org.grouplens.lenskit.cursors

Class AbstractPollingCursor<T>

java.lang.Object

org.grouplens.lenskit.cursors.AbstractCursor<T>

org.grouplens.lenskit.cursors.AbstractPollingCursor<T>

Type Parameters:

T -

All Implemented Interfaces:

Closeable, AutoCloseable, Iterable<T>, Cursor<T>

Direct Known Subclasses:

DelimitedTextRatingCursor, LineCursor

public abstract class AbstractPollingCursor<T>
extends AbstractCursor<T>

An extension of AbstractCursor that simplifies the mechanics of the next()/hasNext() implementation to a simple method, poll().

Compatibility

Public

Constructor Summary

Constructors

Constructor and Description
AbstractPollingCursor() Construct a cursor of unknown size.
AbstractPollingCursor(int rowCount) Construct a cursor with a known number of rows.

Method Summary

Modifier and Type	Method and Description
protected T	copy(T obj) Construct a copy of an object.
T	fastNext() Deprecated.
boolean	hasNext() Query whether the cursor has any more items.
T	next() Fetch the next item from the cursor.
protected abstract T	poll() Return the next element in this Cursor, or null if there are no more elements.

Methods inherited from class org.grouplens.lenskit.cursors.AbstractCursor

close, fast, getRowCount, iterator

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.lang.Iterable

forEach, spliterator

Constructor Detail

AbstractPollingCursor

public AbstractPollingCursor()

Construct a cursor of unknown size.

AbstractPollingCursor

public AbstractPollingCursor(int rowCount)

Construct a cursor with a known number of rows.

Parameters:

rowCount - The number of rows, or -1 for unknown size.

Method Detail

hasNext

public boolean hasNext()

Description copied from interface: Cursor

Query whether the cursor has any more items. If the cursor or underlying source has been closed, this may return even if the end has not been reached.

Returns:

true if there remains another item to fetch.

fastNext

@Nonnull
 @Deprecated
public T fastNext()

Deprecated.

Description copied from class: AbstractCursor

Variant of Cursor.next() that may mutate and return the same object avoid excess allocations. Since many loops don't do anything with the object after the iteration in which it is retrieved, using this iteration method can improve both speed and memory use.

This implementation delegates to Cursor.next().

Specified by:

fastNext in interface Cursor<T>

Overrides:

fastNext in class AbstractCursor<T>

Returns:

The next element from the cursor, reusing objects if possible.

See Also:

Cursor.next()

next

@Nonnull
public T next()

Description copied from interface: Cursor

Fetch the next item from the cursor.

Returns:

The next item in the cursor.

poll

protected abstract T poll()

Return the next element in this Cursor, or null if there are no more elements. This must be safe to call multiple times at the end of its collection. The same element object is allowed to be reused (fast iteration), so long as copy(Object) copies objects. If this method returns a fresh object every time, then copy(Object) should be a no-op.

Returns:

The next element, or null

copy

protected T copy(T obj)

Construct a copy of an object. The default does not copy; it just returns its parameter. If a subclass wants to fast iteration to actually be fast (mutate and reuse the same object), it should do so in its poll() method, and override this method to create a new copy of an object for when next() is called. Subclasses which return fresh objects on each call to poll() do not need to override this method.

Parameters:

obj - The object to copy.

Returns:

A copy of obj.