EmployeeRefactored

public class Employee {
    int employeeId;
    String firstName;
    String middleName;
    String lastName;

    int experience;
    int salary;

    public Employee(String firstName, String middleName, String lastName) {
        this.firstName = firstName;
        this.middleName = middleName;
        this.lastName = lastName;
    }

    public void setSalary(int salary) {
        this.salary = salary;
    }

    public void setExperience(int experience) {
        this.experience = experience;
    }

    public void setEmployeeId(int x) {
        this.employeeId = x;
    }
}

class EmployeeBenefits {

    Employee employee;
    EmployeeBenefits(Employee employee){
        this.employee = employee;
    }

    public void calculateSalary() {
        if (employee.experience < 5) {
            employee.salary = 2000;
        }
        if (employee.experience > 5 && employee.experience < 10) {
            employee.salary = 5000;
        }
        if (employee.experience < 15) {
            employee.salary = 10000;
        }
    }

    String getDesignation() {
        if (employee.experience < 2) {
            return "D2";
        }
        if (employee.experience < 5 && employee.experience > 2) {
            return "D3";
        }
        if (employee.experience > 10) {
            return "M1";
        }
        return "CEO";
    }

    public static void main(String[] args) {
        Employee employee = new Employee("Mohandas","Karamchand","Gandhi");
        employee.setEmployeeId(1);
        employee.experience = 10;
        EmployeeBenefits benefits = new EmployeeBenefits(employee);

        System.out.println(benefits.getDesignation());
    }
}