Problem to organize my code in classes
I'm just confused about how to organize my code.
Basically I have a GUI and other methods to load/write data from/into files.
For now, I just have one BIG class with everything inside but of course I know it's not that good and I would like to dispatch my code into classes.
I thought about creating one general class and put the methods that load/write files in that class and create another class just for the GUI. But actually, there are variables that I need in the load/write methods AND in the GUI too.
So, should I create this extra class for the GUI and make it "extends" the general class (where the main is, and the load/write files methods are) ? I'm not sure about this "extends", I mean if it's the right choice for my situation.
Can someone help me please ?
Thank you for your help.