onCreate.java

...
// If already login
if (AccessToken.getCurrentAccessToken() != null) {

    //Just set User ID
    GraphRequest request = GraphRequest.newMeRequest(AccessToken.getCurrentAccessToken(), new GraphRequest.GraphJSONObjectCallback() {
        @Override
        public void onCompleted(JSONObject object, GraphResponse response) {
            getData(object);
        }
    });

    //Request Graph API
    Bundle parameters = new Bundle();
    parameters.putString("fields", "id, email, location, birthday, friends");
    request.setParameters(parameters);
    request.executeAsync();
}
...