Agfdhyk

I have a java program that reads and iterates through each text file in a directory, makes a word index (word: which pages it appears on), and prints the output for each file into an output directory. I would like to convert this to a program that utilizes multi-threading for each file (start a new thread for each file). I am pretty new to Java and completely new to multithreading in Java. The input is:
java Index inputFolder outputFolder pageLength

Here is my working code without multi-threading:

import java.io.File;

import java.io.IOException;

import java.util.Map;

import java.util.Scanner;

import java.util.TreeMap;

import java.io.PrintStream;



public class Index {

      public static void main(String args) {

        long startTime = System.nanoTime();

        PrintStream stdout = System.out;

        try {

            File folder = new File(args[0]);

            File files = folder.listFiles();

            for (File file : files) {

              String name = file.getName();

              int pos = name.lastIndexOf(".");

              if (pos > 0) {

                  name = name.substring(0, pos);

              }

              Scanner sc;

              sc = new Scanner(file);

              Map<String, String> wordCount = new TreeMap<String, String>();

              int count = 0;

              while(sc.hasNext()) {

                  String word = sc.next();

                  word = word.trim().toLowerCase();

                  int len = word.length(); 

                  count = (int) count + len;

                  int pageNumber = (int) Math.ceil(count / Float.valueOf(args[2]));

                  if(!wordCount.containsKey(word))

                      wordCount.put(word, Integer.toString(pageNumber));

                  else

                      wordCount.put(word, wordCount.get(word) + ", " + Integer.toString(pageNumber));

              }



              // show results

              sc.close();

              PrintStream outputFile = new PrintStream(args[1]+"/"+name+"_output.txt");

              System.setOut(outputFile);

              for(String word : wordCount.keySet())

                  System.out.println(word + " " + wordCount.get(word));

            }

        }

        catch(IOException e) {

            System.out.println("Unable to read from file.");

        }

      long endTime   = System.nanoTime();

      long totalTime = endTime - startTime;

      System.setOut(stdout);

      System.out.println(totalTime / 1000000);

    }

}

To reiterate, I would like to adapt this so that each file iteration starts a new thread.

If you're using Java 1.8+ you could use the streams API.

.parallelStream() will execute the tasks in parallel, assigning a thread to each task.

You'll need a List to invoke the streams API

List<File> files = new ArrayList<>(); //initialization



//populate list here



files.parallelStream()

     .forEach(x->{

       //logic goes here

      });

Example Repl.it

Documentation about paralellism