CODEWITHSUNDEEP
javacollections
Prabha
Prabha

Reputation: 705

How to calculate the execution time of a Loop for one iteration?

Below is My code:

public class FindTime {

HashSet<String> hashSet = new HashSet<>();

long m1() {
    hashSet.add("hai");
    hashSet.add("me");
    hashSet.add("you ");
    hashSet.add("I");
    hashSet.add("Us");
    Iterator it = hashSet.iterator();
    long startTime = System.currentTimeMillis();
    while (it.hasNext()) {
        System.out.println(it.next());
    }
    return startTime;
}

public static void main(String[] args) {
    FindTime ft = new FindTime();
    long startTime = ft.m1();
    System.out.println("startTime" + startTime);
    long endTime = System.currentTimeMillis();
    System.out.println("End time" + endTime);
    System.out.println("d/W" + (endTime - startTime));
 }
}

I don't know is that one is correct way or not.My requirement is "I want to calculate time taken to Iterate a HashSet".

Upvotes: 3

Views: 10170

Answers (3)

Pankaj Goyal
Pankaj Goyal

Reputation: 980

As you telling you need time to take only for iterate not for insertion then you can use it like 

long m1() {
hashSet.add("hai");
hashSet.add("me");
hashSet.add("you ");
hashSet.add("I");
hashSet.add("Us");
Iterator it = hashSet.iterator();
long startTime = System.nanoTime();

while (it.hasNext()) {
    System.out.println(it.next());
}
long endTime = System.nanoTime();
System.out.println("time taken in nano seconds" + endTime-startTime); 
return endTime-startTime;
}

reason is if you take time into your main function then it will also calculate the time for insertion. Yes I am agree that it will not affect too much but we know that is not right thing to do.Even here I am printing so here also it will add the printing time that is not exactly correct.

Upvotes: 1

Deepak Bhatia
Deepak Bhatia

Reputation: 6276

To be more precise use System.nanoTime()

public class FindTime {

HashSet<String> hashSet = new HashSet<>();

long m1() 
{
    hashSet.add("hai");
    hashSet.add("me");
    hashSet.add("you ");
    hashSet.add("I");
    hashSet.add("Us");
    Iterator it = hashSet.iterator();
    long startTime = System.nanoTime();
    while (it.hasNext()) {
        System.out.println(it.next());
    }
    return startTime;
}

public static void main(String[] args) {
    FindTime ft = new FindTime();
    long startTime = ft.m1();

    long endTime = System.nanoTime(); //CALCULATE THE END TIME BEFORE PRINTING START TIME
           //BECAUSE PRINT OPERATION WILL ALSO TAKE TIME THAT WILL BE ADDED TO DIFFERENCE

    System.out.println("Start time in nano seconds" + startTime); //No need because you actually need difference

    System.out.println("End time in nano seconds" + endTime);
    System.out.println("Difference in Nano Seconds" + (endTime - startTime));
    //long microsecondsTime = (end - start) / 1000; //If you need in microseconds 
 }
}

Upvotes: 4

vels4j
vels4j

Reputation: 11298

Your code is correct. You've calculated the time which taken for iterating and printing the output in console. Print may take more time than iteration.

You may have also returned the execution time by return System.currentTimeMillis()- startTime;

See Also : Do not use System.out.println in server side code

Upvotes: 3

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