When to refactoring

BonusCalculator.java

public class BonusCalculator {

    public double getBonus(Employee employee) {
        if( employee.department == Department.IT ) {
            if(employee.year >= 5) {
                return 0.5 * employee.salary;
            }
            return 0;
        } else {
            return 1000 + 500 * employee.salary;
        }
    }

}

BonusCalculator2.java

public class BonusCalculator {

    public double getBonus(Employee employee) {
        switch (employee.department) {
            case IT:
                if (employee.year >= 5) {
                    return 0.5 * employee.salary;
                }
                return 0;
            case Sales:
                return 1000 + 500 * employee.salary;
            default:
                return 0;
        }
    }

}

BonusCalculator3.java

public class BonusCalculator {

    public double getBonus(Employee employee) {
        switch (employee.department) {
            case IT:
                if (employee.year >= 5) {
                    return 0.5 * employee.salary;
                }
                return 0;
            case Sales:
                return 1000 + 500 * employee.salary;
            case Production:
                return 0;
            case Accounting:
                return 0;
            case Legal:
                return 0;
            case HR:
                return 0;
            default:
                return 0;
        }
    }

}

CalculationStrategy.java

interface CalculationStrategy {
    double calculate(Employee employee);
}

class ITBonusCalculation implements  CalculationStrategy {

    @Override
    public double calculate(Employee employee) {
        return 0;
    }
}


class SalesBonusCalculationStrategy implements CalculationStrategy {

    @Override
    public double calculate(Employee employee) {
        return 0;
    }
}