Designing the Database Schema

In the low level design of the payment app, one crucial step is designing the database schema. The database schema represents the structure of the payment app's database and defines the relationships between different entities.

To design the database schema, we need to consider the requirements of the payment app and identify the entities that need to be stored in the database. For example, the payment app might have entities such as User, PaymentMethod, Transaction, and Discount.

Once we have identified the entities, we can define the attributes and relationships for each entity. For example, the User entity might have attributes such as ID, Name, and Email, and a relationship with the PaymentMethod entity indicating that a user can have multiple payment methods.

Here's an example of a database schema for the payment app:

1User Table:
2+----+--------------+------------------+
3| ID |     Name     |      Email       |
4+----+--------------+------------------+
5| 1  | John Doe     | john@example.com |
6| 2  | Jane Smith   | jane@example.com |
7+----+--------------+------------------+
8
9PaymentMethod Table:
10+----+---------+----------------+---------+
11| ID | User_ID |    Method      | Default |
12+----+---------+----------------+---------+
13| 1  | 1       | Credit Card    |    1    |
14| 2  | 1       | Debit Card     |    0    |
15| 3  | 2       | PayPal         |    1    |
16+----+---------+----------------+---------+
17
18Transaction Table:
19+----+---------------+-------------+---------------------+
20| ID | User_ID       | Amount      |    Timestamp        |
21+----+---------------+-------------+---------------------+
22| 1  | 1             | 100.00      | 2022-01-01 10:00:00 |
23| 2  | 2             | 50.00       | 2022-01-02 15:30:00 |
24+----+---------------+-------------+---------------------+

This database schema reflects the relationships between the User, PaymentMethod, and Transaction entities. The User table has a primary key column (ID) and the PaymentMethod table has a foreign key column (User_ID) that references the ID column in the User table. Similarly, the Transaction table has a foreign key column (User_ID) that references the ID column in the User table.

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class Main {

    public static void main(String[] args) {

    // replace with your Java logic here

    for(int i = 1; i <= 100; i++) {

      if(i % 3 == 0 && i % 5 == 0) {

          System.out.println("FizzBuzz");

      } else if(i % 3 == 0) {

          System.out.println("Fizz");

      } else if(i % 5 == 0) {

          System.out.println("Buzz");

      } else {

          System.out.println(i);

      }

    }    

  }

}