in java using postgresql

im trying to take a number from one of my tables and then add it to the new user input but im having some trouble .

public Bank deposit(double account_balance) { try(Connection conn = ConnectionUt.getConnection()){ String sql = "SELECT * FROM bank_account WHERE account_balance = " + account_balance + ";"; Statement statement = conn.createStatement(); List list = new ArrayList<>(); ResultSet result = statement.executeQuery(sql); Bank bank = new Bank(); bank.setAccountBalance(result.getDouble("account_balance")); list.add(bank); bank = bank + account_balance; }catch (SQLException e){ e.printStackTrace(); } return null; }