package zxd.work619;import java.util.HashMap;import java.util.Iterator;import java.util.Map;import java.util.Set;public class BookTest {    public static void main(String[] args) {    Book book1 = new Book("八仙过海", "200");    Book book2 = new Book("西游记", "500");    Book book3 = new Book("东游记", "400");    Map
     
       map = new HashMap
      
       ();//创建集合    map.put("1", book1);    map.put("2", book2);    map.put("3", book3);    Set
       
         set = map.keySet();    for (String s : map.keySet()) {        System.out.println(map.get(s));    } 　　//遍历一    for (Book st : map.values()) {        System.out.println();    } 　　//遍历二    for (Map.Entry
        
          book : map.entrySet()) {        System.out.println(book.getKey()+","+book.getValue());    } 　　//遍历三    Iterator i = map.entrySet().iterator();//迭代器的调用    while(i.hasNext()){        Map.Entry
         
           m = (Map.Entry
          
           )i.next(); System.out.println(m); } }} 速度快慢：遍历三 > 遍历二 > 遍历一 输出结果：
          
         
        
       
      
     

3=Students [name=张三, age=22]2=Students [name=张二, age=21]1=Students [name=张一, age=20]5=Students [name=张五, age=24]4=Students [name=张四, age=23]