SOLID - Open/Closed Principle

/* Open/Closed Principle */

// Before
class Employee {

    public enum EmployeeType {
        DIRECTOR, SOFTWARE_ENGINEER, DESIGNER;
    }

    private final EmployeeType type;

    public Employee(EmployeeType type) {
        this.type = type;
    }

    public EmployeeType getType() {
        return type;
    }

}

class PayCalculator {

    public BigDecimal calculatePay(Employee employee) {
        BigDecimal baseSalary;
        switch (employee.getType()) {
            case DIRECTOR:
                baseSalary = new BigDecimal("300000");
                break;
            case SOFTWARE_ENGINEER:
                baseSalary = new BigDecimal("150000");
                break;
            case DESIGNER:
                baseSalary = new BigDecimal("120000");
                break;
            default:
                throw new AssertionError();
        }
        // Calculate pay here
        return new BigDecimal("");
    }

}

// After
class Employee {

    public enum EmployeeType {
        DIRECTOR(new BigDecimal("300000")),
        SOFTWARE_ENGINEER(new BigDecimal("150000")),
        DESIGNER(new BigDecimal("120000"));

        private final BigDecimal baseSalary;

        EmployeeType(BigDecimal baseSalary) {
            this.baseSalary = baseSalary;
        }

        public BigDecimal getBaseSalary() {
            return baseSalary;
        }

    }

    private final EmployeeType type;

    public Employee(EmployeeType type) {
        this.type = type;
    }

    public BigDecimal getBaseSalary() {
        return type.getBaseSalary();
    }

}

class PayCalculator {

    public BigDecimal calculatePay(Employee employee) {
        BigDecimal baseSalary = employee.getBaseSalary();
        // Calculate
        return new BigDecimal("");
    }

}