Help, please.

Question about the task

Under discussion

I am trying to solve this task but program cannot finish normal way - after result id displayed, it need additional inputs to close reader and Exception is thrown in one of threads. Can you give me some hint?

1. Figure out what the program does.
1.1. Each thread should read lines from the console. Use the existing static BufferedReader reader.
1.2. Use AtomicInteger readStringCount to calculate how many lines all the threads have read from the console.
2. Implement the run method:
2.1. As long as a thread is not interrupted (!IsInterrupted), read lines from the console and add them to List<String> result.
2.2. Use readStringCount to count the strings read from the console.

Requirements:

The run method must run until the thread is terminated (!IsInterrupted).
The run method must NOT create its own InputStreamReaders or BufferedReaders.
The run method must read words from the reader and add them to the result list.
After each string is read, the run method must increment readStringCount by 1.
The program should display the data read by each thread.

package com.codegym.task.task16.task1628; import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; import java.util.ArrayList; import java.util.List; import java.util.concurrent.atomic.AtomicInteger; public class Solution { public static volatile AtomicInteger readStringCount = new AtomicInteger(0); public static volatile BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); public static void main(String[] args) throws IOException { // Read string count int count = Integer.parseInt(reader.readLine()); // Init threads ą ReaderThread consoleReader1 = new ReaderThread(); ReaderThread consoleReader2 = new ReaderThread(); ReaderThread consoleReader3 = new ReaderThread(); consoleReader1.start(); consoleReader2.start(); consoleReader3.start(); while (count > readStringCount.get()) { } consoleReader1.interrupt(); consoleReader2.interrupt(); consoleReader3.interrupt(); System.out.println("#1:" + consoleReader1); System.out.println("#2:" + consoleReader2); System.out.println("#3:" + consoleReader3); reader.close(); } public static class ReaderThread extends Thread { private List<String> result = new ArrayList<>(); public void run() { //write your code here while (!isInterrupted()) { String alpha = ""; try { alpha = reader.readLine(); } catch (IOException e) { e.printStackTrace(); } result.add(alpha); readStringCount.incrementAndGet(); } } @Override public String toString() { return result.toString(); } } }

Comments (7)

Popular
New
Old

You must be signed in to leave a comment

Rich

Level 23 , San Diego, United States

20 January 2021, 05:46

check for null before adding

Guadalupe Gagnon

Level 37 , Tampa, United States

3 January 2019, 18:57

this is what passed for me in the run() method:

while (!isInterrupted()){
               try{
                   String line = reader.readLine();
                   if (line != null) {

                       result.add(line);
                       readStringCount.incrementAndGet();
                   }
               } catch (IOException e){}
           }

+24

Ahmed

Level 23 , Amsterdam, Netherlands

28 June 2019, 08:24

your solution works... thanks for that! However my solution was almost the same expect of the (if) statement. I think this excursus makes no sense!!

ilian44

Level 30 , Veliko Turnovo, Bulgaria

14 November 2019, 13:14

yes, only because one senseless if() statement? what's going on here? p.s. Guadalupe Gagnon thanks

Guadalupe Gagnon

Level 37 , Tampa, United States

14 November 2019, 14:59

It is important to remember that bufferedReader can also be set up to read directly from a file and what happens in the testing of code is that codegym takes the "System.in" that we use in the code and replaces it with a file that has data. This is so someone at codegym doesn't have to manually input data in everytime a student hits verify. When a file is the target location of the BufferedReader, and the readline() method is called past the point that all the data has been read in, BufferedReader returns null. This code is going to continue to call the readline() method infinitely until the thread is interrupted, which in today's computer systems happens literally thousands a times a second. So the if check before in this code is to ensure that the counter is only incremented (and data is added to the list) when valid has been read in. If you want a demonstration copy and paste this code into intelliJ, or whatever IDE you use, and run it:

public static void main(String[] args) throws IOException {
   // ↓ set this line to a test file on your computer with some
   // random lines inside of it
   String filename = "C:\\Users\\lupeh\\Desktop\\temp\\Armstrong.txt";
   try(BufferedReader r = new BufferedReader(new FileReader(filename))) {
      int counter=1;
      for (;;counter++) {
         System.out.println(counter + " : " +r.readLine());
      }
   }
}

Run it and then hit the stop button after a second of so. The counter reads 16490 on my computer when i hit stop directly after it starts.

+11

Robert Constantinescu

Level 25 , Bucharest, Romania

28 November 2019, 17:58

i also had a simillar solution that remaine for 1 or 2 lines hanged, and i wonderd why it did not passed, even though this one pass and still hangs a little bit in the end

Daniel Walbolt

Level 22 , Waterville, United States

11 July 2020, 05:40

I mean, you can even personally test the code prior to adding the if(null) check. After the console displays the result, you can still type 3 lines in, because 3 threads are still waiting for a line to be input. I noticed this but didn't understand how it's verified, so I went to the help section lol. Thanks!