So what it means is you are talking to a variable in a nested (or nested like class - in this case the lamda expression) that isnt set to final or still acts as a final variable.
You have 2 options. The first is to put the variables outside the function, making it a field variable. The other option is to create another variable just before the lamda and set that new variable as the variables before.
Please note that these are java specific issues and I would advise understanding java before you takle the sponge api.