Определяем поведение для группы элементов в enum

Пример взят из книги Effective Java

// The strategy enum pattern
enum PayrollDay {
    MONDAY(PayType.WEEKDAY), 
    TUESDAY(PayType.WEEKDAY),
    WEDNESDAY(PayType.WEEKDAY), 
    THURSDAY(PayType.WEEKDAY),
    FRIDAY(PayType.WEEKDAY),
    SATURDAY(PayType.WEEKEND), 
    SUNDAY(PayType.WEEKEND);
    
    private final PayType payType;
    
    PayrollDay(PayType payType) { this.payType = payType; }
    
    double pay(double hoursWorked, double payRate) {
        return payType.pay(hoursWorked, payRate);
    }
    
    // The strategy enum type
    private enum PayType {
        WEEKDAY {
            double overtimePay(double hours, double payRate) {
                return hours <= HOURS_PER_SHIFT ? 0 :
                (hours - HOURS_PER_SHIFT) * payRate / 2;
            }
        },
        WEEKEND {
            double overtimePay(double hours, double payRate) {
                return hours * payRate / 2;
            }
        };
        
        private static final int HOURS_PER_SHIFT = 8;
        
        abstract double overtimePay(double hrs, double payRate);
        
        double pay(double hoursWorked, double payRate) {
            double basePay = hoursWorked * payRate;
            return basePay + overtimePay(hoursWorked, payRate);
        }
    }
}