类集的多对多关系

缺乏、安全感 2022-01-09 20:57 225阅读 0赞

例如：一个学生可以选择多个学科，多个学科又可以被不同的学生选学

代码1-----学科类

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 int getCredit()\{  
return this.credit ;  
\}  
public String toString()\{  
return "课程名称：" \+ this.name + "；课程学分：" \+ this.credit ;  
\}  
\};

代码2----学生类

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 "学生姓名：" \+ this.name + "；年龄：" \+ this.age ;  
\}  
\};

代码3----多对多关系

import java.util.Iterator ;  
public class TestMore\{  
public static void main(String args\[\])\{  
Course c1 = new Course( "英语",3 ) ; // 第一门课程   
Course c2 = new Course( "计算机",5) ; // 第二门课程   
Student s1 = new Student( "张三",20) ;  
Student s2 = new Student( "李四",21) ;  
Student s3 = new Student( "王五",22) ;  
Student s4 = new Student( "赵六",23) ;  
Student s5 = new Student( "孙七",24) ;  
Student s6 = new Student( "钱八",24) ;  
// 第一门课程有三个学生参加   
c1.getAllStudents().add(s1) ;  
c1.getAllStudents().add(s2) ;  
c1.getAllStudents().add(s6) ;  
s1.getAllCourses().add(c1) ;  
s2.getAllCourses().add(c1) ;  
s6.getAllCourses().add(c1) ;  
// 第二门课程有六个学生参加   
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) ;  
// 输出一门课程的信息，观察一门课程有多少个学生参加\\   
System.out.println(c1) ;  
Iterator<Student> iter1 = c1.getAllStudents().iterator() ;  
while(iter1.hasNext())\{  
Student s = iter1.next() ;  
System.out.println( "\\t|- " \+ s) ;  
\}  
// 通过学生找到学生参加的课程   
System.out.println(s6) ;  
Iterator<Course> iter2 = s6.getAllCourses().iterator() ;  
while(iter2.hasNext())\{  
Course c = iter2.next() ;  
System.out.println( "\\t|- " \+ c) ;  
\}  
\}  
\};

转载于:https://blog.51cto.com/haiyuanxi/945305