Java Card "Hello World" Applet

In the example below, java card ” Hello World”  applet  is demonstrated.  The applet flow is that when a user sends a specific APDU to the applet then it will return ‘Hello Word’ to the off-card application or CAD. Firstly, we will test it on JCOP shell and later will write a off-card application which will display word ‘Hello World’.

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package helloWorldPackage; import javacard.framework.APDU; import javacard.framework.Applet; import javacard.framework.ISO7816; import javacard.framework.ISOException; import javacard.framework.Util; public class HelloWorldApplet extends Applet {          private static final byte[] helloWorld = {(byte)'H',(byte)'e',(byte)'l',(byte)'l',(byte)'o',(byte)' ',(byte)'W',(byte)'o',(byte)'r',(byte)'l',(byte)'d',};          private static final byte HW_CLA = (byte)0x80;          private static final byte HW_INS = (byte)0x00;          public static void install(byte[] bArray, short bOffset, byte bLength) {              new HelloWorldApplet().register(bArray, (short) (bOffset + 1), bArray[bOffset]);          }          public void process(APDU apdu) {              if (selectingApplet()) {              return;          }          byte[] buffer = apdu.getBuffer();          byte CLA = (byte) (buffer[ISO7816.OFFSET_CLA] & 0xFF);          byte INS = (byte) (buffer[ISO7816.OFFSET_INS] & 0xFF);          if (CLA != HW_CLA)         {             ISOException.throwIt(ISO7816.SW_CLA_NOT_SUPPORTED);         }           switch ( INS ) {              case HW_INS:                getHelloWorld( apdu );                break;             default:                ISOException.throwIt(ISO7816.SW_INS_NOT_SUPPORTED);          }    }   private void getHelloWorld( APDU apdu)   {       byte[] buffer = apdu.getBuffer();       short length = (short) helloWorld.length;       Util.arrayCopyNonAtomic(helloWorld, (short)0, buffer, (short)0, (short) length);       apdu.setOutgoingAndSend((short)0, length);   } }

Output on JcopShell:

 First we need to select the newly installed applet
 => 00 A4 04 00 0E 48 65 6C 6C 6F 57 6F 72 6C 64 2E    .....HelloWorld.
 61 70 70 00                                        app.
 (491682 nsec)
 <= 90 00                                              ..
 Status: No Error

 Sending command with correct CLA and INS which will return Hellow World
 in hex format
 cm>  /send 8000000000
 => 80 00 00 00 00                                     .....
 (556774 nsec)
 <= 48 65 6C 6C 6F 20 57 6F 72 6C 64 90 00             Hello World..
 Status: No Error

 Sending APDU with wrong CLA which results in 6E00 (CLA value not support 
 ed)
 cm>  /send 0000000000
 => 00 00 00 00 00                                     .....
 (2417 usec)
 <= 6E 00                                              n.
 Status: CLA value not supported