三个类：HeadOffice、BranchOffice、OfficeTest
HeadOffice类代码：

package com.imooc.test;

public class HeadOffice {
    private int monthlySalary; // 月工资
    private String performanceRating; //绩效等级

    public HeadOffice() {
    }

    public HeadOffice(int monthlySalary, String performanceRating) {
        this.monthlySalary = monthlySalary;
        this.performanceRating = performanceRating;
    }

    public int getMonthlySalary() {
        return monthlySalary;
    }

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

    public String getPerformanceRating() {
        return performanceRating;
    }

    public void setPerformanceRating(String performanceRating) {
        this.performanceRating = performanceRating;
    }

    final public void calculationBonus() {
        /*
         * 绩效为 A：奖金 = 月工资 * 90% * 3
           绩效为 B：奖金 = 月工资 * 90% * 2
           绩效为 C：奖金 = 月工资 * 90%
           绩效为 D：奖金 = 月工资 * 90% * 0.5
           绩效为 E：没有奖金
         */
        float bonus = 0; //奖金
        switch (performanceRating) {
            case "A":
                bonus = (float) (monthlySalary * 0.9 * 3);
                break;
            case "B":
                bonus = (float) (monthlySalary * 0.9 * 2);
                break;
            case "C":
                bonus = (float) (monthlySalary * 0.9);
                break;
            case "D":
                bonus = (float) (monthlySalary * 0.9 * 0.5);
                break;
            case "E":
                bonus = 0;
                break;
            default:
                System.out.println("绩效等级输入错误");
        }
        System.out.println("，绩效等级：" + performanceRating + "，奖金：" + bonus + "元");
    }
}

BranchOffice类代码：

package com.imooc.test;

public class BranchOffice extends HeadOffice{
    private String name; //

    public BranchOffice(int monthlySalary, String performanceRating, String name) {
        super(monthlySalary, performanceRating);
        this.name = name;
    }

    public BranchOffice() {
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
    public void name () {
        System.out.print(getName());
    }
}

OfficeTest类代码：

package com.imooc.test;

public class OfficeTest {
    public static void main(String[] args) {
        HeadOffice ho1 = new BranchOffice(8000, "C", "小慕");
        BranchOffice bo1 = (BranchOffice) ho1;
        bo1.name();// 小慕
        ho1.calculationBonus();
        HeadOffice ho2 = new BranchOffice(9000, "A", "大毛");
        BranchOffice bo2 = (BranchOffice) ho2;
        bo2.name(); // 大毛
        ho2.calculationBonus();
    }
}