如何恰到好处地使用protected

package P162_第一小题;class Student {    protected String name;//如果不用protected，想想会发生什么？    protected int age;//    public Student(String name, int age) {        this.name = name;        this.age = age;    }    public void show() {        System.out.println(name + " 的年龄是 " + age);    }}class Undergraduate extends Student {    private String degree;    public Undergraduate(String name, int age, String degree) {        super(name, age);        this.degree = degree;    }    public void show() {        System.out.println(name + " 的年龄是 " + age + ", 学位是" + degree);    }}public class Test {    public static void main(String[] args) {        new Student("郭浩东", 20).show();        new Undergraduate("郭浩东",20,"本科").show();    }}