Need help about the SHA Message Digest ? & what is use of Message Diagest ?

Question

need help about the SHA Message Digest ? & what is use of Message Diagest ?
1>i have one program of making message digest
2>which requires two files name
3>one for input like txt
4> second is out put file of message digest
can any one tell what is the use of second generated file .

Answer 1

MessageDigest md = MessageDigest.getInstance("SHA");
FileInputStream fis = new FileInputStream(args[0]);
byte[] b = new byte[1024];
int readed = -1;
while((readed = fis.read(b)) > 0)
     md.update(b, 0, readed);
fis.close();
FileOutputStream fos = new FileOutputStream(args[1]);
byte[] d = md.digest();
StringBuffer sb = new StringBuffer();
for(int i = 0; i < d.length; i++) {
     String str = Integer.toHexString(d[i] & 0xff);
     sb.append(str.length() < 2 ? "0" + str : str);
fos.write(sb.toString().getBytes());
fos.close();