Class EmptyIterator
- java.lang.Object
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- org.apache.accumulo.core.iteratorsImpl.system.EmptyIterator
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- All Implemented Interfaces:
SortedKeyValueIterator<Key,Value>
,YieldingKeyValueIterator<Key,Value>
,InterruptibleIterator
public class EmptyIterator extends Object implements InterruptibleIterator
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Field Summary
Fields Modifier and Type Field Description static EmptyIterator
EMPTY_ITERATOR
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Constructor Summary
Constructors Constructor Description EmptyIterator()
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description SortedKeyValueIterator<Key,Value>
deepCopy(IteratorEnvironment env)
Creates a deep copy of this iterator as though seek had not yet been called.Key
getTopKey()
Returns top key.Value
getTopValue()
Returns top value.boolean
hasTop()
Returns true if the iterator has more elements.void
init(SortedKeyValueIterator<Key,Value> source, Map<String,String> options, IteratorEnvironment env)
Initializes the iterator.void
next()
Advances to the next K,V pair.void
seek(Range range, Collection<ByteSequence> columnFamilies, boolean inclusive)
Seeks to the first key in the Range, restricting the resulting K,V pairs to those with the specified columns.void
setInterruptFlag(AtomicBoolean flag)
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Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
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Methods inherited from interface org.apache.accumulo.core.iterators.SortedKeyValueIterator
isRunningLowOnMemory
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Methods inherited from interface org.apache.accumulo.core.iterators.YieldingKeyValueIterator
enableYielding
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Field Detail
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EMPTY_ITERATOR
public static final EmptyIterator EMPTY_ITERATOR
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Method Detail
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init
public void init(SortedKeyValueIterator<Key,Value> source, Map<String,String> options, IteratorEnvironment env) throws IOException
Description copied from interface:SortedKeyValueIterator
Initializes the iterator. Data should not be read from the source in this method.- Specified by:
init
in interfaceSortedKeyValueIterator<Key,Value>
- Parameters:
source
-SortedKeyValueIterator
source to read data from.options
-Map
map of string option names to option values.env
-IteratorEnvironment
environment in which iterator is being run, provided by Accumulo itself and is expected to be non-null.- Throws:
IOException
- unused.
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hasTop
public boolean hasTop()
Description copied from interface:SortedKeyValueIterator
Returns true if the iterator has more elements. Note that if this iterator has yielded (@see YieldingKeyValueIterator.enableYielding(YieldCallback)), this this method must return false.- Specified by:
hasTop
in interfaceSortedKeyValueIterator<Key,Value>
- Returns:
true
if the iterator has more elements.
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next
public void next() throws IOException
Description copied from interface:SortedKeyValueIterator
Advances to the next K,V pair. Note that in minor compaction scope and in non-full major compaction scopes the iterator may see deletion entries. These entries should be preserved by all iterators except ones that are strictly scan-time iterators that will never be configured for the minc or majc scopes. Deletion entries are only removed during full major compactions.- Specified by:
next
in interfaceSortedKeyValueIterator<Key,Value>
- Throws:
IOException
- if an I/O error occurs.
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seek
public void seek(Range range, Collection<ByteSequence> columnFamilies, boolean inclusive) throws IOException
Description copied from interface:SortedKeyValueIterator
Seeks to the first key in the Range, restricting the resulting K,V pairs to those with the specified columns. An iterator does not have to stop at the end of the range. The whole range is provided so that iterators can make optimizations. Seek may be called multiple times with different parameters afterSortedKeyValueIterator.init(org.apache.accumulo.core.iterators.SortedKeyValueIterator<K, V>, java.util.Map<java.lang.String, java.lang.String>, org.apache.accumulo.core.iterators.IteratorEnvironment)
is called. Iterators that examine groups of adjacent key/value pairs (e.g. rows) to determine their top key and value should be sure that they properly handle a seek to a key in the middle of such a group (e.g. the middle of a row). Even if the client always seeks to a range containing an entire group (a,c), the tablet server could send back a batch of entries corresponding to (a,b], then reseek the iterator to range (b,c) when the scan is continued.columnFamilies
is used, at the lowest level, to determine which data blocks inside of an RFile need to be opened for this iterator. This set of data blocks is also the set of locality groups defined for the given table. If no columnFamilies are provided, the data blocks for all locality groups inside of the correct RFile will be opened and seeked in an attempt to find the correct start key, regardless of the startKey in therange
. In an Accumulo instance in which multiple locality groups exist for a table, it is important to ensure thatcolumnFamilies
is properly set to the minimum required column families to ensure that data from separate locality groups is not inadvertently read.- Specified by:
seek
in interfaceSortedKeyValueIterator<Key,Value>
- Parameters:
range
-Range
of keys to iterate over.columnFamilies
-Collection
of column families to include or exclude.inclusive
-boolean
that indicates whether to include (true) or exclude (false) column families.- Throws:
IOException
- if an I/O error occurs.
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getTopKey
public Key getTopKey()
Description copied from interface:SortedKeyValueIterator
Returns top key. Can be called 0 or more times without affecting behavior of next() or hasTop(). Note that in minor compaction scope and in non-full major compaction scopes the iterator may see deletion entries. These entries should be preserved by all iterators except ones that are strictly scan-time iterators that will never be configured for the minc or majc scopes. Deletion entries are only removed during full major compactions.For performance reasons, iterators reserve the right to reuse objects returned by
getTopKey
whenSortedKeyValueIterator.next()
is called, changing the data that the object references. Iterators that need to save an object returned bygetTopKey
ought to copy the object's data into a new object in order to avoid aliasing bugs.- Specified by:
getTopKey
in interfaceSortedKeyValueIterator<Key,Value>
- Returns:
K
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getTopValue
public Value getTopValue()
Description copied from interface:SortedKeyValueIterator
Returns top value. Can be called 0 or more times without affecting behavior of next() or hasTop().For performance reasons, iterators reserve the right to reuse objects returned by
getTopValue
whenSortedKeyValueIterator.next()
is called, changing the underlying data that the object references. Iterators that need to save an object returned bygetTopValue
ought to copy the object's data into a new object in order to avoid aliasing bugs.- Specified by:
getTopValue
in interfaceSortedKeyValueIterator<Key,Value>
- Returns:
V
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deepCopy
public SortedKeyValueIterator<Key,Value> deepCopy(IteratorEnvironment env)
Description copied from interface:SortedKeyValueIterator
Creates a deep copy of this iterator as though seek had not yet been called. init should be called on an iterator before deepCopy is called. init should not need to be called on the copy that is returned by deepCopy; that is, when necessary init should be called in the deepCopy method on the iterator it returns. The behavior is unspecified if init is called after deepCopy either on the original or the copy. A proper implementation would call deepCopy on the source.- Specified by:
deepCopy
in interfaceSortedKeyValueIterator<Key,Value>
- Parameters:
env
-IteratorEnvironment
environment in which iterator is being run, provided by Accumulo itself and is expected to be non-null.- Returns:
SortedKeyValueIterator
a copy of this iterator (with the same source and settings).
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setInterruptFlag
public void setInterruptFlag(AtomicBoolean flag)
- Specified by:
setInterruptFlag
in interfaceInterruptibleIterator
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