Java - Splitting a string into individual letters : For a school project i need to encrypt a random Java String, for the beginning "test", with the Caesar-Code (Every letter of the alphabet is replaced with the one that is 3 places ahead, a -> c, b -> d and so on). 

So my question is: 
How can i make this happen using a jTextField (where the String to be encrypted is written) and a jButton to fire of the encyrption function ?

for me it is more important to know how i can convert the String to Individual letters than the enycrption itself because i think thats not that hard to get so i can possibly do that by myself.

Thx for help :) 