J2ME in a Nutshell

Name

RecordComparator

Synopsis

This is an interface used when creating a RecordEnumeration that determines the order in which records are returned. The interface consists of the single method compare(), which is passed a pair of byte-array records, rec1 and rec2. The method returns one of the following integer values to indicate their relative ordering:

PRECEDES

Indicates that rec1 should appear before rec2

EQUIVALENT

Indicates that rec1 and rec2 are equivalent according to the sorting criterion applied by this comparator. Note that this does not imply that the records are equal, although equal records would result in this value being returned.

FOLLOWS

Indicates that rec1 should appear after rec2

A typical implementation of this method wraps each of the records with a ByteArrayInputStream and a DataInputStream so that the contents of the records can be accessed as a set of fields. To construct a filter that sorts based on the natural sorting order of the first field in the record, which is assumed to be a String, the record in the byte arrays rec1 and rec2 is converted to DataInputStreams like this:

DataInputStream dis1 = new DataInputStream(new ByteArrayInputStream(rec1));

DataInputStream dis2 = new DataInputStream(new ByteArrayInputStream(rec2));

At this point, the field to be compared is extracted from each record using the DataInputStream readUTF() method, and the comparison is performed:

int res = dis1.readUTF().compareTo(dis2.readUTF());

The return value from the method ...