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*
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*
* The iterator will loop continuously around the provided elements, unless
* there are no elements in the collection to begin with, or all the elements
* have been {@link #remove removed}.
*
* Concurrent modifications are not directly supported, and for most collection
* implementations will throw a ConcurrentModificationException.
*
* @since Commons Collections 3.0
* @version $Revision: 1.8 $ $Date: 2004/01/14 21:43:14 $
*
* @author Jonathan Carlson
* @author Stephen Colebourne
*/
public class LoopingIterator implements ResettableIterator {
/** The collection to base the iterator on */
private Collection collection;
/** The current iterator */
private Iterator iterator;
/**
* Constructor that wraps a collection.
*
* There is no way to reset an Iterator instance without recreating it from
* the original source, so the Collection must be passed in.
*
* @param coll the collection to wrap
* @throws NullPointerException if the collection is null
*/
public LoopingIterator(Collection coll) {
if (coll == null) {
throw new NullPointerException("The collection must not be null");
}
collection = coll;
reset();
}
/**
* Has the iterator any more elements.
*
* Returns false only if the collection originally had zero elements, or
* all the elements have been {@link #remove removed}.
*
* @return true if there are more elements
*/
public boolean hasNext() {
return (collection.size() > 0);
}
/**
* Returns the next object in the collection.
*
* If at the end of the collection, return the first element.
*
* @throws NoSuchElementException if there are no elements
* at all. Use {@link #hasNext} to avoid this error.
*/
public Object next() {
if (collection.size() == 0) {
throw new NoSuchElementException("There are no elements for this iterator to loop on");
}
if (iterator.hasNext() == false) {
reset();
}
return iterator.next();
}
/**
* Removes the previously retrieved item from the underlying collection.
*
* This feature is only supported if the underlying collection's
* {@link Collection#iterator iterator} method returns an implementation
* that supports it.
*
* This method can only be called after at least one {@link #next} method call.
* After a removal, the remove method may not be called again until another
* next has been performed. If the {@link #reset} is called, then remove may
* not be called until {@link #next} is called again.
*/
public void remove() {
iterator.remove();
}
/**
* Resets the iterator back to the start of the collection.
*/
public void reset() {
iterator = collection.iterator();
}
/**
* Gets the size of the collection underlying the iterator.
*
* @return the current collection size
*/
public int size() {
return collection.size();
}
}