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 k6ž package wallet ;
import javacard.framework.*;
public class Wallet extends Applet ...
final static byte WALLET = 0xAA ;
// codes of INS byte in the command APDU header
final static byte GET = 0x01 ;
final static byte CREDIT = 0x02 ;
final static byte DEBIT = 0x03 ;
final static short MAX BALANCE = 10000 ;
final static short MAX TRANSACTION AMOUNT = 100 ;
private short balance ;
public Wallet() balance = 0 ; register() ; public static void install( APDU apdu ) new Wallet() ; public void process( APDU apdu ) byte[] buffer = apdu.getBuffer();
if ( buffer[ISO.OFFSET CLA] != WALLET )
ISOException.throwIt(ISO.SW CLA NOT SUPPORTED) ;
switch (buffer[ ISO.OFFSET INS]) case GET : getBalance(buffer); break ;
case CREDIT : credit(buffer); break ;
case DEBIT : debit(buffer); break ;
default : ISOException.throwIt(ISO.SW INS NOT SUPPORTED) ;
...
void credit( Byte[] buffer) byte byteRead = (byte) apdu.setIncomingAndReceive();
if (byteRead != 1) ISOException. throwIt( ISO.SW WRONG LENGTH) ;
short creditAmount = (buffer[ISO.OFFSET CDATA]
8)
buffer[ISO.OFFSET CDATA+1] ;
// process data
if ((creditAmount
MAX TRANSACTION AMOUNT) (creditAmount
0 ))
ISOException.throwIt (INVALID TRANSACTION AMOUNT) ;
// check the new balance
if ((balance - creditAmount)
MAX BALANCE)
ISOException.throwIt(EXCEED MAXIMUM BALANCE) ;
balance = balance - creditAmount ;
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