class Student
{
    protected String name;//姓名
    protected int    age;//年龄 
    private static int num = 0;

    public Student(String name,int age)
    {
        if(name != null)
            this.name = name;
        else
            this.name ="Student " + num++;
        if(age >= 0)
            this.age  = age;
        else
            this.age  = 0;
    }

    public void show()
    {
        System.out.println(this.name + "的年龄是:" + this.age);
    }

}

class Undergraduate extends Student
{
    private  String degree;//学位
    public Undergraduate(String name,int age,String degree)
    {
        super(name,age);
        this.degree = degree;
    }
    public void show()
    {
        System.out.println(this.name + "的年龄是:" + this.age + ",学位是:" + this.degree);
    }

}
public class Test
{
    public static void main(String[] args)
    {
        Student s1 = new Student("小明",23);
        Student s2 = new Student("小米",36);
        Student s3 = new Student("小亮",12);
        Student s4 = new Undergraduate("小红",37,"博士");
        Student s5 = new Undergraduate("小辉",25,"本科");
        
        s1.show();
        s2.show();
        s3.show();
        s4.show();
        s5.show();



    }
}