com.hp.hpl.jena.util.iterator
Class LazyIterator

java.lang.Object
  com.hp.hpl.jena.util.iterator.LazyIterator

All Implemented Interfaces:

ClosableIterator, ExtendedIterator, java.util.Iterator

public abstract class LazyIterator

extends java.lang.Object

implements ExtendedIterator

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 interact with the LazyIterator.

Version:

$Revision: 1.1 $

Author:

jjc, modified to use ExtendedIterators by csayers

Constructor Summary

LazyIterator()
An ExtendedIterator that is created lazily.

Method Summary

ExtendedIterator	andThen(ClosableIterator other) return a new iterator which delivers all the elements of this iterator and then all the elements of the other iterator.
void	close() Close the iterator
abstract ExtendedIterator	create() The subclass must define this to return the ExtendedIterator to invoke.
ExtendedIterator	filterDrop(Filter f) return a new iterator containing only the elements of _this_ which are rejected by the filter _f_.
ExtendedIterator	filterKeep(Filter f) return a new iterator containing only the elements of _this_ which pass the filter _f_.
boolean	hasNext()
ExtendedIterator	mapWith(Map1 map1) return a new iterator where each element is the result of applying _map1_ to the corresponding element of _this_.
java.lang.Object	next()
void	remove()

Methods inherited from class java.lang.Object

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

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()

Specified by:

hasNext in interface java.util.Iterator

next

public java.lang.Object next()

Specified by:

next in interface java.util.Iterator

remove

public void remove()

Specified by:

remove in interface java.util.Iterator

andThen

public ExtendedIterator andThen(ClosableIterator other)

Description copied from interface: ExtendedIterator

return a new iterator which delivers all the elements of this iterator and then all the elements of the other iterator. Does not copy either iterator; they are consumed as the result iterator is consumed.

Specified by:

andThen in interface ExtendedIterator

filterKeep

public ExtendedIterator filterKeep(Filter f)

Description copied from interface: ExtendedIterator

return a new iterator containing only the elements of _this_ which pass the filter _f_. The order of the elements is preserved. Does not copy _this_, which is consumed as the result is consumed.

Specified by:

filterKeep in interface ExtendedIterator

filterDrop

public ExtendedIterator filterDrop(Filter f)

Description copied from interface: ExtendedIterator

return a new iterator containing only the elements of _this_ which are rejected by the filter _f_. The order of the elements is preserved. Does not copy _this_, which is consumed as the reult is consumed.

Specified by:

filterDrop in interface ExtendedIterator

mapWith

public ExtendedIterator mapWith(Map1 map1)

Description copied from interface: ExtendedIterator

return a new iterator where each element is the result of applying _map1_ to the corresponding element of _this_. _this_ is not copied; it is consumed as the result is consumed.

Specified by:

mapWith in interface ExtendedIterator

close

public void close()

Description copied from interface: ClosableIterator

Close the iterator

Specified by:

close in interface ClosableIterator

create

public abstract ExtendedIterator 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.