HashMap的应用

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<String, Book> map = new HashMap<String, Book>();//创建集合
    map.put("1", book1);
    map.put("2", book2);
    map.put("3", book3);
    Set<String> 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<String, Book> 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<Student, Book> m = (Map.Entry<Student, Book>)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]