Jakarta Commons Cookbook

5.2. Using a Looping Iterator

Problem

You need to loop through the contents of a Collection.

Solution

Use a LoopingIterator to repeatedly iterate through the contents of a Collection. Pass an existing Collection to the constructor of LoopingIterator, and call iterator( ). The following code uses a LoopingIterator to retrieve five items from a List with three items:

List drivers = new ArrayList( );

drivers.add( "Chris" );
drivers.add( "Sean" );
drivers.add( "Kathy" );

LoopingIterator loopingIterator = new LoopingIterator( drivers );

for( int i = 1; i <= 5; i++ ) {
    String driver = (String) loopingIterator.next( );
    System.out.println( "Driver for Day " + i + ": " + driver );
}

The previous example simulates the selection of a driver in a car pool with three drivers. Five drivers are selected, and the LoopingIterator returns the first item in the List on the fourth day:

Driver for Day 1: Chris
Driver for Day 2: Sean
Driver for Day 3: Kathy
Driver for Day 4: Chris
Driver for Day 5: Sean

Discussion

Keep in mind that a LoopingIterator never stops iterating; hasNext( ) always returns true in a LoopingIterator. If you are using a LoopingIterator with a while loop, be sure to code an exit condition. A LoopingIterator is appropriate for a situation in which a series of values must be repeatedly evaluated, or a loop of commands must be repeatedly executed. An application, for example, may have a series of components that need to be continuously updated, or a series of queues or buffers that ...