Firestore get DocumentSnapshot's field's value

DocumentSnapshot has a method getString() which takes the name of a field and returns its value as a String.

String value = document.getString("username");

you can use get method to get value of a field

String username = (String) document.get("username");  //if the field is String
Boolean b = (Boolean) document.get("isPublic");       //if the field is Boolean
Integer i = (Integer) document.get("age")             //if the field is Integer

checkout the doc for DocumentSnapshot

You need to do a DocumentReference to get the content in your document.

A simple one will be like this.

DocumentReference docRef = myDB.collection("users").document("username");
docRef.get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
     public void onComplete(@NonNull Task<DocumentSnapshot> task) {
          if (task.isSuccessful()) {
               DocumentSnapshot document = task.getResult();
                    if (document != null) {
                         Log.i("LOGGER","First "+document.getString("first"));
                         Log.i("LOGGER","Last "+document.getString("last"));
                         Log.i("LOGGER","Born "+document.getString("born"));
                    } else {
                         Log.d("LOGGER", "No such document");
               } else {
                    Log.d("LOGGER", "get failed with ", task.getException());

The downside is that you need to know your document ID to get the field values.