Vector vs LinkedHashSet iteration speed

[Ruben Soto]

According to Devaka, Practice Exam 3, Question 60, LinkedHashSet has a faster iteration speed than Vector. I don't think you can compare these two for iteration speed however. While it is true that Vector has synchronized methods, which are a disadvantage in terms of performance, it can iterate by sequential indexing, whereas LinkedHashSet would need to iterate by following the links through reference access, which I think could be slower. Any ideas?

[Deepak Bala]

The Vector is probably at a disadvantage because its methods are synchronized. I gave this a try with a program and the iteration speed is marginally better for the linked hash set.

  
import java.util.Collection;
import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Set;
import java.util.Vector;


public class SpeedTest
{

    /**
     * @param args
     */
    public static void main(String[] args)
    {
        SpeedTest speedTest = new SpeedTest();
        speedTest.go();
    }
    
    private void go()
    {
        Set<Object> set = new LinkedHashSet<Object>(1000001);
        List<Object> list = new Vector<Object>(1000001);
        populate(set);
        populate(list);
        iterate(set.iterator());
        iterate(list.iterator());
        System.out.println(set.size() + " " + list.size());
    }
    
    private void populate(Collection<Object> collection)
    {
        long past= System.currentTimeMillis();
        for (int iCounter=0; iCounter<1000000; iCounter++)
        {
            collection.add(new Object());
        }
        System.out.println("Time taken to populate: " + (System.currentTimeMillis() - past));
    }
    
    private void iterate(Iterator<Object> iterator)
    {
        long past= System.currentTimeMillis();
        while (iterator.hasNext())
        {
            iterator.next();
        }
        System.out.println("Time taken to iterate: " + (System.currentTimeMillis() - past));
    }
}

  

Result

Time taken to populate: 2344
Time taken to populate: 203
Time taken to iterate: 78
Time taken to iterate: 141
1000000 1000000

[NagarajGoud uppala]

Hi deepak,
nice explanation!

[Mansi Mishra]

@Deepak
That was a good explanation...

[Chaitanya Jadhav]

Deepu,

nice example

[Ruben Soto]

Deepak Bala wrote:The Vector is probably at a disadvantage because its methods are synchronized. I gave this a try with a program and the iteration speed is marginally better for the linked hash set.

Thanks a lot, Deepak. Great example! I think using a practical example is the only way to see which one is faster, because there is no qualitative theoretical principle that dictates one will be faster than the other (whereas, for example, a LinkedHashSet will always have faster iteration than a HashSet, and a HashMap will have faster iteration than a Hashtable, for theoretical reasons.)

Again, great example!