aa.java

 private void addListenerForChatRoomStillExits() {
        String currentUserId = SessionManager.getInstance().getString(Constant.FIREBASE_CURRENT_USER_ID);
        userDatabase.child("users").child(currentUserId).child("conversations").orderByChild("isAccepted").equalTo(true).addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                boolean isRoomExits = false;
                if (dataSnapshot.exists()) {
                    for (DataSnapshot data : dataSnapshot.getChildren()) {
                        Object object = data.getValue();
                        HashMap lastMap = (HashMap) object;
                        if (lastMap.get("location").equals(location)) {
                            isRoomExits = true;
                            break;
                        }
                        //...
                    }
                }
                if (!isRoomExits) {
                    Toast.makeText(getBaseContext(), "room deleted", Toast.LENGTH_LONG).show();
                }
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });
    }