Defining Entities and Relationships

In the process of low level design, one of the crucial steps is defining entities and their relationships. Entities are the objects or concepts of the system that play a significant role in the application.

For example, in a payment app, some entities could be User, Account, Payment, and Invoice. These entities represent real-world objects that have attributes and behaviors.

Entities are connected through relationships, which define how they interact with each other. Relationships can be one-to-one, one-to-many, or many-to-many. They help establish the logical connections between entities.

To define entities and relationships in the payment app, we need to analyze the problem statement and identify the important components. We can create a class diagram to visualize the entities and their relationships.

Here is an example of how entities and their relationships can be defined in Java:

1// User Class
2public class User {
3  private String name;
4  private String email;
5  
6  // Constructor, getters, setters, and other methods
7}
8
9// Account Class
10public class Account {
11  private double balance;
12  private List<Payment> payments;
13  
14  // Constructor, getters, setters, and other methods
15}
16
17// Payment Class
18public class Payment {
19  private double amount;
20  private String recipient;
21  
22  // Constructor, getters, setters, and other methods
23}
24
25// Invoice Class
26public class Invoice {
27  private double amount;
28  private String description;
29  
30  // Constructor, getters, setters, and other methods
31}

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class Main {

  public static void main(String[] args) {

    // Replace with your Java logic here

    String firstName = "John";

    String lastName = "Doe";

    int age = 30;

    double salary = 5000.50;

    System.out.println("Name: " + firstName + " " + lastName);

    System.out.println("Age: " + age);

    System.out.println("Salary: $" + salary);

  }

}