Arraylist有关问题

import java.util.ArrayList;import java.util.Iterator;import java.util.List;class Student{        private Boolean sex;    private int age;    private String name;        public Boolean getSex() {        return sex;    }    public void setSex(Boolean sex) {        this.sex = sex;    }    public int getAge() {        return age;    }    public void setAge(int age) {        this.age = age;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }        }public class listTest {    /**     * @param args     */    public static void main(String[] args) {        List al = new ArrayList();                Student std = new Student();        std.setAge(10);        std.setName("zhangsan");        std.setSex(true);                Student std1 = new Student();        std.setAge(20);        std.setName("lishi");        std.setSex(true);                Student std2 = new Student();        std.setAge(19);        std.setName("wangwu");        std.setSex(true);                al.add(std);        al.add(std1);        al.add(std2);                                for(Iterator ite = al.iterator();ite.hasNext();){            Student s = (Student)ite.next();            System.out.println(s.getAge()+"--"+s.getName()+"--"+s.getSex());        }    }}