1．基础题分别创建学生类Student和及其子类CollegeStudent根据题意及注释补充所缺代码或完成填空导入正确的包然后在MyApp的入口函数中添加测试代码运行程序程序结果截屏注意所输出的信息应该为自己的信息否则影响实验得分：package cneduseigzhangxiaohu;import javautilDate;public class Student private Strin

package cn.edu.seig.zhangxiaohu; import java.util.Date; public class Student{ private String sname; //姓名 private String sno; //学号 private Date birthDay; //生日

public Student(String sname, String sno, Date birthDay){
    this.sname = sname;
    this.sno = sno;
    this.birthDay = birthDay;
}

public String getSname() {
	return sname;
}
public void setSname(String sname) {
	this.sname = sname;
}
public String getSno() {
	return sno;
}
public void setSno(String sno) {
	this.sno = sno;
}
public Date getBirthDay() {
	return birthDay;
}
public void setBirthDay(Date birthDay) {
	this.birthDay = birthDay;
}

public int getAge() {  
    return (int)((new Date().getTime()-birthDay.getTime())/(1000*3600*24*365));
}

public String toString(){  
	return "学号: "+sno+",姓名: "+sname+",年龄: "+getAge();
}

}

package cn.edu.seig.zhangxiaohu; public class CollegeStudent extends Student { private String major; //专业

public CollegeStudent(String sname, String sno, Date birthDay, String major){
    super(sname, sno, birthDay);
    this.major = major;
}

public String getMajor() {
	return major;
}
public void setMajor(String major) {
	this.major = major;
}
public String toString(){ 
	return super.toString() + "，专业: "+major;
}

}

package cn.edu.seig.zhangxiaohu; import java.util.Date; public class MyApp{ public static void main(String[] args){ System.out.println("=====================我的信息=================="); Date myBirthDay = new Date(2000, 1, 1); CollegeStudent mySelf = new CollegeStudent("张小虎", "2019210001", myBirthDay, "计算机科学与技术"); Student parentObj = mySelf; System.out.println(mySelf.toString()); System.out.println(parentObj.toString()); System.out.println("我的年龄："+mySelf.getAge()); } }

//parentObj = mySelf赋值语句中，parentObj是Student类的上转型对象，对toString函数的调用具有多态性。