Java class set _ example: many-to-many relationship notes

Java class set _ example: many-to-many relationship notes

Instance requirements:

One student can select multiple courses and multiple students can participate in one course. This is a typical multi-to-many relationship.
To complete this program, we should first define two categories: Student for student information and course for course information. There is a collection in one student class to save all the courses, in the course, there must also be a class set that stores all the students.

3. Knowledge Used in this instance

1. List Set
2. Transfer references
3. iterator

4. Details

Course. Java

Import Java. util. list; import Java. util. arraylist; public class course {private string name; private int credit; private list <student> allstudents; Public Course () {This. allstudents = new arraylist <student> ();} public course (string name, int credit) {this (); this. name = Name; this. credit = credit;} public list <student> getallstudents () {return this. allstudents;} public void setname (string name) {This. name = Name;} public void setcredit (INT credit) {This. credit = credit;} Public String getname () {return this. name;} public ITN getcredit () {return this. credit;} Public String tostring () {return "Course name:" + this. name + "; course credits:" + this. credit ;}}

Student. Java

Import Java. util. list; import Java. util. arraylist; public class student {private string name; private int age; private list <course> allcourses; Public student () {This. allcourses = new arraylist <course> ();} public student (string name, int age) {this (); this. name = Name; this. age = age;} public list <course> getallcourses () {return this. allcourses;} public void setname (string name) {This. name = Name;} public void setage (INT age) {This. age = age;} Public String getname () {return this. name;} public int getage () {return this. age;} Public String tostring () {return "Student name:" + this. name + "; age:" + this. age ;}};

Import Java. util. iterator; public class testmore {public static void main (string ARGs []) {course C1 = New Course ("English", 3 ); // first course C2 = New Course ("computer", 5); // second course student S1 = new student ("James", 20 ); student S2 = new student ("Li Si", 21); Student S3 = new student ("Wang Wu", 22); Student S4 = new student ("Zhao Liu", 23 ); student S5 = new student ("Sun Qi", 24); Student S6 = new student ("Qian ba", 24 ); // The first course has three students participating in c1.getallstudents (). add (S1); c1.getallstudents (). add (S2); c1.getallstudents (). add (s6); s1.getallcourses (). add (C1); s2.getallcourses (). add (C1); s6.getallcourses (). add (C1); // The second course has six students attending c2.getallstudents (). add (S1); c2.getallstudents (). add (S2); c2.getallstudents (). add (S3); c2.getallstudents (). add (S4); c2.getallstudents (). add (S5); c2.getallstudents (). add (s6); s1.getallcourses (). add (C2); s2.getallcourses (). add (C2); s3.getallcourses (). add (C2); s4.getallcourses (). add (C2); s5.getallcourses (). add (C2); s6.getallcourses (). add (C2); // output the information of a course and observe how many students participate in the course \ system. out. println (C1); iterator <student> iter1 = c1.getallstudents (). iterator (); While (iter1.hasnext () {student s = iter1.next (); system. out. println ("\ t |-" + S);} // find the student's course system. out. println (s6); iterator <course> iter2 = s6.getallcourses (). iterator (); While (iter2.hasnext () {course c = iter2.next (); system. out. println ("\ t |-" + C );}}};