A probleme with my get balance

Question

public void process(APDU apdu)
byte[]buffer = apdu.getBuffer();
if(buffer[ISO7816.OFFSET_CLA]==ISO7816.CLA_ISO7816 && buffer[ISO7816.OFFSET_INS]==ISO7816.INS_SELECT)
return;
if(buffer[ISO7816.OFFSET_CLA]!=EPURSE_CLA)
ISOException.throwIt(ISO7816.SW_CLA_NOT_SUPPORTED);
short amount=(short)0;
switch(buffer[ISO7816.OFFSET_INS])
//debit
case EPURSE_ADD:
apdu.setIncomingAndReceive();
amount=Util.getShort(buffer,ISO7816.OFFSET_CDATA);
balance += amount;
break;
//credit
case EPURSE_SUB:
apdu.setIncomingAndReceive();
amount=Util.getShort(buffer,ISO7816.OFFSET_CDATA);
balance -= amount;
break;
//balance
case EPURSE_BAL:
Util.setShort(buffer,ISO7816.OFFSET_CDATA,balance);
apdu.setOutgoingAndSend(ISO7816.OFFSET_CDATA,(short)2);
break;
default:
ISOException.throwIt(ISO7816.SW_INS_NOT_SUPPORTED);
mydemo.src with a kit java card:
CLA: 00, INS: a4, P1: 04, P2: 00, Lc: 0a, a0, 00, 00, 00, 62, 03, 01, 0c, 03, 01, Le: 00, SW1: 90, SW2: 00
CLA: c0, INS: b0, P1: 00, P2: 00, Lc: 02, 00, 80, Le: 00, SW1: 90, SW2: 00
CLA: c0, INS: b2, P1: 00, P2: 00, Lc: 02, 00, 20, Le: 00, SW1: 90, SW2: 00
CLA: c0, INS: b4, P1: 00, P2: 00, Lc: 00, Le: 02, 00, 60, SW1: 90, SW2: 00
please can you help me

Answer 1

My lucky guess would be:
case EPURSE_BAL:
Util.setShort(buffer,(short)0,balance);
apdu.setOutgoingAndSend((short)0,(short)2);
Propably your APDU has no data part and you get an ArrayIndexOutOfBounds exception.
By the way how about using the following line?
if (applet.select()) return;