Java - adding elements to list while iterating over it

Question

I want to avoid getting ConcurrentModificationException. How would I do it?

Answer 1

You may use a ListIterator which has support for a remove/add method during the iteration itself.

ListIterator<Book> iter = books.listIterator(); while(iter.hasNext()){     if(iter.next().getIsbn().equals(isbn)){         iter.add(new Book(...));     } } 

Answer 2

Instead of using an iterator, you can use a for loop with an index. For example:

int originalLength = list.length(); for (int i = 0; i < originalLength; i++) {   MyType mt = list.get(i);   //... processing   //... insertions } 

Answer 3

You want to use a ListIterator. You can get one of these from any kind of list, though for efficiency you probably want to get one from a LinkedList.

import java.util.*;
class TestListIterator {
  public static void main(String[]args) {
    List<Integer> L = new LinkedList<Integer>();
    L.add(0);
    L.add(1);
    L.add(2);
    for (ListIterator<Integer> i = L.listIterator(); i.hasNext(); ) {
      int x = i.next();
      i.add(x + 10);
    }
    System.out.println(L);
  }
}

Prints [0, 10, 1, 11, 2, 12].