Different Approaches to Concurrent Programming in Java

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

/**
* @author evivehealth on 08/02/19.
*/
// Java program depicting 
// concurrent programming in action.

// Runnable Class that defines the logic
// of run method of runnable interface
public class Counter implements Runnable 
{
    private final MainApp mainApp;
    private final int loopLimit;
    private final String task;

    // Constructor to get a reference to the main class
    public Counter
          (MainApp mainApp, int loopLimit, String task)
    {
        this.mainApp = mainApp;
        this.loopLimit = loopLimit;
        this.task = task;
    }

    // Prints the thread name, task number and 
    // the value of counter
    // Calls pause method to allow multithreading to occur
    @Override
    public void run()
    {
        for (int i = 0; i < loopLimit; i++) 
        {
            System.out.println("Thread: " +
            Thread.currentThread().getName() + " Counter: "
                             + (i + 1) + " Task: " + task);
            mainApp.pause(Math.random());
        }
    }
}
class MainApp 
{

    // Starts the threads. Pool size 2 means at any time
    // there can only be two simultaneous threads
    public void startThread()
    {
        ExecutorService taskList = 
                         Executors.newFixedThreadPool(2);
        for (int i = 0; i < 5; i++) 
        {
            // Makes tasks available for execution.
            // At the appropriate time, calls run 
            // method of runnable interface
            taskList.execute(new Counter(this, i + 1,
                                    "task " + (i + 1)));
        }

        // Shuts the thread that's watching to see if 
        // you have added new tasks.
        taskList.shutdown();
    }

    // Pauses execution for a moment
    // so that system switches back and forth
    public void pause(double seconds)
    {
        try 
        {
            Thread.sleep(Math.round(1000.0 * seconds));
        }
        catch (InterruptedException e)
        {
            e.printStackTrace();
        }
    }

    // Driver method
    public static void main(String[] args)
    {
        new MainApp().startThread();
    }
}