用JAVA定义一个people类，包含属性name，sex。为people派生一个之类Eemployee类，为其增加两个属性age和grade。grade分等级A，B，C三个等级。

public class People {
    private String name;
    private String sex;

    public People(String name, String sex) {
        this.name = name;
        this.sex = sex;
    }

    public String getName() {
        return name;
    }

    public String getSex() {
        return sex;
    }
}

public class Employee extends People {
    private int age;
    private String grade;

    public Employee(String name, String sex, int age, String grade) {
        super(name, sex);
        this.age = age;
        this.grade = grade;
    }

    public int getAge() {
        return age;
    }

    public String getGrade() {
        return grade;
    }
}