package org.neo4j.helpers.collection;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
import org.neo4j.helpers.Predicate;
/**
* An iterable which filters another iterable, only letting items with certain
* criterias pass through. All iteration/filtering is done lazily.
*
* @param <T> the type of items in the iteration.
*/
public class FilteringIterable<T> implements Iterable<T>
{
private final Iterable<T> source;
private final Predicate<T> predicate;
public FilteringIterable( Iterable<T> source, Predicate<T> predicate )
{
this.source = source;
this.predicate = predicate;
}
public Iterator<T> iterator()
{
return new FilteringIterator<T>( source.iterator(), predicate );
}
public static <T> Iterable<T> notNull( Iterable<T> source )
{
return new FilteringIterable<T>( source, FilteringIterable.<T>notNullPredicate() );
}
public static <T> Iterable<T> noDuplicates( Iterable<T> source )
{
return new FilteringIterable<T>( source, FilteringIterable.<T>noDuplicatesPredicate() );
}
public static <T> Predicate<T> noDuplicatesPredicate()
{
return new Predicate<T>()
{
private final Set<T> visitedItems = new HashSet<T>();
public boolean accept( T item )
{
return visitedItems.add( item );
}
};
}
@SuppressWarnings("unchecked")
public static <T> Predicate<T> notNullPredicate()
{
return (Predicate<T>) NOT_NULL_PREDICATE;
}
@SuppressWarnings("unchecked")
private static final Predicate NOT_NULL_PREDICATE = new Predicate()
{
public boolean accept( Object item )
{
return item != null;
}
};
}