Messages SE91 msg class

Refer:
1. http://abaplovers.blogspot.com/2008/02/displaying-messages-in-abap.html
2. http://www.abapprogramming.net/2009/02/syntax-for-message.html

eg:
MESSAGE E010 WITH 'Example' SY-UNAME.

1. MESSAGE xnnn.
2. MESSAGE ID id TYPE mtype NUMBER n.
3. MESSAGE xnnn(mid).

There are six kinds of message type:
A (Abend)
Termination
E (Error)
Error
I (Info)
Information
S (Status)
Status message
W (Warning)
Warning
X (Exit)
Termination with short dump
See the syntax shown below for displaying a message in your programs.

MESSAGE ID id TYPE mtype NUMBER n.

ID
message class in our case ZEXERCISE1 or ZEXERCISE2
TYPE
message type (A,E,I,S,W,X)
NUMBER
message number
Example

MESSAGE ID 'ZEXERCISE' TYPE 'S' NUMBER '000'.