CODEWITHSUNDEEP
javaiterator
NumberTen
NumberTen

Reputation: 94

Issue with Iterator reuse

In this first while I used my Iterator and everything went well ;

ListIterator<Client> it = people.listIterator();      
while(it.hasNext()){
  Client c = (Client)it.next();
  System.out.println(c.getValeur());
}
System.out.println("Doing some operations on my values");

But when i did those operations on my values 

for (Client client : people) {
  int i = client.getValeur();
  i += 10000;
  client.setValeur(i);
}

And used the same iterator, I didn't Work 

while(it.hasNext()){
  Client c = (Client) it.next();
  System.out.println(c.getValeur());
}

Do I have to re-initiate the index of my iterator ?

Upvotes: 1

Views: 1495

Answers (5)

Makoto
Makoto

Reputation: 106389

An iterator is one-and-done; once it reaches the end of its iteration, it's not going to pick back up from the beginning.

Instead, from the structure of your problem space alone, there shouldn't be any reason that you can't perform all operations at once within the same iterator.

int i = 0;
ListIterator<Client> it = people.listIterator();      
while(it.hasNext()){
    Client c = it.next();
    System.out.println(c.getValeur());
    i = client.getValeur();
    i += 10000;
    client.setValeur(i);
}
System.out.println("Doing some operations on my values");

Upvotes: 0

Mik378
Mik378

Reputation: 22171

That's why it's not recommanded at all to use a while loop dealing with an Iterator.

Why? Because the scope is not delimited when using while and may cause some trouble like you encountered.

Prefer using this pattern:

for(Iterator it = people.listIterator(); it.hasNext();){
   Client c = (Client)it.next();
   System.out.println(c.getValeur());
}
//can't access it right here (outside the loop) any more

This way, you can't reach again the iterator (that itself finishes it's job and cannot be reset) since it's now out of the scope.

To sum up, this pattern forces you to instantiates a new Iterator to loop again over the collection and this is the way to do.

Upvotes: 1

Andreas Dolk
Andreas Dolk

Reputation: 114757

Yes, get a new one. An Iterator can't be reset or rewinded. It iterates in one direction and should be thrown away after.

Upvotes: 3

Adam Siemion
Adam Siemion

Reputation: 16029

Your iterator has reached the end and you have to instantiate a new one so that it points to the first element of the list.

Upvotes: 1

Andrew Thompson
Andrew Thompson

Reputation: 168815

Do I have to re-initiate the index of my iterator ?

No, they cannot be 'wound back'. Get a new iterator.

Upvotes: 1

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