org.janusgraph.graphdb.query

Class LimitAdjustingIterator<R>

java.lang.Object

org.janusgraph.graphdb.query.LimitAdjustingIterator<R>

All Implemented Interfaces:

Closeable, AutoCloseable, Iterator<R>, org.apache.tinkerpop.gremlin.structure.util.CloseableIterator<R>

public abstract class LimitAdjustingIterator<R>
extends Object
implements org.apache.tinkerpop.gremlin.structure.util.CloseableIterator<R>

An iterator implementation that wraps around another iterator to iterate it up to a given limit. The idea is that the wrapped iterator is based on data that is fairly expensive to retrieve (e.g. from a database). As such, we don't want to retrieve all of it but "just enough". However, if more data is requested, then we want the wrapped iterator to be updated (i.e. additional data be retrieved).

The limit for the wrapped iterator is updated by a factor of 2. When the iterator is updated, the iterator must be iterated through to the point of the last returned element. While this may seem expensive, it is less expensive than retrieving more than needed elements in the first place. However, this still means the initial currentLimit in the constructor should be chosen wisely.

Author:

Matthias Broecheler ([email protected])

Constructor Summary

Constructors

Constructor and Description
LimitAdjustingIterator(int maxLimit, int currentLimit) Initializes this iterator with the current limit and the maximum number of elements that may be retrieved from the wrapped iterator.

Method Summary

Modifier and Type	Method and Description
void	close()
abstract Iterator<R>	getNewIterator(int newLimit) This returns the wrapped iterator with up to the specified number of elements.
boolean	hasNext()
R	next()
void	remove()

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.apache.tinkerpop.gremlin.structure.util.CloseableIterator

asCloseable, closeIterator

Methods inherited from interface java.util.Iterator

forEachRemaining

Constructor Detail

LimitAdjustingIterator

public LimitAdjustingIterator(int maxLimit,
                              int currentLimit)

Initializes this iterator with the current limit and the maximum number of elements that may be retrieved from the wrapped iterator.

Parameters:

maxLimit -

currentLimit -

Method Detail

getNewIterator

public abstract Iterator<R> getNewIterator(int newLimit)

This returns the wrapped iterator with up to the specified number of elements.

Parameters:

newLimit -

Returns:

hasNext

public boolean hasNext()

Specified by:

hasNext in interface Iterator<R>

next

public R next()

Specified by:

next in interface Iterator<R>

remove

public void remove()

Specified by:

remove in interface Iterator<R>

close

public void close()

Specified by:

close in interface Closeable

Specified by:

close in interface AutoCloseable

Specified by:

close in interface org.apache.tinkerpop.gremlin.structure.util.CloseableIterator<R>