Effective Java Item 30: 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);  
   }  
   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 hours, double payRate);  
     double pay(double hoursWorked, double payRate){  
       double basePay = hoursWorked * payRate;  
       return basePay + overtimePay(hoursWorked, payRate);  
     }  
   }  
 }  
 public class StrategyEnumPattern{  
   public static void main(String[] args){  
     for (PayrollDay payrollDay : PayrollDay.values()){  
       System.out.println(payrollDay + " pays " + payrollDay.pay(9, 100));  
     }  
   }  
 }