Java – Find out if data exists in Firebase

I’m using the following to get a username from Firebase. But in this case, how do I know if the username exists.

Firebase firebaseRef = new Firebase("<Firebasae_URL>/Users");
Query query=firebaseRef.orderByChild("username").equalTo("username");

So in your case, the code should look up the username present in the database.

Firebase firebaseRef = new Firebase("<Firebasae_URL>/Users").child("username");
firebaseRef.addListenerForSingleValueEvent(new ValueEventListener) {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        if (dataSnapshot.exists()) {
             User Exists
        }
    }

@Override
    public void onCancelled(FirebaseError firebaseError) {

}
});