The RecordComparator interface is used to compare two records to determine their sorting order. It defines a compare method that returns an integer indicating if the first record precedes, follows, or is equivalent to the second record. The compare method is called by RecordEnumeration to sort records in an application-specified order when retrieving records from a record store.

1. Interface RecordComparator
Interface RecordComparator

2. • javax.microedition.rms
• public interface RecordComparator
Interface RecordComparator

3. • It is used to comparing two records. Generally it is used to
find the sorting order.
• The return value must indicate the ordering of the two
records.
• The compare method is called by RecordEnumeration to
sort and return records in an application specified order.
For example:
• RecordComparator c = new AddressRecordComparator(); if
(c.compare(recordStore.getRecord(rec1),
recordStore.getRecord(rec2)) ==
RecordComparator.PRECEDES) return rec1;
Interface RecordComparator

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import javax.microedition.rms.*;
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
import java.io.*;
public class MSortRec extends MIDlet implements CommandListener
{
private Display d;
private Alert a;
private Form f;
private Command exit;
private Command start;
private RecordStore rec = null;
private RecordEnumeration r = null;
private Comparator2 com = null;
Interface RecordComparator

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public MSortRec ()
{
d = Display.getDisplay(this);
exit = new Command("Exit", Command.SCREEN, 1);
start = new Command("Start", Command.SCREEN, 1);
f = new Form("Mixed RecordEnumeration");
f.addCommand(exit);
f.addCommand(start);
f.setCommandListener(this);
}
Interface RecordComparator

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public void startApp()
{
d.setCurrent(f);
}
public void pauseApp()
{
}
public void destroyApp( boolean unconditional )
{
}
public void commandAction(Command c, Displayable dd)
{
if (c == exit)
{
destroyApp(true);
notifyDestroyed();
}
Interface RecordComparator

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else if (c == start)
{
try
{
rec = RecordStore.openRecordStore("myRecordStore", true );
}
catch (Exception er)
{
a = new Alert("Error Creating",
er.toString(), null, AlertType.WARNING);
a.setTimeout(Alert.FOREVER);
d.setCurrent(a);
}
Interface RecordComparator

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try
{
//byte[] outputRecord;
byte[] by;
String s[] = {"Sita", "Rama", "Anand"};
int i[] = {15, 10, 5};
//ByteArrayOutputStream outputStream =
ByteArrayOutputStream baos =
new ByteArrayOutputStream();
//DataOutputStream outputDataStream =
DataOutputStream ods =
new DataOutputStream(baos);
Interface RecordComparator

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for (int x = 0; x < 3; x++)
{
ods.writeUTF(s[x]);
ods.writeInt(i[x]);
ods.flush();
by = baos.toByteArray();
rec.addRecord(by, 0,by.length);
baos.reset();
}
baos.close();
ods.close();
}
catch ( Exception error)
{
a = new Alert("Error Writing",
error.toString(), null, AlertType.WARNING);
a.setTimeout(Alert.FOREVER);
d.setCurrent(a);
}
Interface RecordComparator

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try
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String[] s = new String[3];
int z = 0;
byte[] by = new byte[300];
ByteArrayInputStream bais =
new ByteArrayInputStream(by);
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DataInputStream dis =
new DataInputStream(bais);
StringBuffer sb = new StringBuffer();
com = new Comparator2();
r= rec.enumerateRecords(null, com, false);//now RecordEnumeration is build
while (r.hasNextElement())//if there is another record is there in RecordEnumeration, returns true,
//false otherwise
{
rec.getRecord( r.nextRecordId(),by, 0);//it returns the record ID of next record
//present in the RecordEnumeration and copies into by array
sb.append(dis.readUTF());
sb.append(dis.readInt());
sb.append("n");
dis.reset();
}
Interface RecordComparator

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a = new Alert("Reading", sb.toString(), null,
AlertType.WARNING);
a.setTimeout(Alert.FOREVER);
d.setCurrent(a);
dis.close();
bais.close();
}
catch (Exception error)
{
a = new Alert("Error Reading",
error.toString(), null, AlertType.WARNING);
a.setTimeout(Alert.FOREVER);
d.setCurrent(a);
}
Interface RecordComparator

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try
{
rec.closeRecordStore();
}
catch (Exception er)
{
a = new Alert("Error Closing",
er.toString(), null, AlertType.WARNING);
a.setTimeout(Alert.FOREVER);
d.setCurrent(a);
}
Interface RecordComparator

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if (RecordStore.listRecordStores() != null)
{
try
{
rec.deleteRecordStore("myRecordStore");
com.compareClose();
r.destroy();
}
catch (Exception er)
{
a = new Alert("Error Removing",
er.toString(), null, AlertType.WARNING);
a.setTimeout(Alert.FOREVER);
d.setCurrent(a);
}
}
}
}
}
Interface RecordComparator

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class Comparator2 implements RecordComparator
{
private byte[] comparatorInputData = new byte[300];
private ByteArrayInputStream comparatorInputStream = null;
private DataInputStream comparatorInputDataType = null;
public int compare(byte[] record1, byte[] record2)
{
int record1int, record2int;
try
{
int maxlen = Math.max(record1.length, record2.length);
if (maxlen > comparatorInputData.length)
{
comparatorInputData = new byte[maxlen];
}
Interface RecordComparator

15. • comparatorInputStream = new
ByteArrayInputStream(record1);
• comparatorInputDataType =
• new DataInputStream(comparatorInputStream);
• comparatorInputDataType.readUTF();
• record1int = comparatorInputDataType.readInt();
• comparatorInputStream = new
ByteArrayInputStream(record2);
• comparatorInputDataType =
• new DataInputStream(comparatorInputStream);
• comparatorInputDataType.readUTF();
• record2int = comparatorInputDataType.readInt();
Interface RecordComparator

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if (record1int == record2int)
{
return RecordComparator.EQUIVALENT;
}
else if (record1int < record2int)
{
return RecordComparator.PRECEDES;
}
else
{
return RecordComparator.FOLLOWS;
}
}
catch (Exception error)
{
return RecordComparator.EQUIVALENT;
}
}
Interface RecordComparator

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public void compareClose()
{
try
{
if (comparatorInputStream!= null)
{
comparatorInputStream.close();
}
if (comparatorInputDataType!= null)
{
comparatorInputDataType.close();
}
}
catch (Exception error)
{
}
}
}
Interface RecordComparator

18. • For java tutorials visit:
http://improvejava.blogspot.in
Interface RecordComparator