How to code "check button"

Hello,
I am not sure if this is a right place for my question, but i will be thankful if u answer it.
I am making desktop application calling "Pharmacy application" in NetBeans. Since I am amateur, this is a simple application, with these functions:
-log in
-products
-product sell
-product purchase
-recipes
...etc.

My big problem is to code product sell. The idea is when user type product ID in text area and when he click at check button, he will get information if there is such product in database and he shows him in table (jTable), and if there is not to, it will show the message "There is no product...".
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