How to measure time taken by a function in java ?

// Java Program to demonstrate use
// of System.nanoTime() method
import java.io.*;

// Driver class
public class ExecutionTimeExample {
    // main function
    public static void main(String[] args)
    {
        // Start measuring execution time
        long startTime = System.nanoTime();

        count_function(10000000);

        // Stop measuring execution time
        long endTime = System.nanoTime();

        // Calculate the execution time in milliseconds
        long executionTime
            = (endTime - startTime) / 1000000;

        System.out.println("Counting to 10000000 takes "
                           + executionTime + "ms");
    }
  
    // A dummy function that runs a loop x times
    public static void count_function(long x)
    {
        System.out.println("Loop starts");
        for (long i = 0; i < x; i++)
            ;
        System.out.println("Loop ends");
    }
}

// Java Program to demonstrate use
// of System.currentTimeMillis() method
import java.io.*;

// Driver Class
public class Time {
    // main function
    public static void main(String[] args)
    {
        // starting time
        long start = System.currentTimeMillis();
    
        // start of function

        count_function(10000000);

        // end of function

        // ending time
        long end = System.currentTimeMillis();
        System.out.println("Counting to 10000000 takes " +
                                    (end - start) + "ms");
    }

    // A dummy function that runs a loop x times
    public static void count_function(long x)
    {
        System.out.println("Loop starts");
        for (long i = 0; i < x; i++)
            ;
        System.out.println("Loop ends");
    }
}