element at a time. In general, to use an iterator to cycle through the contents of a collection,
follow these steps:
1. Obtain an iterator to the start of the collection by calling the collection's iterator( )
method.
2. Set up a loop that makes a call to hasNext( ). Have the loop iterate as long as hasNext( )
returns true.
3. Within the loop, obtain each element by calling next( ).
For collections that implement List, you can also obtain an iterator by calling listIterator( ).
As explained, a list iterator gives you the ability to access the collection in either the forward
or backward direction and lets you modify an element. Otherwise, ListIterator is used just
like Iterator.
The following example implements these steps, demonstrating both the Iterator and
ListIterator interfaces. It uses an ArrayList object, but the general principles apply to any
type of collection. Of course, ListIterator is available only to those collections that implement
the List interface.
// Demonstrate iterators.
import java.util.*;
class IteratorDemo {
public static void main(String args[]) {
// Create an array list.
ArrayList<String> al = new ArrayList<String>();
// Add elements to the array list.
al.add("C");
al.add("A");
al.add("E");
al.add("B");
al.add("D");
al.add("F");
// Use iterator to display contents of al.
System.out.print("Original contents of al: ");
Iterator<String> itr = al.iterator();
while(itr.hasNext()) {
String element = itr.next();
System.out.print(element + " ");
}
System.out.println();
// Modify objects being iterated.
ListIterator<String> litr = al.listIterator();
while(litr.hasNext()) {
String element = litr.next();
litr.set(element + "+");
}
System.out.print("Modified contents of al: ");
itr = al.iterator();
while(itr.hasNext()) {
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