Java Reference
In-Depth Information
Iterators
An iterator is something that allows you to examine and possibly modify the elements in a
collection in some sequential order. Java formalizes this concept with the two interfaces
Iterator<T>
and
ListIterator<T>
.
TIP: For-Each Loops as Iterators
A for-each loop is not strictly speaking an iterator (because, among other things, it is
not an object), but a for-each loop serves the same purpose as an iterator: it lets you
cycle through the elements in a collection. When dealing with collections, you can
often use a for-each loop in place of an iterator, and the for-each loop is usually sim-
pler and easier to use than an iterator. For example, in Display 16.14 we have rewritten
the program in Display 16.13 using for-each loops in place of iterators. Note that we
needed to do some extra programming with the variable
last
in order to simulate
i.remove( )
. Sometimes an iterator works best, and sometimes a for-each loop works
best. Many authorities would say that our code would be better if we had not replaced
the first iterator loop in Display 16.13 with a for-each loop.
■
Display 16.14
For-Each Loops as Iterators
(part 1 of 2)
1
import
java.util.HashSet;
2
import
java.util.Iterator;
3
public
class
ForEachDemo
4{
5
public
static
void
main(String[] args)
6
{
7
HashSet<String> s =
new
HashSet<String>( );
8
s.add("health");
9
s.add("love");
10
s.add("money");
11
System.out.println("The set contains:");
12
String last =
null
;
13
for
(String e : s)
14
{
15
last = e;
16
System.out.println(e);
17
}
