列举一个学校和多个学生的实例来说明一对多的关系：
代码1----学校类
import java.util.List ;
import java.util.ArrayList ;
public class School{
  private String name ;
  private List<Student> allStudents ;
//泛型指向多个学生
  public School(){
    this.allStudents = new ArrayList<Student>() ;
  }
  public School(String name){
    this() ;
    this.setName(name) ;
  }
  public void setName(String name){
    this.name = name ;
  }
  public String getName(){
    return this.name;    
  }
  public List<Student> getAllStudents(){
    return this.allStudents ;
  }
  public String toString(){
    return "学校名称：" + this.name ;
  }
};
 
代码2----学生类
 
public class Student{
  private String name ;
  private int age ;
  private School school; // 一个学生属于一个学校
  public Student(String name,int age){
    this.setName(name) ;
    this.setAge(age) ;
  }
  public void setSchool(School school){
    this.school = school ;
  }
  public School getSchool(){
    return this.school ;
  }
  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----关系类
import java.util.Iterator ;
public class TestDemo{
  public static void main(String args[]){
    School sch = new School("清华大学") ;  // 定义学校
    Student s1 = new Student("张三",21) ;
    Student s2 = new Student("李四",22) ;
    Student s3 = new Student("王五",23) ;
    sch.getAllStudents().add(s1) ;
    sch.getAllStudents().add(s2) ;
    sch.getAllStudents().add(s3) ;
    s1.setSchool(sch) ;
    s2.setSchool(sch) ;
    s3.setSchool(sch) ;
    System.out.println(sch) ;
    Iterator<Student> iter = sch.getAllStudents().iterator() ;
    while(iter.hasNext()){
      System.out.println("\t|- " + iter.next()) ;
    }
  }
};