org.grouplens.lenskit.data

Class AbstractUserHistory<E extends Event>

java.lang.Object

java.util.AbstractCollection<E>

java.util.AbstractList<E>

org.grouplens.lenskit.data.AbstractUserHistory<E>

Type Parameters:

E - The type of event this history contains.

All Implemented Interfaces:

Iterable<E>, Collection<E>, List<E>, UserHistory<E>

Direct Known Subclasses:

BasicUserHistory

public abstract class AbstractUserHistory<E extends Event>
extends AbstractList<E>
implements UserHistory<E>

An abstract implementation of UserHistory to provide default implementations of convenience methods.

Author:

GroupLens Research

Compatibility: Public (may require additional method implementations across minor revisions)

Field Summary

Fields inherited from class java.util.AbstractList

modCount

Constructor Summary

Constructors

Constructor and Description
AbstractUserHistory()

Method Summary

Methods

Modifier and Type	Method and Description
LongSet	itemSet() Get the set of items touched by events in this history.
<T> T	memoize(Function<? super UserHistory<E>,? extends T> func) Apply a function to this history, memoizing its return value.

Methods inherited from class java.util.AbstractList

add, add, addAll, clear, equals, get, hashCode, indexOf, iterator, lastIndexOf, listIterator, listIterator, remove, removeRange, set, subList

Methods inherited from class java.util.AbstractCollection

addAll, contains, containsAll, isEmpty, remove, removeAll, retainAll, size, toArray, toArray, toString

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface org.grouplens.lenskit.data.UserHistory

filter, filter, getUserId

Methods inherited from interface java.util.List

add, add, addAll, addAll, clear, contains, containsAll, equals, get, hashCode, indexOf, isEmpty, iterator, lastIndexOf, listIterator, listIterator, remove, remove, removeAll, retainAll, set, size, subList, toArray, toArray

Constructor Detail

AbstractUserHistory

public AbstractUserHistory()

Method Detail

itemSet

public LongSet itemSet()

Description copied from interface: UserHistory

Get the set of items touched by events in this history. Only nonnegative item IDs are considered.

Specified by:

itemSet in interface UserHistory<E extends Event>

Returns:

The set of all item IDs used in events in this history.

memoize

public <T> T memoize(Function<? super UserHistory<E>,? extends T> func)

Description copied from interface: UserHistory

Apply a function to this history, memoizing its return value. Used for caching things like summaries. The function should appropriately define its Function.equals(Object) and Object.hashCode() methods in order for memoization to work well.

This method is not guaranteed to be synchronized. It is safe to memoize distinct functions in parallel, but potentially-parallel use of the same function must be synchronized by client code or the function may be called twice. The implementation in AbstractUserHistory uses a ConcurrentHashMap. Multiple calls are therefore safe, but may result in extra work. All implementations must maintain this safety guarantee, although they may do so by synchronizing this method.

Specified by:

memoize in interface UserHistory<E extends Event>

Type Parameters:

T - The return type of the function.

Parameters:

func - The function to call and memoize.

Returns:

The return value of func.