Question

I am having trouble using Iterator in java.

it=myHash.iterator();
 while (it.hasNext()) 
        if (it.next() satisfying something) 
            do something

 while (it.hasNext()) 
        if (it.next() satisfying something) 
            it.remove();

I am trying to iterate hashset twice, and the first loop making it.hasNext() return false. How to i resolve this?

I tried even adding the edit as you guys suggested, still not working…

Answer 1

You’re reusing the same iterator – and that’s been invalidated by adding new items to the set.

You should call iterator() again on the set:

it = set.iterator();

You can’t reset the existing iterator

EDIT: Here’s some sample code which shows this working:

import java.util.*;

public class Test {
    public static void main(String[] args) {
        Set<String> set = new HashSet<String>();

        set.add("food");
        set.add("bad");
        set.add("hungry");
        set.add("neighbour");

        Iterator<String> it = set.iterator();

        // Remove any string longer than 4
        while (it.hasNext())
        {
            if (it.next().length() > 4)
            {
                it.remove();
            }
        }

        set.add("new long text");
        set.add("x");

        // Remove any string shorter than 4
        it = set.iterator();

        while (it.hasNext())
        {
            if (it.next().length() < 4)
            {
                it.remove();
            }
        }

        // Dump the results
        for (String x : set)
        {
            System.out.println(x);
        }
    }
}

This gives the results “new long text” and “food”.