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I don't really know what you're trying to do with the Formatter. I'd recommend just using a FileOutputStream at first. What does the Formatter give you?

Hmm, maybe, it really depends on what you're doing. I don't know what Exists is, but I'm assuming that's pseudocode for a real method. What happened when you tried?

Well, you could either read the file line by line, searching each line, or you could read the whole file into a data structure of some kind, then search that. There are a ton of ways to do it, it's...

The FileOutputStream has a constructor that takes a boolean- whether the file should be overwritten or appended. That's a good google keyword, something like "java file io append" would probably get...