dbreference = FirebaseDatabase.getInstance().getReference("Electronic").child("userid");

 dbreference.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot snapshot) {
if (snapshot.exists()) {
  // TODO: handle the case where the data exists

  for (DataSnapshot data : snapshot.getChildren()) {

        final Solditem b1 = data.getValue(SoldItem.class);

          child_count++;
          list.add(b1);
          staggeredBooksAdapter.notifyDataSetChanged();


  }
}

DatabaseReference ref = FirebaseDatabase.getInstance().getReference();
Query sellerquery = ref.child("Electronic").child("userid");

sellerquery.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
    for (DataSnapshot appleSnapshot: dataSnapshot.getChildren()) {
        appleSnapshot.getRef().removeValue();
    }
}