com.apple.foundationdb.record.cursors

Class EmptyCursor<T>

java.lang.Object

com.apple.foundationdb.record.cursors.EmptyCursor<T>

Type Parameters:

T - the type of elements of the cursor

All Implemented Interfaces:

RecordCursor<T>, AutoCloseable, Iterator<T>

@API(value=MAINTAINED)
public class EmptyCursor<T>
extends Object
implements RecordCursor<T>

A RecordCursor that always returns zero items.

Nested Class Summary

Nested classes/interfaces inherited from interface com.apple.foundationdb.record.RecordCursor

RecordCursor.NoNextReason

Constructor Summary

Constructors

Constructor and Description
EmptyCursor(Executor executor)

Method Summary

Modifier and Type	Method and Description
boolean	accept(RecordCursorVisitor visitor) Accept a visit from hierarchical visitor, which implements RecordCursorVisitor.
void	close()
byte[]	getContinuation() Deprecated.
Executor	getExecutor()
RecordCursorResult<T>	getNext() Get the next result from this cursor.
RecordCursor.NoNextReason	getNoNextReason() Deprecated.
T	next() Deprecated.
CompletableFuture<Boolean>	onHasNext() Deprecated.
CompletableFuture<RecordCursorResult<T>>	onNext() Asynchronously return the next result from this cursor.

Methods inherited from class java.lang.Object

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

Methods inherited from interface com.apple.foundationdb.record.RecordCursor

asIterator, asList, empty, empty, filter, filterAsync, filterAsyncInstrumented, filterAsyncInstrumented, filterInstrumented, filterInstrumented, first, flatMapPipelined, flatMapPipelined, flatMapPipelined, forEach, forEachAsync, forEachResult, forEachResultAsync, fromFuture, fromFuture, fromIterator, fromIterator, fromList, fromList, fromList, fromList, getCount, hasNext, limitRowsTo, limitTo, map, mapEffect, mapEffect, mapFuture, mapPipelined, orElse, reduce, skip, skipThenLimit

Methods inherited from interface java.util.Iterator

forEachRemaining, remove

Constructor Detail

EmptyCursor

public EmptyCursor(@Nonnull
                   Executor executor)

Method Detail

onNext

@Nonnull
public CompletableFuture<RecordCursorResult<T>> onNext()

Description copied from interface: RecordCursor

Asynchronously return the next result from this cursor. When complete, the future will contain a RecordCursorResult, which represents exactly one of the following:

1. The next object of type T produced by the cursor. In addition to the next record, this result includes a RecordCursorContinuation that can be used to continue the cursor after the last record returned. The returned continuation is guaranteed not to be an "end continuation" representing the end of the cursor: specifically, RecordCursorContinuation.isEnd() is always false on the returned continuation.
2. The fact that the cursor is stopped and cannot produce another record and a RecordCursor.NoNextReason that explains why no record could be produced. The result include a continuation that can be used to continue the cursor after the last record returned. If the result's NoNextReason is anything other than RecordCursor.NoNextReason.SOURCE_EXHAUSTED, the returned continuation must not be an end continuation. Conversely, if the result's NoNextReason is SOURCE_EXHAUSTED, then the returned continuation must be an an "end continuation".

In either case, the returned RecordCursorContinuation can be serialized to an opaque byte array using RecordCursorContinuation.toBytes(). This can be passed back into a new cursor of the same type, with all other parameters remaining the same.

Specified by:

onNext in interface RecordCursor<T>

Returns:

a future for the next result from this cursor representing either the next record or an indication of why the cursor stopped

See Also:

RecordCursorResult, RecordCursorContinuation

getNext

@Nonnull
public RecordCursorResult<T> getNext()

Description copied from interface: RecordCursor

Get the next result from this cursor. In many cases, this is a blocking operation and should not be called within asynchronous contexts. The non-blocking version of this function, RecordCursor.onNext(), should be preferred in such circumstances.

Specified by:

getNext in interface RecordCursor<T>

Returns:

the next result from this cursor representing either the next record or an indication of why the cursor stopped

See Also:

RecordCursor.onNext(), RecordCursorResult, RecordCursorContinuation

onHasNext

@Nonnull
 @Deprecated
public CompletableFuture<Boolean> onHasNext()

Deprecated.

Description copied from interface: RecordCursor

Asynchronously check whether there are more records available from the cursor.

Specified by:

onHasNext in interface RecordCursor<T>

Returns:

a future that when complete will hold true if RecordCursor.next() would return a record.

See Also:

AsyncIterator.onHasNext()

next

@Nullable
 @Deprecated
public T next()

Deprecated.

Description copied from interface: RecordCursor

Return the next value.

Specified by:

next in interface RecordCursor<T>

Specified by:

next in interface Iterator<T>

Returns:

the next value

getContinuation

@Nullable
 @Deprecated
public byte[] getContinuation()

Deprecated.

Description copied from interface: RecordCursor

Get a byte string that can be used to continue a query after the last record returned.

Specified by:

getContinuation in interface RecordCursor<T>

Returns:

opaque byte array denoting where the cursor should pick up. This can be passed back into a new cursor of the same type, with all other parameters remaining the same. Returns null if the underlying source is completely exhausted, independent of any limit passed to the cursor creator. Since such creators generally accept null to mean no continuation, that is, start from the beginning, one must check for null from getContinuation to keep from starting over. Result is not always defined if called before onHasNext or before next after onHasNext has returned true. That is, a continuation is only guaranteed when called "between" records from a while (hasNext) next loop or after its end.

getNoNextReason

@Nonnull
 @Deprecated
public RecordCursor.NoNextReason getNoNextReason()

Deprecated.

Description copied from interface: RecordCursor

Get the reason that the cursor has reached the end and returned false for RecordCursor.hasNext(). If hasNext was not called or returned true last time, the result is undefined and may be an exception.

Specified by:

getNoNextReason in interface RecordCursor<T>

Returns:

the reason that the cursor stopped

close

public void close()

Specified by:

close in interface RecordCursor<T>

Specified by:

close in interface AutoCloseable

getExecutor

@Nonnull
public Executor getExecutor()

Specified by:

getExecutor in interface RecordCursor<T>

accept

public boolean accept(@Nonnull
                      RecordCursorVisitor visitor)

Description copied from interface: RecordCursor

Accept a visit from hierarchical visitor, which implements RecordCursorVisitor. By contract, implementations of this method must return the value of visitor.visitLeave(this), which determines whether or not subsequent siblings of this cursor should be visited.

Specified by:

accept in interface RecordCursor<T>

Parameters:

visitor - a hierarchical visitor

Returns:

true if the subsequent siblings of the cursor should be visited, and false otherwise