2.某公司的雇员分为以下若干类： (1) Employee：这是所有员工总的父类。 ① 属性：员工的姓名,员工的生日月份 ② 方法：getSalary(int month) 根据参数月份来确定工资，如果该月员工过生日，则公司会额外奖励100 元。 (2) SalariedEmployee：Employee 的子类，拿固定工资的员工。 ① 属性：月薪。 (3)HourlyEmployee：Employee 的子类，按小时拿工资的员工，每月工作超出160小时的部分按照1.5 倍工资发放。 ① 属性：每小时的工资、每月工作的小时数。 (4) SalesEmployee：Employee 的子类，销售，工资由月销售额和提成率决定。 ① 属性：月销售额、提成率。 (5) BasePlusSalesEmployee：SalesEmployee 的子类，有固定底薪的销售人员，工资由底薪加上销售提成部分。 ① 属性：底薪。 要求： 创建一个Employee 数组，分别创建若干不同的Employee对象，并打印某个月的工资。 注意：要求把每个类都做成完全封装，不允许非私有化属性。

以下是实现该程序的Java代码：

public class Employee {
    private String name;
    private int birthMonth;

    public Employee(String name, int birthMonth) {
        this.name = name;
        this.birthMonth = birthMonth;
    }

    public double getSalary(int month) {
        double salary = 0;
        return salary;
    }

    public String getName() {
        return name;
    }

    public int getBirthMonth() {
        return birthMonth;
    }
}

public class SalariedEmployee extends Employee {
    private double monthlySalary;

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

    public double getSalary(int month) {
        double salary = monthlySalary;
        if (getBirthMonth() == month) {
            salary += 100;
        }
        return salary;
    }
}

public class HourlyEmployee extends Employee {
    private double hourlySalary;
    private double monthlyWorkHours;

    public HourlyEmployee(String name, int birthMonth, double hourlySalary, double monthlyWorkHours) {
        super(name, birthMonth);
        this.hourlySalary = hourlySalary;
        this.monthlyWorkHours = monthlyWorkHours;
    }

    public double getSalary(int month) {
        double salary = 0;
        if (monthlyWorkHours <= 160) {
            salary = monthlyWorkHours * hourlySalary;
        } else {
            salary = 160 * hourlySalary + (monthlyWorkHours - 160) * hourlySalary * 1.5;
        }
        if (getBirthMonth() == month) {
            salary += 100;
        }
        return salary;
    }
}

public class SalesEmployee extends Employee {
    private double monthlySales;
    private double commissionRate;

    public SalesEmployee(String name, int birthMonth, double monthlySales, double commissionRate) {
        super(name, birthMonth);
        this.monthlySales = monthlySales;
        this.commissionRate = commissionRate;
    }

    public double getSalary(int month) {
        double salary = monthlySales * commissionRate;
        if (getBirthMonth() == month) {
            salary += 100;
        }
        return salary;
    }
}

public class BasePlusSalesEmployee extends SalesEmployee {
    private double baseSalary;

    public BasePlusSalesEmployee(String name, int birthMonth, double monthlySales, double commissionRate, double baseSalary) {
        super(name, birthMonth, monthlySales, commissionRate);
        this.baseSalary = baseSalary;
    }

    public double getSalary(int month) {
        double salary = super.getSalary(month) + baseSalary;
        if (getBirthMonth() == month) {
            salary += 100;
        }
        return salary;
    }
}

public class EmployeeTest {
    public static void main(String[] args) {
        Employee[] employees = new Employee[5];
        employees[0] = new SalariedEmployee("Tom", 2, 5000);
        employees[1] = new HourlyEmployee("Jerry", 5, 100, 180);
        employees[2] = new SalesEmployee("Lucy", 8, 10000, 0.05);
        employees[3] = new BasePlusSalesEmployee("Bob", 10, 12000, 0.1, 5000);
        employees[4] = new SalariedEmployee("Alice", 12, 6000);

        int month = 8;
        for (Employee employee : employees) {
            System.out.println(employee.getName() + "的工资是：" + employee.getSalary(month));
        }
    }
}

代码解释如下：

1. 首先定义了一个 `Employee` 类作为所有员工的父类，包含了员工的姓名和生日月份两个属性，以及一个 `getSalary` 方法来计算月薪。
2. 然后分别定义了四个子类：`SalariedEmployee`、`HourlyEmployee`、`SalesEmployee` 和 `BasePlusSalesEmployee`，它们分别对应拿固定工资、按小时拿工资、销售和固定底薪的销售人员，这些子类都继承了 `Employee` 父类，并重写了 `getSalary` 方法来计算月薪。
3. 最后在 `EmployeeTest` 类中创建一个 `Employee` 类型的数组，分别创建了若干不同类型的 `Employee` 对象，并打印了某个月的工资。
4. 在计算月薪的过程中，如果员工的生日月份与给定的月份相同，则公司会额外奖励100元，这个逻辑被封装在 `getSalary` 方法中，实现了完全封装，不允许非私有化属性。