I can't find a solutions. I have tried all methods to check if the thread has started.

Question about the task

Sequential file output

Java Core, Level 6, Lesson 13

Resolved

1. Figure out what the program does.
2. In a static block, read 2 filenames: firstFileName and secondFileName.
3. Inside the Solution class, create a public static ReadFileThread class that implements the ReadFileInterface interface (Think about what is more appropriate: Thread or Runnable).
3.1. The setFileName method must set the name of the file whose contents will be read.
3.2. The getFileContents method must return the contents of the file.
3.3. In the run method, read the contents of the file and close the stream. Separate the lines of the file with spaces.
4. Think about where you need to wait for the thread to finish to ensure that the files are displayed sequentially.
4.1. To do this, add a call to the appropriate method.

Expected output:
[entire contents of the first file] [entire contents of the second file]

Requirements:

The Solution class's static block should read from the console the names of two files and store them in the variables firstFileName and secondFileName.
In the Solution class, declare the public static ReadFileThread class.
The ReadFileThread class must implement the ReadFileInterface interface.
The ReadFileThread class must inherit the appropriate class.
The ReadFileThread class's run method should read lines from the file set by the setFileName method. And the getFileContents method of this same class must return the file contents. The return value is one string consisting of the lines of the file, separated by spaces.
The systemOutPrintln method must call the join method on the created object f.
The program's output should consist of 2 lines. Each line contains the contents of one file.

package com.codegym.task.task16.task1630; import java.io.*; public class Solution { public static String firstFileName; public static String secondFileName; //write your code here static { try { BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); firstFileName = reader.readLine(); secondFileName = reader.readLine(); reader.close(); } catch(IOException e) { e.printStackTrace(); } } public static void main(String[] args) throws InterruptedException { systemOutPrintln(firstFileName); systemOutPrintln(secondFileName); } public static void systemOutPrintln(String fileName) throws InterruptedException { ReadFileInterface f = new ReadFileThread(); f.setFileName(fileName); f.start(); //write your code here f.join(); System.out.println(f.getFileContents()); } public interface ReadFileInterface { void setFileName(String fullFileName); String getFileContents(); void join() throws InterruptedException; void start(); } //write your code here public static class ReadFileThread extends Thread implements ReadFileInterface { String fileName; String fileContent = " "; @Override public void setFileName(String fullFileName) { this.fileName = fullFileName; } @Override public String getFileContents() { if(this.isAlive()) { return fileContent; } else { return " "; } } @Override public void run() { try { FileReader fr = new FileReader(fileName); BufferedReader bufer = new BufferedReader(fr); String cadena; StringBuffer sb = new StringBuffer(); while ((cadena = bufer.readLine()) != null) { sb.append(cadena); sb.append(" "); } fileContent = sb.toString(); bufer.close(); } catch(FileNotFoundException e) { e.printStackTrace(); } catch(IOException e) { e.printStackTrace(); } } } }

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Thomas

Level 41 , Bayreuth, Germany

8 October 2023, 21:19

solution

When you start a thread, then it runs independently of the main thread. However here you have the requirement that threads should run sequentially. Means, the main thread uses join and waits till a spawned thread is finished. And when it is finished, then the main thread resumes, knowing that the thread it was waiting for has finished. No need to check anymore if that's true. So after the join, when the threads run method is done, execution in main continues. The thread has stopped but the object is still alive. Garbage collection hasn't cleaned it up as there is still a reference to it. That again means you can invoke all methods of the ReadFileThread object. You just can not start the thread a second time. So it is enough to just return the fileContent in the getFileContents() method. Not sure if a trailing space is allowed. Eventually you need to remove that (or take care it doesn't get created in the first place). When the file is empty you return a space (or two if you count the trailing space). That's not asked and you should remove that. just to mention it: StringBuilder will do, too. Doesn't need to be thread safe as it is not a shared resource.