org.lenskit.util.io

Class GroupingObjectStream<C,E>

java.lang.Object

org.lenskit.util.io.AbstractObjectStream<C>

org.lenskit.util.io.GroupingObjectStream<C,E>

All Implemented Interfaces:

Closeable, AutoCloseable, Iterable<C>, ObjectStream<C>

public abstract class GroupingObjectStream<C,E>
extends AbstractObjectStream<C>

Base class for streams that group the output of another stream.

Since:

2.1

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	GroupingObjectStream(ObjectStream<? extends E> base)

Method Summary

Modifier and Type	Method and Description
protected abstract void	clearGroup() Clear the accumulated group.
void	close() No-op implementation of the ObjectStream.close() method.
protected abstract C	finishGroup() Finish the current group and return it.
protected abstract boolean	handleItem(E item) Handle an item from the base stream.
C	readObject() Read the next object from this stream.

Methods inherited from class org.lenskit.util.io.AbstractObjectStream

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

GroupingObjectStream

protected GroupingObjectStream(@WillCloseWhenClosed
                               ObjectStream<? extends E> base)

Method Detail

readObject

@Nullable
public C readObject()

Description copied from interface: ObjectStream

Read the next object from this stream.

Returns:

The next object, or null if at the end of the stream.

close

public void close()

Description copied from class: AbstractObjectStream

No-op implementation of the ObjectStream.close() method.

Specified by:

close in interface Closeable

Specified by:

close in interface AutoCloseable

Specified by:

close in interface ObjectStream<C>

Overrides:

close in class AbstractObjectStream<C>

clearGroup

protected abstract void clearGroup()

Clear the accumulated group. Called by close().

handleItem

protected abstract boolean handleItem(@Nonnull
                                      E item)

Handle an item from the base stream. Each item of the base stream is passed to this method. The method builds up the underlying aggregate.

Parameters:

item - The item to handle.

Returns:

true if the item has been accepted and added to the group; false if it cannot be added to the current group. If it cannot be added to the current group, the stream will call finishGroup() to finish the group, and then call this method again with item (at which point it is required to return true).

finishGroup

@Nonnull
protected abstract C finishGroup()

Finish the current group and return it. After this method has been called, #handleItem(E) should add items to a new group. This method will not be called unless #handleItem(E) has been called at least once since the last group was finished.

Returns:

The group that has been finished.