package org.neo4j.commons.iterator;
import java.util.Iterator;
/**
* For each item in the supplied iterator (called "surface item") there's
* instantiated an iterator from that item which is iterated before moving
* on to the next surface item.
*
* @param <T> the type of items to return
* @param <U> the type of items in the surface item iterator
*/
public abstract class NestingIterator<T, U> extends PrefetchingIterator<T>
{
private Iterator<U> source;
private Iterator<T> currentNestedIterator;
private U currentSurfaceItem;
public NestingIterator( Iterator<U> source )
{
this.source = source;
}
protected abstract Iterator<T> createNestedIterator( U item );
public U getCurrentSurfaceItem()
{
if ( this.currentSurfaceItem == null )
{
throw new IllegalStateException( "Has no surface item right now," +
" you must do at least one next() first" );
}
return this.currentSurfaceItem;
}
@Override
protected T fetchNextOrNull()
{
if ( currentNestedIterator == null ||
!currentNestedIterator.hasNext() )
{
while ( source.hasNext() )
{
currentSurfaceItem = source.next();
currentNestedIterator =
createNestedIterator( currentSurfaceItem );
if ( currentNestedIterator.hasNext() )
{
break;
}
}
}
return currentNestedIterator != null &&
currentNestedIterator.hasNext() ?
currentNestedIterator.next() : null;
}
}