Handling IO Synchronization
Sep 16, 2014
I have a class (WriteExcel) which writes to an excel file. For those who don't know, Excel doesn't handle multiple access well (or at all).
I then have another class (WriteManager) which creates a new thread for each write command, and then calls a method from the WriteExcel class.
Other classes in my project calls methods from WriteManager to send their requests. My situation looks like this:
1) Thread 1: Someclass -> WriteManager.write1stPage(write) -> Creates Thread 2 -> WriteExcel.write1stPage(write) -> Start Excel Write
2) Thread 1: Someclass -> WriteManager.write2ndPage(write) -> Creates Thread 3 -> WriteExcel.write2ndPage(write) -> Start Excel Write
3) Thread 1: Someclass -> WriteManager.write3rdPage(write) -> Creates Thread 4 -> WriteExcel.write3rdPage(write) -> Start Excel Write
4) Thread 2: Finished writing and ready to save -> Throws exception due to multiple Excel access
5) Thread 3: Finished writing and ready to save -> Throws exception due to multiple Excel access
6) Thread 4: Finished writing and ready to save -> Throws exception due to multiple Excel access
I need to figure out a way to restrict access to WriteExcel until the writing is finished. So I need something like this:
1) Thread 1: Someclass -> WriteManager.write1stPage(write) -> Creates Thread 2 -> WriteExcel.write1stPage(write) -> Start Excel Write
2) Thread 1: Someclass -> WriteManager.write2ndPage(write) -> Creates Thread 3 -> Waits Until WriteExcel is free
3) Thread 1: Someclass -> WriteManager.write3rdPage(write) -> Creates Thread 4 -> Waits Until WriteExcel is free
4) Thread 2: Finished writing and ready to save -> Saves and frees WriteExcel
5) Thread 3: WriteExcel is free -> WriteExcel.write2ndPage(write) -> Start Excel Write
6) Thread 3: Finished writing and ready to save -> Saves and frees WriteExcel
7) Thread 4: WriteExcel is free -> WriteExcel.write3rdPage(write) -> Start Excel Write
8) Thread 4: Finished writing and ready to save -> Saves and frees WriteExcel
What is currently the best approach in java for handling this sort of situation?
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Mar 7, 2014
I have studied about the hierarchy of exception classes in which Throwable class comes at the top and two of its direct subclasses are Error and Exception..I just want to ask if in some code snippet we throw an instance of Error or its subclass within the try catch block then will that be also called "exception handling" ? I am asking this because Error class is not a child class of Exception therefore cant be said an Exception, therefore handling the same should not be called exception handling
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Feb 19, 2015
I have no clear idea about Synchronization..What is main purpose of it and where it is useful in realtime.
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May 27, 2014
There is method in the class of my application and there are four other class which is running in different machine means different jvm and these classes are accessing the method of my class. then how to protect my method from accessing other class at the same time. I am not able to use synchronized keyword because this works only for single jvm.
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Apr 28, 2014
I created a GUI using Java with Buttons, Pictures and labels.When one of the buttons is pressed it increases the price, which can be seen by the labels increasing the necessary amount.What I would like to be able to do in my GUI is allow the user to record details of the sale and be able to display the sales of past customers to date, by this I mean when I click one of the buttons it will record the amount of that item into a file and when I press the another button, not the same button as the items, it will show the user the existing orders that have been taken in the past.
Here is my Code:
//Importing needed classes
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
[code]....
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Aug 17, 2014
Is there any connection between packages and exception handling in java. Means is it necessary to create a package before trying exception handling examples?
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Apr 22, 2014
Is there a special mechanism through which exception can be handled in a constructor?
Suppose while creation of an object there occurred an exception while creating an object, and the object is half constructed. How do we make sure we handle this kind of exceptions in a constructor?
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Sep 16, 2014
The game I am working on now is an overhead game. Anyways I have a visual issues with the sprites where they overlap. I mean its normal to have sprites overlap but I do not want one to appear like it is walking on top of the other rather than the ground. The below is an image illustration the issue I want to address. (I am really good at drawing)
On the right you see what I want my sprites to do, but on left you see overlap in the way I am trying to avoid.
Now my approach to this problem is taking my array of monsters (a class that extends JLabels) and reordering them based on which monster is higher I make this occur at every run of my thread. It seems to me that if a monster is higher it should be added to the screen before the one that is lower. So I try to keep resorting the array of monsters at every iteration of my main game loop based on who is higher to account for the overlap
if (e.getSource() == follower){
c =0;
for (monster m: monsters) {
//Arrays.sort(monsters, new whoHigherComparator()); //I tried having the sort happen here
m.movingToPlayer(joe);//1
Arrays.sort(monsters, new whoHigherComparator());//2
layeredScene1.add(m, new Integer(3));//3
[code]...
The above is code that shows the majority of my games flow I will describe my flow with references to the commented lines above with [num] for better understanding of where I am coming from. Basically, there is a set number of monsters, the monster all locate and move to the player [1], then I attempt to sort the monster array based on height [2], then add my re-sorted monsters back onto the pane in order [3], then bumpers (a type that handle collision and make sure monsters don't overlap too much) attach the current monster [4], if bumpers are touching monsters arae moved away from each other until their bumpers are no longer touching [5], if the monster is moving leftwards set the animation to a leftwards walk [6], and likewise for rightwards walking [7]
By the way this is my comparator
public class whoHigherComparator implements Comparator<monster>
{
@Override
public int compare(monster m1, monster m2) {
System.out.println("comping?");
int h1 = m1.getY();
int h2 = m2.getY();
if (h1 < h2)
[code]...
At this point everything in my game flow works just fine, its just the annoying "walking on top of each other" effect that I am having trouble handling. And my attempt at this is line [2] & [3] from my game flow which seems like it would be an effective way to handle the "walking on top of another" effect but its surely not working. I also swapped the returns from my comparator but still no changes. It seems that maybe the array isn't being sorted and/or these changes are just not being reflected.
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Oct 31, 2014
I found an exercise online to create a small program . I have this code that I have done so far:
import java.util.Scanner;
public class Test {
public static void main(String args[]) {
Scanner sc = new Scanner(System.in);
long a = sc.nextLong(); long b = sc.nextLong();
long count = 0; // counter
[code]....
The program should read the numbers a and b and list how many numbers between a and b are divisible by either 2, 3 or 5. If the user types the number 5 and then 8.... it would look at all the numbers in between - 5,6,7,8 and check if any of them are divasable by either 2,3 or 5. And since the numbers 5,6,8 are it would return the number 3 to the user..Now the problem is that this program only works for small numbers, but when I try to input numbers such as 123456789012345678 and 876543210987654321... it doesn't run at all.
So there needs to be a quicker way on how the program checks the numbers divisibility instead of checking each one. Here is where I am lost. How to fix the program that it will read bigger numbers such as a=123456789012345678 b=87654321098765432..There must be a quicker way ...something that can modify the code so it finishes in the matter of seconds not hours. Something that will fasten the process of checking if the numbers are dividable.
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Nov 25, 2014
For one of my last labs for the semester, my professor is having the class go back to our very first program and apply some of the exception handling that we just recently learned about. Here's my improved code so far:
Java Code: import java.util.*;
import java.lang.*;
public class Lab2Part1 {
public static void main (String [] args) {
Scanner input = new Scanner (System.in);
[code]....
My code compiles fine, but even if I enter an integer or a double, it saves the number as a string, and prints that out as the name. Is there any way to get around this? Or do I need to use something besides a try-catch?
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Feb 19, 2014
On click of the ok button from a JSF page, a servlet is called on a new window. Servlet creates a CSV file , which will be streamed back for a download. Now if there is a error in the servlet, how can this be shown in the parent JSF?
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Apr 19, 2015
I have been working on a problem dealing with exception handling and text input output for a few days now. The exercise is a two part exercise. The first part of the exercise I have to write a program to display the total salary for assistant professors, associate professors, full professors, and all faculty, respectively, and display the average salary for assistant professors, associate professors, full professors, and all faculty, respectfully using the what is posted on the [URL] .... Each line in the file consists of a faculty member's first name, last name, rank, and salary. The second part of the exercise I have to take my code and change it so that it
-lets the user enter the name of the file to be read,
-Uses a try-catch block to handle the FileNotFoundException displaying instead The file already exists..
... Use a second catch block to ignore any other exception thrown.
... Design your code so that, if the user enters a file that does not exist, the program prompts the user to enter again a file name.
and I need to Note: In order to catch the FileNotFoundException, you need to include import
java.io.FileNotFoundException;
package pkg14.pkg25;
import java.util.Scanner;
import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;
[code]...
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Mar 31, 2015
I have done this a few times but I want to make sure I am doing it correctly. In other words creating a clean understandable program. Instead of posting code I will just talk about this is my plan:
Create a model (getter and setters)
Create a view (via swing)
Create a controller (pass the model and view in the parameter)
Database DatabaseConnection:
Use the singleton pattern
Database:
Create an interface called Database with all the queries I will need (insert, delete etc)
Create a class called DataBaseDAO and implement the interface database and get an instance of the DatabaseConnection.
Tying it all together:
In the controller should I use the "new" operator and create a new database class or extend the database class? I am thinking I should not do it in the controllers constructor but make a field if I use the "new" operator like:
private Database db = new Database();
Create a class called App
Create a new Model
Create a new View
Pass the view and model into the controllers parameter.
Am I on the right track? Is this messy? Is there a better way of doing it?
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Aug 20, 2014
Assume we have 2 files that are input.txt and output.txt Input.txt has Name||Age||email||contact No||Name1||age1||email1||contact No1||name2||Age2||email2||contact no2||etc...
initially the output.txt does not have any record.using a java program we have to make it as
Names in the input file:Name,Name1,Name2,Name3 Ages in the input file:Age,Age1,Age2,Age3 email id in the file: email, email1, email2 Contact no in the file:contact no, contact no1,contact no2
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Feb 10, 2014
I have a GUI that prompts the user for information. When they click 'submit', a new customer gets created from a class like so ...
Java Code:
public void actionPerformed(ActionEvent arg0) {
Customer customer = new Customer(); // New customer object
customer.name = view.getName();
customer.age = Integer.parseInt(view.getAge());
customer.ccn = view.getCCNumber(); mh_sh_highlight_all('java');
I am having difficulties validating my variables for nulls. For instance ...
Java Code:
// METHOD TO RETRIEVE TEXTBOX INPUT -- NAME
public String getName() {
String name = null;
if (jtfFirstName.getText() == null || jtfLastName.getText() == null || !jtfFirstName.getText().matches("[a-zA-Z]+") || jtfLastName.getText().matches("[a-zA-Z]+")){ // Validate name fields
JOptionPane.showMessageDialog(null, "<html><i>Improper Input Detected.</i>
[code]...
I can't seem to win with this. Whether the fields are filled in properly or not, I get the error message and the program continues to completion using the name "null".
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Dec 9, 2014
I am calculating an exponent without using BigInteger. However, I find that using long is not enough to handle my code. Is there a way to handle large numbers without using BigInteger?
public static void main (String[] args){
int base = 3;
int exponent;
long total = 1L;
boolean n;
Scanner input = new Scanner(System.in);
[code].....
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May 8, 2014
I'm making a program that finds the maximum, minimum, and average values in an integer input ended with a negative number. For example, 4 5 6 -1 is min:4, max:6, and average:5.
It's supposed to handle faulty input in two situations:
1.When an input other than integers is given, the user is given a second chance to give a proper input.
2.When no numbers are given (which is only possible by giving nothing but the negative number end mark), an error message is given because diving by zero integers is impossible.
All the math works fine, but for some reason a proper input in the second chance doesn't. Failing the second chance works, and giving proper input all the way through works. If I fail the first input and then give a proper integer input on the second chance, the program skips over the calculation and gives the divide by zero error. All I could understand from the debugger is that the program is recognizing whatever the first number in that input is, but still keeps the number of numbers as zero (so it's not looping to compare all the numbers in the line either).
import java.util.Scanner;
public class FindNumbers implements FindNumbersInterface
{
double average;
double sum;
int numberOfNumbers;
int total;
[Code] .....
I have a few bits of //old stuff that I've been keeping in case I want to go back.
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Jun 17, 2014
I want to use my given code as base class
Java Code:
public static void file(String[] arg) throws IOException{
BufferedReader in;
String line;
try{
System.out.println("Reading word");
in =new BufferedReader(new FileReader("inp.txt"));
[Code] .....
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Mar 3, 2014
I am new at JSF and i want to do some things.
->When the user request for a file that is not exists i want to redirect to a valid url where i can inform him that the file does not exists.
->I am trying to use the properties messages for the language that the user has. I want to use it cause i want to reuse some of the message and it is easier to translate the page to other languages. How when the browser has a default page English to let user change the language to Italian for example but for all page.
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Dec 20, 2014
I'm doing this assignment in which i have to write some products in csv file...but as u can see in csv file two products are same "Cooking Oil"..so any method that can add two same product's quantity and their amount and write them in file
import java.util.*;
import java.io.*;
public class SalesbyTransactionMonth{
private static final String fileName = "Data.txt";
private static final String fileName1 = "sales_by_trans_month.csv";
String line = "";
[Code] ....
Attached image(s)
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Jun 19, 2014
I know I can calculate the sum of squares as such:
// SumSquares.java: calculate the sum of two squares
class SumSquares {
static int sumSquares(int a, int B)/>/> {
int asquare;
int bsquare;
[Code] ....
But how can I modify the code so that it inputs a list of integer values in the range of -100 to 100 from the keyboard and computes the sum of the squares input values. And how would I go about using exception handling to ensure that the input values are in range and are legal integers.
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Nov 6, 2014
I am supposed to make a code which can handle fractions as a calculator in the form of 1_1/2 + 1 = 2_1/2
This is what I've done so far and now im just lost.
Heres my code:
import java.util.Scanner;
import java.util.StringTokenizer;
public class FracCalc {
public static void main(String[] args ){
// read in the first expression
[Code] ....
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Apr 13, 2015
Now I have a problem for file handling it is not store bytes in to rahul.txt. it stores character not bytes.
package com.fileh;
import java .io.*;
//import java.io.File;
public class Writedata {
public static void main(String args[])
{
try{
FileOutputStream fout= new FileOutputStream("rahul.txt");
String s="my name is rahul";
byte[] b =s.getBytes();
fout.write(b);
fout.close();
}
catch(IOException ioe)
{
}
}
}
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Jan 28, 2014
In our J2EE web application we have so many critical functionality which is handled by various component. Say if one of the critical object or the respective critical system is down. How we can serve the request and still get the response from those systems? How this can be handled technically through code? I know we can go for service virtualization and create a system which will emulate the behavior of critical object or system. But for that we need to use the respective tools which is quite costly. How the same can be handled using java code , whether we can create a clone of that critical object and still serve the request even though the original critical object is down or can we create a proxy of that critical object? How we can handle it in java through code?
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Mar 12, 2015
How to modify a specific line of a file in java. File name must be accepted from command line.
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Oct 18, 2014
The requirement is to write a rectangle class and a test class, which include try-catch blocks and exception handling. Exceptions, involving try, catch, throw, throws, and finally commands,how to write a code about basic things, but in the test class, it gives me specific width and height so that i dont konw how to write a try-catch blocks an exception handling in this test class.There is my two classes, they are separated.
public class Rectangle {
double width ;
double height ;
Rectangle(){
width = 1;
height = 1;
[code]....
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