In JCreator you only have a debugger on the posh paid-for version, which you can try free of charge for a month.
If you have the LE version like me, you will have to follow Justin Fox's suggestion.
Look at this method which is supposed to add the sum of successive numbers (those who know a little arithmetic will remember this is not an efficient method to do this, and the more eagle-eyed Ranch members will see the reason for the out-by-one error before trying the method);
Now, if you set it up with 0, 10, your printout reads 0 1 2 3 4 5 6 7 8 9. At this point you can see how the out-by-one error occurs. The //test bit allows you to use ctrl-F to locate all such
testing code and delete it (or, for an assessment, to comment it out and show what you were up to).
The JOptionPane in the constructor is a modal dialogue; it stops processing until you click its "OK" button, so you can halt processing wherever you wish.
So, using these display methods allows you
to follow the flow of code by showing line numbers or method names,to allow methods to run freely, if you don't put any messages in them,and (probably most important of all), to see the values of variables and objects during the flow of processing. I hope this is of some help.
CR