Employee: firstNamelastNamesocialSecurityNumberSalaridEmployee: weeklySalary(周薪）HourlyEmployee: wage(每小时的工钱)hours（月工作小时数）CommisionEmployee: grossSales(销售额)commissionRate(提成比率)BasePlusCommisionEmployee: baseSalary（月基本工资）Employee类中定义了抽象方法earning，用于计算员工的月工资。SalaridEmployee月工资计算为：weeklySalary4HourlyEmployee月工资计算为：wagehoursCommisionEmployee月工资计算为：grossSalescommissionRateBasePlusCommisionEmployee月工资计算为：grossSalescommissionRate+baseSalary