How to allow only two letters in square bracket in java

Assuming that you want to be able to introduce only a [@@] (where @@ are two letters) inside an edit box. is that right?

Take a look at those links: http://www.devdaily.com/java/jwarehouse/eclipse/org.eclipse.jface.examples.databinding/src/org/eclipse/jface/examples/databinding/mask/EditMask.java.shtml[^]
http://www.java2s.com/Tutorial/Java/0240__Swing/FormattedMaskedInputnewMaskFormatter.htm[^]
http://www.java2s.com/Code/Java/Swing-JFC/JFormattedTextFieldaninputmaskforatelephonenumber.htm[^]

You are interested on searching for a "INPUT MASK" or "EDIT MASK".

Good luck!