Hi, whats wrong with my code?

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Hi, whats wrong with my code, it works fine but it is not getting verified. When I run it, the output is fine however the program does not terminate, could someone help ?

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; /* 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: 1. The run method must run until the thread is terminated (!IsInterrupted). 2. The run method must NOT create its own InputStreamReaders or BufferedReaders. 3. The run method must read words from the reader and add them to the result list. 4. After each string is read, the run method must increment readStringCount by 1. 5. The program should display the data read by each thread. */ 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 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() { while (!Thread.currentThread().isInterrupted()){ try { result.add(reader.readLine()); readStringCount.getAndAdd(1); } catch (IOException e) { e.printStackTrace(); } } } @Override public String toString() { return result.toString(); } } }

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Guadalupe Gagnon

Level 37 , Tampa, United States

17 March 2021, 16:13

interrupt() does not stop a thread, so any thread still waiting for user input at line 62 will not end until it receives user input and then the while loop breaks. The problem with this code is that null String values are not being considered in the run method. Make sure to only add a Sting to result and increment the AtomicInteger if the String is not null.

Guadalupe Gagnon

Level 37 , Tampa, United States

17 March 2021, 16:24

When you don't have control over the input stream, you have to assume that null values could come through. For example, use this test code on a file on your computer (enter your file where it specifies):

public static void main(String[] args) throws Exception {
    FileReader fis = new FileReader("ENTER_YOUR_FILE_HERE");
    BufferedReader reader = new BufferedReader(fis);

    for (int i = 0; i < 100; i++)
        System.out.println(reader.readLine());
}

If your file has over 100 lines in it to read, then this code will output the first hundred lines. If it has less than 100 lines then it will output all the lines it has, then "null" until the loop finishes. This is what can happen in your code when the InputStream, which you don't control, is changed to a file.

Mina Nabil

Level 17 , Sydney, Australia

17 March 2021, 16:50

Thanks for the answer Guadalupe, but regarding the run() method public void run() { while (!Thread.currentThread().isInterrupted()){ try { result.add(reader.readLine()); readStringCount.getAndAdd(1); } catch (IOException e) { e.printStackTrace(); } } } why it will not stop the thread ? With stop I mean exit the child thread. !Thread.currentThread().isInterrupted() will be false, so the loop will exit, so why it is not exiting

Guadalupe Gagnon

Level 37 , Tampa, United States

17 March 2021, 16:52

the code will be waiting for user input, like i said above. It won't reach the point of breaking the loop until the user input line is satisfied.

Guadalupe Gagnon

Level 37 , Tampa, United States

17 March 2021, 16:55

There are three threads here. When you enter user input for one, it will increase the AtomicInteger by one. This means that at a certain input the AtomicIntger is going to reach the point of "count" and all three threads will have interrupt() called; but 2 threads are still going to be waiting for user input.