HasNext iterator returns true, but the following exception throws

Question

I'm just curious how several iterators on the same object will behave and enter the following code.

import java.util.Map;
import java.util.HashMap;
import java.util.Iterator;

class Test{
  public static void main(String[] a) {
    Map<Integer,String> map = new HashMap<>();
    map.put(1,"One");

    Iterator<Integer> it1 = map.keySet().iterator();
    Iterator<Integer> it2 = map.keySet().iterator();

    it1.next();
    it1.remove();
    System.out.println(it2.hasNext());
    System.out.println(it2.next());

    System.out.println(map.get(1));
  }
}

The card is empty as expected. But I thought I would Iterator#hasNextreturn false, but instead I returned trueand Iterator#nextthrew a ConcurrentModificationException.

when a value is removed from Collectionusing the method Iterator#remove, should the other iterator method not hasNextreturn false since there would be no value to be returned?

Answer 1

The method hasNextchecks the attribute next:

public final boolean hasNext() {
  return next != null;
}

, next:

• nextEntry
• remove

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Answer 2

javadoc iterator.remove() :

, , - , .

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