Iterators Dan Fleck

Iterators Iterator JCF defines generic interface java.util.Iterator Object that can access a collection of objects one object at a time Traverses the collection of objects JCF defines generic interface java.util.Iterator And a subinterface ListIterator

Iterator Example ArrayList aList = new ArrayList(); populateListWithStrings(aList); Iterator itr = aList.iterator(); while (itr.hasNext()) { String nextStr = (String)itr.next(); System.out.printf(“List item is: %s”, nextStr); }

Iterator Example with Generics ArrayList<String> aList = new ArrayList<String>(); populateListWithStrings(aList); Iterator<String> itr = aList.iterator(); while (itr.hasNext()) { String nextStr = itr.next(); System.out.printf(“List item is: %s”, nextStr); }

Iterator methods See Javadoc for Iterator Do all Iterators implement the remove operation? What happens if they don’t? What is another way to iterate through a Collection (ArrayList, Vector, Set, HashSet, LinkedList, etc…)? Answer: New for loop!

ListIterator Extends iterator to allow reverse iteration of a List “hasPrevious()”, “previous” methods Has an add() method Has a set() method to replace elements Lets you get the index of the element Int nextIndex(), int previousIndex()