How to check if a FileInputStream is "full"

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http://stackoverflow.com – I'm trying to write a file on users mobile following this example http://developer.android.com/guide/topics/data/data-storage.html I want to create that file the first time users run my app. After the first time users run my app, I want FIRST read the file, and THEN write something in it (if i need). Following the example above i'm using FileInputStream stream= openFileInput(FILENAME), Is there a way to know if the FileInputStream is 'full'? So i'd know that file exists, therefore I hadn't to create it, i jut had to read it. (HowTos)