Data Persistency - Java 2 Micro Edition Application Development - page 138

RecordStore travelList = RecordStore.open ("travelList", true);
RecordEnumeration enumeration = travelList.enumerateRecords
(null, new JourneyDateComparator(), false);

while (enumeration.hasNext()) {
Journey journey = new Journey (enumeration.next())
// place real operations here
}
enumeration.destroy()
travelList.closeRecordStore();

You can also add methods for comparing the destination (or distance), allowing you to iterate the
records ordered correspondingly. Table 5.4 shows a general overview of the methods of the
RecordEnumeration class.

Table 5 . 4. Methods of RecordEnumeration

Name Purpose

void destroy() Releases system resources associated with this

enumeration.

boolean
hasNextElement()

Indicates whether records are left in the enumeration.

boolean
hasPreviousElement()

Analogous to hasNextElement() , but in the inverse
direction.
boolean isKeptUpdated() Indicates whether the enumeration is kept updated.
void keepUpdated
(boolean keepUpd)

Sets or resets the automatic update mode.

byte[] nextRecord() Returns the next record.
int nextRecordId() Returns the ID of the next record.
int numRecords() Returns the number of records in this enumeration. Differs
from RecordStore.getNumRecords() for filtered or
outdated enumerations only.
byte[] previousRecord() Returns the previous record.
int previousRecordId() Returns the ID of the previous record.
void rebuild() Rebuilds the enumeration to reflect all changes. Performed

automatically in the updated mode.

void reset() Resets the enumeration to the first record.

Filtered Record Enumerations

You have already seen that the enumerateRecords() method has a filter parameter, but we have
not explained how to use it. The corresponding RecordFilter interface works similarly to the
RecordComparator interface. It provides a single method, matches() , which takes a record byte
array as input and returns a boolean value, determining whether the given record passes the filter.

For example, if you need an enumeration of the journeys where the distance was greater than x
kilometers, you can implement it as follows:

Class MinDistanceFilter {
int min;
DistanceFilter (int min) {
this.min = min;
}
boolean matches (byte[] record) {
return new Journey (record).getDistance() >= min;
}