Developer.java

public class Developer {
  
  private Role role;
  
  public double getSalary() {
      switch(this.role) {
          case TRAINEE:
              return 500;
          case JUNIOR:
              return 1000;
          case EXPERT:
              return 2000;
          case SENIOR:
              return 4000;
          default:
              throw new RoleException("Invalid role.");
      }
  }
  
  public boolean promote() {
      switch(this.role) {
          case TRAINEE:
              this.role = Role.JUNIOR;
              break;
          case JUNIOR:
              this.role = Role.EXPERT;
              break;
          case EXPERT:
              this.role = Role.SENIOR;
              break;
          default:
              return false;
      }
      return true;
  }
  
  ...
  
}