为某公司编写一个工资支付系统，用于计算某一类员工的月薪。该公司共有四类员工：领固定月薪的（SalariedEmployee）；计时取酬的（HourlyEmployee，如果一月工时超过160小时，则还需对额外的工时支付加班费）；按销售额提成（CommissionEmployee）的和带底薪并按销售额提成的（BasePlusCommissionEmployee），其继承层次结构如下所示。已知每类员工均有表示员工工号、姓名和出生年月的属性，和用于计算员工月薪的方法。创建一个Employee变量数组，保存Employee类层次结构中每个具体类对象的引用，对每个Employee显示其工号、姓名、出生年月和月收入，如果当月是Employee的生日所在的月份，则还另发给他100元作为红包

以下是Java代码实现：

import java.util.Calendar;

public class PayrollSystemTest {
    public static void main(String[] args) {
        // 创建Employee对象数组
        Employee[] employees = new Employee[4];
        employees[0] = new SalariedEmployee("001", "John", "1990-01-01", 8000);
        employees[1] = new HourlyEmployee("002", "Tom", "1995-05-20", 20, 180);
        employees[2] = new CommissionEmployee("003", "Lucy", "1992-06-30", 10000, 0.08);
        employees[3] = new BasePlusCommissionEmployee("004", "Mike", "1985-11-15", 8000, 0.06, 2000);

        // 获取当前月份
        int currentMonth = Calendar.getInstance().get(Calendar.MONTH) + 1;

        // 遍历数组，计算月薪并输出信息
        for (Employee employee : employees) {
            System.out.println(employee.toString() +
                    ", Monthly Salary: " + employee.earnings());
            if (currentMonth == employee.getBirthdayMonth()) {
                System.out.println("Happy Birthday! You got a red packet of 100 yuan.");
            }
        }
    }
}

class Employee {
    private String id;
    private String name;
    private String birthDate;

    public Employee(String id, String name, String birthDate) {
        this.id = id;
        this.name = name;
        this.birthDate = birthDate;
    }

    public int getBirthdayMonth() {
        String[] dateArr = birthDate.split("-");
        return Integer.parseInt(dateArr[1]);
    }

    public double earnings() {
        return 0;
    }

    @Override
    public String toString() {
        return "Employee{" +
                "id='" + id + '\'' +
                ", name='" + name + '\'' +
                ", birthDate='" + birthDate + '\'' +
                '}';
    }
}

class SalariedEmployee extends Employee {
    private double monthlySalary;

    public SalariedEmployee(String id, String name, String birthDate, double monthlySalary) {
        super(id, name, birthDate);
        this.monthlySalary = monthlySalary;
    }

    @Override
    public double earnings() {
        return monthlySalary;
    }

    @Override
    public String toString() {
        return "SalariedEmployee{" +
                "monthlySalary=" + monthlySalary +
                "} " + super.toString();
    }
}

class HourlyEmployee extends Employee {
    private double wage;
    private double hours;

    public HourlyEmployee(String id, String name, String birthDate, double wage, double hours) {
        super(id, name, birthDate);
        this.wage = wage;
        this.hours = hours;
    }

    @Override
    public double earnings() {
        if (hours <= 160) {
            return wage * hours;
        } else {
            return wage * 160 + wage * 1.5 * (hours - 160);
        }
    }

    @Override
    public String toString() {
        return "HourlyEmployee{" +
                "wage=" + wage +
                ", hours=" + hours +
                "} " + super.toString();
    }
}

class CommissionEmployee extends Employee {
    private double grossSales;
    private double commissionRate;

    public CommissionEmployee(String id, String name, String birthDate, double grossSales, double commissionRate) {
        super(id, name, birthDate);
        this.grossSales = grossSales;
        this.commissionRate = commissionRate;
    }

    @Override
    public double earnings() {
        return grossSales * commissionRate;
    }

    @Override
    public String toString() {
        return "CommissionEmployee{" +
                "grossSales=" + grossSales +
                ", commissionRate=" + commissionRate +
                "} " + super.toString();
    }
}

class BasePlusCommissionEmployee extends CommissionEmployee {
    private double baseSalary;

    public BasePlusCommissionEmployee(String id, String name, String birthDate, double grossSales, double commissionRate, double baseSalary) {
        super(id, name, birthDate, grossSales, commissionRate);
        this.baseSalary = baseSalary;
    }

    @Override
    public double earnings() {
        return super.earnings() + baseSalary;
    }

    @Override
    public String toString() {
        return "BasePlusCommissionEmployee{" +
                "baseSalary=" + baseSalary +
                "} " + super.toString();
    }
}

代码中，Employee为父类，SalariedEmployee、HourlyEmployee、CommissionEmployee和BasePlusCommissionEmployee为其子类。每个子类都重写了父类的earnings方法，以计算不同类型员工的月薪。在PayrollSystemTest中创建Employee对象数组，遍历数组并调用对象方法输出信息，如果当月是员工的生日所在的月份，则输出祝福语。