The Fifth Class（上）

假设某公司有两类员工：一类是按销售额提成的员工，可以作为父类，另一类是带底薪加销售额提成的员工。

下面讨论两种员工之间的关系，分为5个例子来讨论。

第一个例子

声明类CommissionEmployee，继承类Object，并将姓名、工号、提成率和总销售额声明为private 实例变量。

public class CommissionEmployee {
    private String name;
    private String ID;
    private double grossSales;//销售额
    private double commissionRate;//提成率

    public CommissionEmployee(String name, String ID, double sales, double rate) {
        this.name = name;
        this.ID = ID;
        setGrossSales(sales);
        setCommissionRate(rate);
    }

    //================== getter和setter =================//
    public String getName() {return name;}
    public void setName(String name) {this.name = name;}

    public String getID() {return ID;}
    public void setID(String ID) {this.ID = ID;}

    public double getGrossSales() {return grossSales;}
    public void setGrossSales(double grossSales) {
        this.grossSales = grossSales < 0.0 ? 0.0 : grossSales;
    }

    public double getCommissionRate() {return commissionRate;}
    public void setCommissionRate(double Rate) {
        this.commissionRate = (Rate > 0.0 && Rate < 1.0) ? Rate : 0.0;
    }
    //================== getter和setter =================//

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

    public String toString() {
        return String.format("%s:%s\n%s:%s\n%s:%.2f\n%s:%.2f\n",
                "员工姓名", name, "员工工号", ID, 
                "销售额", grossSales, "提成率", commissionRate);
    }
}

测试类

public class CommissionEmployeeTest {
    public static void main(String[] args) {
        CommissionEmployee employee =
                new CommissionEmployee("小石榴","891",100000,.06);
        System.out.println("员工基本情况如下：\n");
        System.out.printf("%s %s\n", "员工姓名",employee.getName());
        System.out.printf("%s %s\n", "员工工号", employee.getID());
        System.out.printf("%s %.2f\n", "销售额", employee.getGrossSales());
        System.out.printf("%s %.2f\n", "提成率 ",employee.getCommissionRate());
        System.out.printf("%s %.2f\n", "员工工资",employee.earnings());
        employee.setGrossSales(500);
        employee.setCommissionRate(.1);
        System.out.printf("\n%s:\n\n%s","更新以后员工信息", employee);//这里对象employee直接用字符串输出
        System.out.printf("%s %.2f\n", "员工工资",employee.earnings());
    }
}

第二个例子

声明类BasePlusCommissionEmployee，继承类Object，并将姓名、工号、提成率、总销售额和底薪声明为private实例变量。
这个类的每行语句都是自己编写的，如果从类CornrnissionEmployee继承，则创建这个类的效率将大大提高。

第三个例子

声明类BasePlusCornrnissionEmployee2，它是对CommissionEmployee类的扩展，继承该类，
它试图访问Commission Employee类的private成员，这会导致编译错误，因为子类不能访问超类的private实例变量。

public class BasePlusCommissionEmployee2 extends CommissionEmployee {
    private double baseSalary;
    public BasePlusCommissionEmployee2
            (String name,String ID,double sales,double rate,double salary){
        super(name,ID,sales,rate);//给父类设置变量
        setBaseSalary(salary);
    }

    //==================== setter和getter =========================//
    public void setBaseSalary(double salary){
        baseSalary = (salary<0.0) ? 0.0 : salary;
    }
    public double getBaseSalary(){return baseSalary;}
    //==================== setter和getter =========================//

    public double earnings(){
        //以下代码错误
        //私有变量不能被别的类访问
        return (baseSalary + commissionRate * grossSales);
        //改成getCommissionRate就好了
    }
    public String toString(){
        //以下代码错误
        //私有变量不能被别的类访问
        return String.format("%s:%s\n%s:%s\n%s:%.2f\n%s:%.2f\n%s:%.2f\n",
                "员工姓名", name, "员工工号", ID, "销售额", grossSales, "提成率", commissionRate,
                "基本底薪",baseSalary);
    }
}

第四个例子

如果CommissionEmployee类的实例变量声明为protected，扩展 CommissionEmployee类的BasePlusCornrnissionEmployee3类就可以直接
使用这些数据值。

使用protected实例变量会带来一些潜在的问题。
第一，子类可以不用set方法就为继承变量直接赋值，从而使子类对象可能将无效值赋给继承变量，使对象处于矛盾的状态中。
第二，子类的代码编写很可能依赖于父类的数据操作。
第三，类的protected成员对同一程序包中的所有类都是可见的，通常人们并不希望这样。

public class BasePlusCommissionEmployee3 extends CommissionEmployee_copy{
    //这里的 CommissionEmployee_copy 中的实例变量时protected类型的
    private double baseSalary;
    public BasePlusCommissionEmployee3
            (String name, String ID, double sales,double rate,double salary){
        super(name,ID,sales,rate);
        setBaseSalary(salary);
    }

    //==================== setter和getter =========================//
    public void setBaseSalary(double salary){
        baseSalary = (salary<0.0) ? 0.0 : salary;
    }
    public double getBaseSalary(){return baseSalary;}
    //==================== setter和getter =========================//

    public double earnings(){
        //以下代码正确
        //protected变量可以被别的类访问
        return (baseSalary + commissionRate * grossSales);
    }
    public String toString(){
        //私有变量不能被别的类访问
        return String.format("%s:%s\n%s:%s\n%s:%.2f\n%s:%.2f\n%s:%.2f\n",
                "员工姓名", name, "员工工号",ID, "销售额",grossSales,
                "提成率",commissionRate, "基本底薪",baseSalary);
    }
}

第五个例子，将CommissionEmployee类中的实例变量重新设置为private，以保证良好的软件工程特性。然后，创建一个BasePlusComrnissionEmployee4类扩展CommissionEmployee类，用父类的public方法来操作其中的private实例变量。

public class BasePlusCommissionEmployee4 extends CommissionEmployee{
    private double baseSalary;
    public BasePlusCommissionEmployee4
            (String name,String ID,double sales,double rate,double salary){
        super(name,ID,sales,rate);
        setBaseSalary(salary);
    }

    public double getBaseSalary(){return baseSalary;}
    public void setBaseSalary(double salary){
        this.baseSalary = salary<0.0 ? 0.0 : salary;
    }

    public double earnings(){
        return getBaseSalary() + super.earnings();
    }

    public String toString(){
        return String.format("%s %s\n%s:%.2f","带底薪",super.toString(),
                "底薪",getBaseSalary());
    }
}

测试类

public class BasePlusCommissionEmployeeTest4 {
    public static void main(String args[]){
        BasePlusCommissionEmployee4 employee =
                new BasePlusCommissionEmployee4("小石榴", "891", 1000000,
                .06,1600);
        System.out.println("员工基本情况如下：\n");
        System.out.printf("%s %s\n", "员工姓名",employee.getName());
        System.out.printf("%s %s\n", "员工工号", employee.getID());
        System.out.printf("%s %.2f\n", "销售额",employee.getGrossSales());
        System.out.printf("%s %.2f\n", "提成率 ",employee.getCommissionRate());
        System.out.printf("%s %.2f\n", "底薪",employee.getBaseSalary());
        System.out.printf("%s %.2f\n", "员工工资",employee.earnings());
        employee.setGrossSales(2000);
        System.out.printf("\n%s:\n\n%s\n","更新以后员工信息", employee.toString());
        System.out.printf("%s %.2f\n", "员工工资",employee.earnings());
        }
}

运行结果：