SOLID - Single Responsibility Principle

/* Single Responsibility Principle */

// Before
class Employee {

    private final String firstName;
    private final String lastName;

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

    public String getFirstName() {
        return firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public BigDecimal calculatePay() {
        // Take taxes, bonuses, overtime etc. on board
        return new BigDecimal("");
    }

}

// After
class Employee {

    private final String firstName;
    private final String lastName;

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

    public String getFirstName() {
        return firstName;
    }

    public String getLastName() {
        return lastName;
    }

}

class PayCalculator {

    public BigDecimal calculatePay(Employee employee) {
        // Calculate pay and take taxes, bonuses, overtime etc. on board
        return new BigDecimal("");
    }

}