org.apache.jena.util.iterator

Class LazyIterator<T>

java.lang.Object

org.apache.jena.util.iterator.NiceIterator<T>

org.apache.jena.util.iterator.LazyIterator<T>

All Implemented Interfaces:

Iterator<T>, ClosableIterator<T>, ExtendedIterator<T>

public abstract class LazyIterator<T>
extends NiceIterator<T>

An ExtendedIterator that is created lazily. This is useful when constructing an iterator is expensive and you'd prefer to delay doing it until certain it's actually needed. For example, if you have iterator1.andThen(iterator2) you could implement iterator2 as a LazyIterator. The sequence to be defined is defined by the subclass's definition of create(). That is called exactly once on the first attempt to iterate (i.e. use one of the hasNext, next, remove, removeNext operations, maybe indirectly via toList).

Constructor Summary

Constructors

Constructor and Description
LazyIterator() An ExtendedIterator that is created lazily.

Method Summary

Modifier and Type	Method and Description
void	close() default close: don't need to do anything.
abstract ExtendedIterator<T>	create() The subclass must define this to return the ExtendedIterator to invoke.
boolean	hasNext() default hasNext: no elements, return false.
T	next() default next: throw an exception.
void	remove() default remove: we have no elements, so we can't remove any.

Methods inherited from class org.apache.jena.util.iterator.NiceIterator

andThen, andThen, asList, asSet, close, emptyIterator, filterDrop, filterKeep, mapWith, removeNext, toList, toSet

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface org.apache.jena.util.iterator.ExtendedIterator

nextOptional

Methods inherited from interface java.util.Iterator

forEachRemaining

Constructor Detail

LazyIterator

public LazyIterator()

An ExtendedIterator that is created lazily. This constructor has very low overhead - the real work is delayed until the first attempt to use the iterator.

Method Detail

hasNext

public boolean hasNext()

Description copied from class: NiceIterator

default hasNext: no elements, return false.

Specified by:

hasNext in interface Iterator<T>

Overrides:

hasNext in class NiceIterator<T>

next

public T next()

Description copied from class: NiceIterator

default next: throw an exception.

Specified by:

next in interface Iterator<T>

Overrides:

next in class NiceIterator<T>

remove

public void remove()

Description copied from class: NiceIterator

default remove: we have no elements, so we can't remove any.

Specified by:

remove in interface Iterator<T>

Overrides:

remove in class NiceIterator<T>

close

public void close()

Description copied from class: NiceIterator

default close: don't need to do anything.

Specified by:

close in interface ClosableIterator<T>

Overrides:

close in class NiceIterator<T>

create

public abstract ExtendedIterator<T> create()

The subclass must define this to return the ExtendedIterator to invoke. This method will be called at most once, on the first attempt to use the iterator. From then on, all calls to this will be passed through to the returned Iterator.

Returns:

The parent iterator defining the sequence.