How to evaluate the performance of a simple java program?

Question

Suppose I have a function that do some operation for me. Let's call it operation(). I run this operation() function in a loop for ever in another thread

My question is how can I precisely (as much as possible) compute the throughput of executing operation function. In other word, I want to know how many times this function executes in say a millisecond?

This is my implementation:

MainClass.java

import java.util.ArrayList;
import java.util.concurrent.atomic.AtomicInteger;

public class MainClass {

    static int numOfIterations = 100;

    static AtomicInteger numOfOperationsDone = new AtomicInteger(0);
    static ArrayList<Long> clientOperationTimes = new ArrayList<>();
    static ClientThread[] clientThreads; 
    static int numOfClients = 1;

    static long timeBeforeExp = 1000;
    static long expDuration = 3000;

    static boolean record = false; 
    static boolean stop = false;

    public static void main(String[] args) throws InterruptedException {
        clientThreads = new ClientThread[numOfClients];
        Thread[] threads = new Thread[numOfClients];
        for (int i=0; i< numOfClients; i++){
            clientThreads[i] = new ClientThread();
            Thread t = new Thread(clientThreads[i]);
            threads[i] = t; 
        }
        for (int i=0; i< numOfClients; i++){
            threads[i].start();
        }

        Thread.sleep(timeBeforeExp);

        record = true;


        long start = System.nanoTime();
        Thread.sleep(expDuration);
        stop = true;
        record = false;

        long elapsed = System.nanoTime() - start; 

        System.out.println("Actual elapsed time= " + Math.pow(10, -6) * elapsed);

        double throughput = Math.pow(10, 6)*numOfOperationsDone.longValue() / (double)elapsed;  
        System.out.println("Throughput= " + throughput);

    }

}

ClientThread.java

  public class ClientThread implements Runnable{

    public void run(){
        while (!MainClass.stop)
            operation();
    }

    void operation(){
        Utils.waistTimeHaha(MainClass.numOfIterations);
        if (MainClass.record) MainClass.numOfOperationsDone.incrementAndGet();
    }
}

Is it the way you would do it?

Thanks