javax.microedition.rms
Interface RecordEnumeration


public interface RecordEnumeration

A class representing a bidirectional record store Record enumerator. The RecordEnumeration logically maintains a sequence of the recordId's of the records in a record store. The enumerator will iterate over all (or a subset, if an optional record filter has been supplied) of the records in an order determined by an optional record comparator.

By using an optional RecordFilter, a subset of the records can be chosen that match the supplied filter. This can be used for providing search capabilities.

By using an optional RecordComparator, the enumerator can index through the records in an order determined by the comparator. This can be used for providing sorting capabilities.

If, while indexing through the enumeration, some records are deleted from the record store, the recordId's returned by the enumeration may no longer represent valid records. To avoid this problem, the RecordEnumeration can optionally become a listener of the RecordStore and react to record additions and deletions by recreating its internal index. Use special care when using this option however, in that every record addition, change and deletion will cause the index to be rebuilt, which may have serious performance impacts.

The first call to nextRecord() returns the record data from the first record in the sequence. Subsequent calls to nextRecord() return the next consecutive record's data. To return the record data from the previous consecutive from any given point in the enumeration, call previousRecord(). On the other hand, if after creation, the first call is to previousRecord(), the record data of the last element of the enumeration will be returned. Each subsequent call to previousRecord() will step backwards through the sequence.

Final note, to do record store searches, create a RecordEnumeration with no RecordComparator, and an appropriate RecordFilter with the desired search criterion.


Method Summary
 void destroy()
          Frees internal resources used by this RecordEnumeration.
 boolean hasNextElement()
          Returns true if more elements exist in the next direction.
 boolean hasPreviousElement()
          Returns true if more elements exist in the previous direction.
 boolean isKeptUpdated()
          Returns true if the enumeration keeps its enumeration current with any changes in the records.
 void keepUpdated(boolean keepUpdated)
          Used to set whether the enumeration will be keep its internal index up to date with the record store record additions/deletions/changes.
 byte[] nextRecord()
          Returns a copy of the next record in this enumeration, where next is defined by the comparator and/or filter supplied in the constructor of this enumerator.
 int nextRecordId()
          Returns the recordId of the next record in this enumeration, where next is defined by the comparator and/or filter supplied in the constructor of this enumerator.
 int numRecords()
          Returns the number of records available in this enumeration's set.
 byte[] previousRecord()
          Returns a copy of the previous record in this enumeration, where previous is defined by the comparator and/or filter supplied in the constructor of this enumerator.
 int previousRecordId()
          Returns the recordId of the previous record in this enumeration, where previous is defined by the comparator and/or filter supplied in the constructor of this enumerator.
 void rebuild()
          Request that the enumeration be updated to reflect the current record set.
 void reset()
          Returns the enumeration index to the same state as right after the enumeration was created.
 



Method Detail

numRecords

int numRecords()
Returns the number of records available in this enumeration's set. That is, the number of records that have matched the filter criterion. Note that this forces the RecordEnumeration to fully build the enumeration by applying the filter to all records, which may take a non-trivial amount of time if there are a lot of records in the record store.

Returns:
the number of records available in this enumeration's set. That is, the number of records that have matched the filter criterion.

nextRecord

byte[] nextRecord()
                  throws InvalidRecordIDException,
                         RecordStoreNotOpenException,
                         RecordStoreException
Returns a copy of the next record in this enumeration, where next is defined by the comparator and/or filter supplied in the constructor of this enumerator. The byte array returned is a copy of the record. Any changes made to this array will NOT be reflected in the record store. After calling this method, the enumeration is advanced to the next available record.

Returns:
the next record in this enumeration.
Throws:
InvalidRecordIDException - when no more records are available. Subsequent calls to this method will continue to throw this exception until reset() has been called to reset the enumeration.
RecordStoreNotOpenException - if the record store is not open.
RecordStoreException - if a general record store exception occurs.

nextRecordId

int nextRecordId()
                 throws InvalidRecordIDException
Returns the recordId of the next record in this enumeration, where next is defined by the comparator and/or filter supplied in the constructor of this enumerator. After calling this method, the enumeration is advanced to the next available record.

Returns:
the recordId of the next record in this enumeration.
Throws:
InvalidRecordIDException - when no more records are available. Subsequent calls to this method will continue to throw this exception until reset() has been called to reset the enumeration.

previousRecord

byte[] previousRecord()
                      throws InvalidRecordIDException,
                             RecordStoreNotOpenException,
                             RecordStoreException
Returns a copy of the previous record in this enumeration, where previous is defined by the comparator and/or filter supplied in the constructor of this enumerator. The byte array returned is a copy of the record. Any changes made to this array will NOT be reflected in the record store. After calling this method, the enumeration is advanced to the next (previous) available record.

Returns:
the previous record in this enumeration.
Throws:
InvalidRecordIDException - when no more records are available. Subsequent calls to this method will continue to throw this exception until reset() has been called to reset the enumeration.
RecordStoreNotOpenException - if the record store is not open.
RecordStoreException - if a general record store exception occurs.

previousRecordId

int previousRecordId()
                     throws InvalidRecordIDException
Returns the recordId of the previous record in this enumeration, where previous is defined by the comparator and/or filter supplied in the constructor of this enumerator. After calling this method, the enumeration is advanced to the next (previous) available record.

Returns:
the recordId of the previous record in this enumeration.
Throws:
InvalidRecordIDException - when no more records are available. Subsequent calls to this method will continue to throw this exception until reset() has been called to reset the enumeration.

hasNextElement

boolean hasNextElement()
Returns true if more elements exist in the next direction.

Returns:
true if more elements exist in the next direction.

hasPreviousElement

boolean hasPreviousElement()
Returns true if more elements exist in the previous direction.

Returns:
true if more elements exist in the previous direction.

reset

void reset()
Returns the enumeration index to the same state as right after the enumeration was created.


rebuild

void rebuild()
Request that the enumeration be updated to reflect the current record set. Useful for when a MIDlet makes a number of changes to the record store, and then wants an existing RecordEnumeration to enumerate the new changes.

See Also:
RecordEnumeration.keepUpdated(boolean)

keepUpdated

void keepUpdated(boolean keepUpdated)
Used to set whether the enumeration will be keep its internal index up to date with the record store record additions/deletions/changes. Note that this should be used carefully due to the potential performance problems associated with maintaining the enumeration with every change.

Parameters:
keepUpdated - If true, the enumerator will keep its enumeration current with any changes in the records of the record store. Use with caution as there are possible performance consequences. If false the enumeration will not be kept current and may return recordIds for records that have been deleted or miss records that are added later. It may also return records out of order that have been modified after the enumeration was built. Note that any changes to records in the record store are accurately reflected when the record is later retrieved, either directly or through the enumeration. The thing that is risked by setting this parameter false is the filtering and sorting order of the enumeration when records are modified, added, or deleted.
See Also:
RecordEnumeration.rebuild()

isKeptUpdated

boolean isKeptUpdated()
Returns true if the enumeration keeps its enumeration current with any changes in the records.

Returns:
true if the enumeration keeps its enumeration current with any changes in the records.

destroy

void destroy()
Frees internal resources used by this RecordEnumeration. MIDlets should call this method when they are done using a RecordEnumeration. If a MIDlet tries to use a RecordEnumeration after this method has been called, it will throw a IllegalStateException.






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