Java reading and then modifying binary tree and then saving changed tree to a text file -

http://pastebin.com/72sgpe4v -animalguess class

http://pastebin.com/u4rse5ue -animalnode class

so goal of program have computer guess animal thinking of , if doesn't, user adds in animal thinking of , question distinguish animal previous animal. once user chooses not continue playing, program exits. when program exits, , started again, program not remember questions user put program during previous run. need program read in text file or without binary tree data in , write out new binary tree made user text file later use. can't find right place put in write out data text file. thought after line 13 in animalguess.java keep getting errors.

i think should try iterating through contents of rootoftree after while loop ends , writing them file (right after line 14).