定义四个类，分别为Employee类、SalariedEmployee类、HourlyEmployee类和CommissionEmployee类。其中Employee类是其他三个类的父类。Employee类包含姓名和身份证号。除此之外，SalariedEmployee类还应包含每月工资；HourlyEmployee类还应包含每小时工资数和工作时间数；CommissionEmployee还应包含提成比例和销售总额。其中HourlyEmployee的工资为：每小时工资数×工作时间数，CommissionEmployee的工资为：提成比例×销售总额。每个类都应有合适的构造方法、数据成员的设置和读取方法。注意：子类有时需调用父类的构造方法和被覆盖的方法，成员变量定义为private，对有些方法实现重载。

以下是四个类的定义：

## Employee类

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

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

    public String getName() {
        return this.name;
    }

    public String getId() {
        return this.id;
    }
}

## SalariedEmployee类

public class SalariedEmployee extends Employee {
    private double monthlySalary;

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

    public double getMonthlySalary() {
        return this.monthlySalary;
    }

    public void setMonthlySalary(double monthlySalary) {
        this.monthlySalary = monthlySalary;
    }

    public double getSalary() {
        return this.monthlySalary;
    }
}

## HourlyEmployee类

public class HourlyEmployee extends Employee {
    private double hourlySalary;
    private int workHours;

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

    public double getHourlySalary() {
        return this.hourlySalary;
    }

    public void setHourlySalary(double hourlySalary) {
        this.hourlySalary = hourlySalary;
    }

    public int getWorkHours() {
        return this.workHours;
    }

    public void setWorkHours(int workHours) {
        this.workHours = workHours;
    }

    public double getSalary() {
        return this.hourlySalary * this.workHours;
    }
}

## CommissionEmployee类

public class CommissionEmployee extends Employee {
    private double commissionRate;
    private double salesTotal;

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

    public double getCommissionRate() {
        return this.commissionRate;
    }

    public void setCommissionRate(double commissionRate) {
        this.commissionRate = commissionRate;
    }

    public double getSalesTotal() {
        return this.salesTotal;
    }

    public void setSalesTotal(double salesTotal) {
        this.salesTotal = salesTotal;
    }

    public double getSalary() {
        return this.commissionRate * this.salesTotal;
    }
}

以上是四个类的定义，它们分别表示不同类型的员工。每个类都有对应的数据成员和方法，可以方便地获取员工的信息和计算员工的薪水。其中，Employee类是其他三个类的父类，包含了所有员工都具有的基本信息。其他三个类则根据不同的情况增加了一些特定的信息和方法。