Display warnings and error messages within a GUI on the fly

I'm creating several classes to be used together with a GUI.Within the classes I have many checks that generate warnings and error that I want to show up in message window placed within the GUI as soon as they are generated. This messagewindow is a integrated part of the GUI, and stores messages, and is also possible to scroll within to check warning/error history.

Is there a way to use listeners to trigger an update of my text box located in this GUI, or some otherway to keep track of warnings generated.

Of course the lastwarn give you the string in the warning, but I can't find a way to keep track of when the warning was generated. I have considered making a class, with some listeners, but is very uncertain what is the best way to solve this problem.