2 = new Car(new ImageIcon("C:Users/Sarah/Desktop/CarRed.GIF"));
Race race = new Race(window,c1,c2);
race.action();
if(args.length>0) {
Paintwindow.pause(2000);
window.dispose();
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Sep 20, 2014
I'm currently learning about Swing but I can't get my head round this piece of the code. Here is a simplified gui (not interested in the gui part but the execution)
public class SwingDemo implements ActionListener {
SwingDemo(){
JFrame jfrm = new JFrame("Simple gui pro");
//rest of code
public static void main(String[] args) {
new SwingDemo();
}
I get the above, create a new instance of SwingDemo in the main thread which starts up the gui through the constructor. However, then the tutorial says that I should avoid doing the above but do this instead:
public class SwingDemo implements ActionListener {
SwingDemo(){
JFrame jfrm = new JFrame("Simple gui pro");
//rest of code
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() { //why do this instead?
public void run(){
new SwingDemo();
}
});
}
}
Reading, it talks about an event-dispatching thread which has completely lost me... Why not just instantiate the object directly instead of creating another thread?
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Oct 17, 2014
im having an issue with the 3rd thread that are supposed to merge the two sorted sub arrays , i pass the 2 subarrays to my runnable function sortlist and they are renamed IntSortList 1 and 2 and th1.start() and th1.join() are called and it works fine, but then i have another runnable constructor that takes IntSortList 1 and 2 but it does take a runnable. below is the code in my main,
Runnable InSortlist1 = new sortList(data2p1);
Runnable InSortlist1 = new sortList(data2p1);
Thread th1 = new Thread (IntSortlist1);
Thread th2 = new Thread (IntSortlist2);
try
{
th1.start();
th1.join();
[code]....
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Aug 10, 2014
So I've been working on this program to make tournament matches for beach volley.
First little info: (I'm Belgian so some words are Dutch)
-Class Speler: has arraylist with information with which player already has been played (codesLijst)
-Class Inschrijvingen: makes players sign up with their level and name
-Class Wedstrijd: makes matches, checks with Inschrijvingen if the players already have played together. If so, gives message that they need to change partner. If not, makes them a team.
Now if I run the program with fresh players, none of them have had a partner, it works fine. If I make just one new team and the other already exists, it also works fine. It's when I make the two teams with existing records (to see whether they already played together), that the error comes.I know there's a lot of code duplicate, will clear out eventually, this is just a raw version.
CLASS SPELER
import java.util.ArrayList;
public class Speler {
private Wedstrijden wedstrijd;
private Inschrijvingen inschrijving;
private String naam, ploeg;
private int setPunten, winPunten;
private long time;
private String code;
private ArrayList<String> lijstCodes = new ArrayList<String>();
[code]....
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Dec 17, 2014
My program is user input 20 char and the program will print the most common. So I use another int arr which count the number appears in the original array. i know its not so Effective but I don't know why it run but it stop in the middle. I got this code :
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 20
at Ex2.common(Ex2.java:39)
at Ex2.main(Ex2.java:23)
import java.util.Scanner;
class Ex2 {
public static void main(String[] arg) {
Scanner reader = new Scanner (System.in);
char[] arr=new char[20];
System.out.println("Please enter 20 chars:");
for (int i=0;i<20;i++)
[Code] ....
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Jul 8, 2014
I have inherited some code that is supposed to work just fine. The trouble is that when everything is rebuilt on my desktop, the projects crash. They all seem to crash at one particular part of code.
I pass it a string and the "getResource" or "getContentClassLoader" is failing.
[URL] ....
I guess one way to tackle this is to break it apart into segments.
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Jul 9, 2014
I have inherited some code that is supposed to work just fine.
The trouble is that when everything is rebuilt on my desktop, the projects crash.
They all seem to crash at one particular part of code.
I pass it a string and the "getResource" or "getContentClassLoader" is failing.
[URL] ....
I guess one way to tackle this is to break it apart into segments.
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Jul 8, 2014
I have inherited some code that is supposed to work just fine. The trouble is that when everything is rebuilt on my desktop, the projects crash. They all seem to crash at one particular part of code. I pass it a string and the "getResource" or "getContentClassLoader" is failing.
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Mar 27, 2014
My code is like this,
for(Iterator iterator = list.iterator(); iterator.hasNext();) {
String string = iterator.next().toString();
list.add(string + "Hello");
iterator.remove();
}
Its a simple program. I've list with some names as values like,
Ram, Sham, Bham, Bhim, Suraj.
Now, I want to add "Hello" to each name by running above code. While iterating, first time I get Ram, I want to add "Hello" to Ram and add to list as "Ram Hello" also I want to remove original Value i.e "Ram". When I run above code it is giving Concurrent Modification Exception. How to do this?
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Jul 16, 2014
class A extends Thread
{
String str;
public void run( )
{
//random stuff
}
}
[Code]....
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Feb 13, 2014
What I am attempting to do is execute a long-running process and iterate over it multiple times. I'd like my page to update with the progress in between each run. What I have tried so far is using a HttpSessionAttributeListener and executing my long-running process from there and using my ViewScoped bean along with richfaces a4j:poll to update my page. Unfortunately no matter what method I try with a listener, the completion of the Partial JSF lifecycle always blocks until my listener method is through processing. So we go from start to finish with no updates in between.
I have which is to just have my view re-submit itself and try updates that way. But before I go that route I wanted to see if there was a way to do what I was originally attempting and I'm not just missing something.
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Feb 8, 2015
As part of a homework assignment in my 1st Java Class, I am creating my own Circular Generic LinkedList and Array class. My class uses the Queue Interface Extends Iterable but I am creating my own methods to work with. For the most part, I believe I have been successful in creating the class aside from one method. That method is the Iterator<E> iterator().
/**
* Return a fail-fast iterator, which throw a java.util.ConcurrentModificationException
* if the client modifies the collection (via enqueue(...) or dequeue()) during iteration.
*/
@Override
public Iterator<E> iterator() {
I don't understand how an iterator, let alone a "fail-fast" iterator ties into my project. I've spent hours reading up on a way to imploy my own generic fail-fast iterator but to no avail.
I feel like I could come up with some workable code if I knew what the point is to useing a user-defined, non Java Library iterator is to do.
As well, does throwing a ConcurrentModificationException require a try and catch block?
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Apr 7, 2014
I'm writing an IRC server in Java, however when a client tries to connect I get a ConcurrentModificationException trying to add them to an ArrayList. My code is Here: [URL]
I don't understand why I am getting a ConcurrentModificationException or what one is.
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Aug 13, 2014
Using Java 7 update 5 (I know it's old...), we are trying to send concurrent requests to a RMI Server. When we start to tamp up the load (not too much - up to 50 concurrent requests) we start to see many IO Problems like Broken Pipe and Connection Reset By Peer. Could we be hitting some unknown limitation on concurrent access? Is there such limitation?
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Aug 13, 2014
I'm writing a simple program in which I have a super class Person, inherited by the subclasses Customer and Employee (they inherit the variables ID, name and surname).
Java Code:
public class Person {
int id;
String name;
String surname;
public Person () {
[Code] .....
However the problem is here: when I try to get the variables ID, name and surname through my main class, they fail to return (0,null,null). Why is this? I have get-Methods in my subclasses which should return the super variables, but they are not.
Java Code:
public String getUser() {
return username;
}
public String getName() {
return super.name;
} mh_sh_highlight_all('java');
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Apr 13, 2014
I am new in this programming language, java. I have a problem after I set my path ";C:Program Files (x86)Javajdk1.7.0_51in". I made a simple program but an error occurred. Here's the screenshot.....
Attached image(s)
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Jul 18, 2014
Can we use EJB @Asynchronous annotation in distribute environment. I know we can use it but I want to know its Advisable or not. Because It's not advisable to manage user thread in Distribute environment like EJB container .Earlier if we want to make Asyn call then we use JMS. But now they added @Asynchronous annotation with Future Class to achieve the same result.
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Oct 8, 2014
I have a project which has a set of configuration files, where each configuration file represents an environment specific configurations. In other words, I have 3 environments, development, staging, and production. The configuration for each environment is different, e.g. DB name, url etc.
Whenever I want to deploy the same code, on each environment, I have to manually generate environment specific .war file, so that it has environment specific configuration file in it.
What I am looking for is a kind of solution where i have to compile only once in maven and it generates only one .war file, which I can use on every environment. In other words, i want the environment specifi application server/tomcat to identify which configuration to pick.
That way, I'll be sure that we are deploying and testing the same .war file on every environment/application server.
How can i restructure the application to achieve this functionality?
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Oct 8, 2014
How to access one thread from another thread?
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