Number of ways to display the messages in SAP

Number of ways to display the messages.
1). MESSAGE 'abs' type 'I'.
2). MESSAGE I002 (<Message Class>)
            In the message class we have to write the corresponding message for 002.
3). REPORT <Program Name> MESSAGE-ID <Message Class>.
        MESSAGE I002.
            In the message class we have to write the corresponding message for 002.
4). MESSAGE i006 WITH text-003.
                    In the text symbols 003 we have to write the corresponding message.
5). MESSAGE text-001 type 'I'.
                        In the text symbols 001 we have to write the corresponding message.
6). MESSAGE i006 WITH 'Invalid purchase order Number'(003).
       006 message description is sending at runtime, in the message class we mention & & & & for the corresponding 006 number. In the text symbols 003 we are writing the description, it    just for our display purpose.
7). MESSAGE ID '<Message Class>' type 'I' NUMBER 002.
8). MESSAGE i003 (<Message Class>) WITH '<Some text message> '.
9). MESSAGE i003 (<Message Class>) WITH text-003.
                        In the text symbols 003 we have to write the corresponding message.
10). MESSAGE i003 (<Message Class>) with p_user.

Simplest way to use Message Class and Concatenate with Some Variable in SAP Report:
I have used & Symbol to Concatenate variable with Message so that while displaying the message   we can replace & value with some particular value.