在前面创建Student类的基础上，派生一个CollegeStudent类并用之编程
创建Student 类的要求见https://blog.csdn.net/m0_37160376/article/details/80329662
CollegeStudent 类在学生类上增加一个专业（profession）数据属性；方法上增加获得专业和设置专业两个方法。并对超类中的toString( )方法进行重写，使得CollegeStudent类中的toString( )方法除了显示学生类的信息外，还要显示它的专业属性。
编写测试程序的主类。在主类中创建一个Student对象和CollegeStudent对象，并显示或修改这两个对象的属性值。
import java.util.Scanner;
class Student {
private static int count;/*** 班级号*/
private String classNo;
/**
* 年龄
*/
private int age;
/**
* 性别
*/
private char sex;
/**
* 姓名
*/
private String name;
/**
* 学号
*/
private String stuNo;
public Student(String stuNo, String classNo, String name, char sex, int age) {
super();
this.age = age;
this.classNo = classNo;
this.name = name;
this.sex = sex;
this.stuNo = stuNo;
count++;
}
public static int getExsitingStudentCount() {
return count;
}
public String getClassNo() {
return classNo;
}
public void setClassNo(String classNo) {
this.classNo = classNo;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
/**
*
* @return F为男,M为女
*/
public String getSexString() {
return sex == 'F' ? "男" : "女";
}
public char getSex() {
return sex;
}
public void setSex(char sex) {
this.sex = sex;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getStuNo() {
return stuNo;
}
public void setStuNo(String stuNo) {
this.stuNo = stuNo;
}
public String prop(String name, Object value, char sep) {
return sep + name + ":" + value;
}
public String toString() {
String desc = prop("学号", stuNo, '\0');
desc += prop("班号", classNo, ',');
desc += prop("姓名", name, ',');
desc += prop("性别", getSexString(), ',');
desc += prop("年龄", age, ',');
return desc;
}
}
class CollegeStudent extends Student{
private String profession;
public CollegeStudent(String stuNo, String classNo, String name, char sex, int age,String profession){
super(stuNo, classNo, name,sex, age);
this.profession = profession;
}
public String getProfession() {
return profession;
}
public void setProfession(String profession) {
this.profession = profession;
}
@Override
public String toString() {
String desc = prop("专业",profession,',');
return super.toString()+ desc;
}
}
public class e2_4 {
public static void main(String[] args) {
Student s1 = new Student("11111", "1", "Tom", 'F', 20);
Student s2 = new Student("22222", "1", "Mary", 'M', 20);
Student s3 = new CollegeStudent("33333", "1", "Tm", 'F', 10,"电光");
System.out.println(s1);
System.out.println(s2);
System.out.println(s3);
Scanner s = new Scanner(System.in);
System.out.println("修改第一位学生的姓名与年龄（回车结束修改）：");
String str1 = s.next();
int a = s.nextInt();
s1.setName(str1);
s1.setAge(a);
System.out.println("修改完成！");
System.out.println("修改第二位学生的姓名与年龄（回车结束修改）：");
String str2 = s.next();
int b = s.nextInt();
s2.setName(str2);
s2.setAge(b);
System.out.println("修改完成！");
printlnSeparator();
System.out.println("修改后信息：");
println("姓名", s1.getName());
println("年龄", s1.getAge());
println("姓名", s2.getName());
println("年龄", s2.getAge());
printlnSeparator();
System.out.println("年龄较大的是：");
if (s1.getAge() > s2.getAge()) {
System.out.println(s1);
} else
System.out.println(s2);
}
private static void printlnSeparator(){
System.out.println("=============================");
}
public static void println(String prop, Object value) {
System.out.println(prop + "：" + value);
}
}
/*00 i love zhangyan 00*/我自己出现的错误有几个：
1.在创建Student的子类CollegeStudent类的时候，会报错There is no default constructor available…的错误，这是因为CollegeStudent类的构造器要做的第一件事是调用Student类的无参构造器，但是Student类没有， 当我写到CollegeStudent类中的CollegeStudent构造函数时
public CollegeStudent(String stuNo, String classNo, String name, char sex, int age,String profession){
super(stuNo, classNo, name,sex, age);
this.profession = profession;
}super(stuNo, classNo, name,sex, age); 调用了父类的多参数构造器。
2.重写CollegeStudent类中的toString方法时，我直接return desc，然后运行程序时只能返回一个专业，修改后应该是return super.toString()+ desc;