public class Study{    public static void main(String[] args) {        Person p = new Person("小明", 12);        Student s = new Student("小红", 20, 99);        // TODO: 定义PrimaryStudent，从Student继承，新增grade字段:        Student ps = new PrimaryStudent("小军", 9, 100, 5);        System.out.println(ps.getGrade());    }}class Person {    protected String name;    protected int age;    public Person(String name, int age) {        this.name = name;        this.age = age;    }    public String getName() { return name; }    public void setName(String name) { this.name = name; }    public int getAge() { return age; }    public void setAge(int age) { this.age = age; }}class Student extends Person {    protected int score;    public Student(String name, int age, int score) {        super(name, age);        this.score = score;    }    public int getScore() { return score; }}class PrimaryStudent extends Student {    protected int grade;    public PrimaryStudent(String name, int age,int score,int grade){        super(name,age,score);        this.grade=grade;    }    public int getGrade(){return grade;}}