When we have an entity-relationship diagram (ERD), we can convert it into a class diagram to implement in Java. The class diagram represents the structure and behavior of classes, their attributes, and methods. Let's understand the process of converting an ERD to a class diagram through an example.

Suppose we have an ERD for an Employee-Project Management system. The ERD includes two entities: Employee and Project. The Employee entity has attributes such as id and name, and a many-to-many relationship with the Project entity.

In the class diagram, we can represent the Employee entity as a Java class with the corresponding attributes and a list of Project objects. Similarly, the Project entity can be represented as a Java class with attributes such as id and name:

1import java.util.List;
2
3class Employee {
4  private int id;
5  private String name;
6  private List<Project> projects;
7
8  public Employee(int id, String name, List<Project> projects) {
9    this.id = id;
10    this.name = name;
11    this.projects = projects;
12  }
13
14  // Getters and setters
15}
16
17class Project {
18  private int id;
19  private String name;
20
21  public Project(int id, String name) {
22    this.id = id;
23    this.name = name;
24  }
25
26  // Getters and setters
27}

xxxxxxxxxx

import java.util.List;

​

class Employee {

  private int id;

  private String name;

  private List<Project> projects;

​

  public Employee(int id, String name, List<Project> projects) {

    this.id = id;

    this.name = name;

    this.projects = projects;

  }

​

  // Getters and setters

}

​

class Project {

  private int id;

  private String name;

​

  public Project(int id, String name) {

    this.id = id;

    this.name = name;

  }

​

  // Getters and setters

}