Using Iterator - java.util.ConcurrentModificationException

Question

So, this returns me

java.util.ConcurrentModificationException

and points to System.out.println line

Iterator<Autor> it = autores.iterator(); 
// Declaring a class iterator

public void listarAutores() {

    while (it.hasNext()) {
        String aux = it.next().getNomeCompleto(); 
        // Get string from Class Autor method
        System.out.println(aux);
        // Printing that string
    }
}

Why it's happening and how can i fix it?

You probably use the underlying Iterable in the while statement. — davidxxx
– davidxxx, Commented Dec 12, 2018 at 15:46

assylias · Accepted Answer · 2018-12-12 15:41:46Z

2

This can happen if you modify the collection between two calls to the method. For example:

listarAutores();
autores.add(anotherAuthor);
listarAutores();

You should create a new iterator in the method at every call or, even better, not use an iterator at all:

public void listarAutores() {
    for (Author a : autores) {
        String aux = a.getNomeCompleto(); 
        // Get string from Class Autor method
        System.out.println(aux);
        // Printing that string
    }
}

answered Dec 12, 2018 at 15:41

assylias

330k84 gold badges680 silver badges806 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Ousmane D. Over a year ago

or autores.forEach(a -> System.out.println(a.getNomeCompleto()));

Andy Thomas Over a year ago

The second form may also use an iterator - just an implicit one.

assylias Over a year ago

@AndyThomas Yes sure, I meant not explicitly use an iterator.

Murat Karagöz · Accepted Answer · 2018-12-12 15:41:31Z

1

Move your Iterator into the method call. You probably modify the Set somewhere in between.

answered Dec 12, 2018 at 15:41

Murat Karagöz

37.8k16 gold badges82 silver badges114 bronze badges

Collectives™ on Stack Overflow

Using Iterator - java.util.ConcurrentModificationException

2 Answers 2

3 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related