What is the $P!{} Parameter , How it is used in Jasper reports

Lets suppose I have the following query,

Select L_name, 
age_1,
$P!{check} as Characteristic
from table

This paramater allows me to view the various characteristics of the person I am refering above. It would be dependent on another parameter, let us call that parameter as $P{value}. 

In the default expression of the parameter "check", I could define the following;

$P{value}==1 ? "Physical_strength" : $P{value}==2 ? "IQ": "Nature";

Depending on the various values of $P{value}, the parameter "check" will input the values into the query and mind you, the above three stated characteristics are nothing but the table columns, so basically we are displaying different columns based on the parameter "value".

For instance, the parameter "value" was entered as 2, so my running query would look like (which you can check in the logs);

select L_name, age_1, IQ as characteristics from table

Hope this explains all.

Regards,
KKriplani