Iterators
Dan Fleck
Iterators

Iterator

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
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
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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…)?
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
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Int nextIndex(), int previousIndex()