迭代器方法：

迭代器的工作原理：

注意：迭代器是指向两个元素之间的位置，如果后面有元素则hasNext()返回真,当我们调用next()方法时，返回黄色的元素，如上图，当我们调用remove方法是要先调用一次next(),调用remove将返回的元素删除.
容器的最大作用实例：

package ArrayList;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;

class ArrayListTest {

    //容器的最大作用
    public static void printElements(Collection c){
        Iterator it = c.iterator();
        while(it.hasNext()){
            System.out.println(it.next());
        }
    }
    public static void main(String[] args)
    {
        ArrayList al = new ArrayList();
        al.add(new Point(3,3));
        al.add(new Point(4,4));
        printElements(al);
    }
}
class Point
{
    int x,y;
    Point(int x,int y){
        this.x = x;
        this.y = y;
    }
    public String toString(){
        return "x=" + x +","+"y=" + y;
    }
}

Collections类
排序：Collections.sort()
（1）自然排寻(natural ordering )；
（2）实现比较器(Comparator)接口。

package ArrayList;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;

class ArrayListTest {

    public static void printElements(Collection<?> c) {
        Iterator<?> it = c.iterator();
        while(it.hasNext()){
            System.out.println(it.next());
        }
    }

    public static void main(String[] args) {
        Student s1 = new Student(5, "xiaoxi");
        Student s2 = new Student(2, "xiaohong");
        Student s3 = new Student(3, "xiaozhu");
        ArrayList<Student> al = new ArrayList<Student>();
        al.add(s1);
        al.add(s2);
        al.add(s3);
        //Collections类进行排序，自然排序
        Collections.sort(al);
        printElements(al);
    }
}

class Student implements Comparable<Object> {
    int num;
    String name;
    Student(int num, String name) {
        this.name = name;
        this.num = num;
    }

    @Override
    public int compareTo(Object arg0) {
        Student s = (Student) arg0;
        //如果当前数比你要比较的数大返回1，小，返回负数
        return num > s.num ? 1 : (num == s.num ? 0 : -1);
    }

    public String toString() {
        return "num=" +num + "， name=" + name;
    }

}

结果

num=2， name=xiaohong
num=3， name=xiaozhu
num=5， name=xiaoxi