3-3 老师帮我看一看我自己跟着老师写的主方法里的代码，

第三行Subject sub1=new Subject("计算机科学与应用","J0001",4 ); 有报错：

the constructure Subject(String String int ) is undefined 为什么会出现这个报错啊？

public static void main(String[] args) {

// TODO Auto-generated method stub

Subject sub1=new Subject("计算机科学与应用","J0001",4 );//第一字写的时候出现错误，原因是进行跨包调用，用import  

                          //括号内利用构造方法对他进行赋值

System.out.println(sub1.info()) ;

System.out.println("======================================");

//

Student stu1=new Student("张三","S01","男",  18);

System.out.println(stu1.introduction());

System.out.println("======================================");

Student stu2=new Student("张三","S01","男",  18);

System.out.println(stu2.introduction("计算机科学与应用专业 ",4)) ;

System.out.println("======================================");

Student stu3=new Student("张三","S01","男",  18);

System.out.println("======================================");

sub1.addStudents(stu1); 

sub1.addStudents(stu2);

sub1.addStudents(stu3);

System.out.println(sub1.getSubjectName()+"的专业中以有"+sub1.getStudentNum()+"个学生报名 ");