Java中遍历Map的两种方法：keySet和entrySet

  //方法一  
  Set<String> set = map.keySet();   
  for (String s:set) {  
   System.out.println(s+","+map.get(s));  
  }  
  //方法二:将Map集合中的映射关系(Map.Entry类型的)取出，存入到Set集合中  
  Set<Map.Entry<String, String>> entryseSet=map.entrySet();  
  for (Map.Entry<String, String> entry:entryseSet) {  
   System.out.println(entry.getKey()+","+entry.getValue());  
  }  

　　

import java.util.Calendar;
import java.util.Date;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map.Entry;

/**
 * 测试keySet()与entrySet()的迭代时间
 * keySet():迭代后只能通过get()取key
 * entrySet()：迭代后可以e.getKey()，e.getValue()取key和value。返回的是Entry接口
 * 最后说明下keySet()的速度比entrySet()慢了很多。看来以后要考虑用entrySet()了
 * @author JackeenLiu
 * @date 2014-4-14 星期一
 */
public class HashMapTest         
{
        public static void main(String[] args) 
        {
                HashMap<String,String> kmap = new HashMap<String,String>();
                HashMap<String, String> emap = new HashMap<String, String>();
                
                //装数据
                for (int i = 0; i < 100; i++) 
                {
                        kmap.put(""+i, "abcdefghijklmnopqrstuvwxyz");
                }
                for (int i = 0; i < 100; i++) 
                {
                        emap.put(""+i, "abcdefghijklmnopqrstuvwxyz");
                }
                
                long stimes = System.currentTimeMillis();
                long ctimes = Calendar.getInstance().getTimeInMillis();
                long dtimes = new Date().getTime();
                
                //初始时间 这里我用了三种取值方式 最后发现System.currentTimeMillis();是最直接的取值方法
                System.out.println(stimes+"        "+ctimes+"        "+dtimes);
                
                Iterator<String> ktor = kmap.keySet().iterator();
                while(ktor.hasNext())
                {
                        System.out.println(ktor.next());
                }
                
                long stimes1 = System.currentTimeMillis();
                long ctimes1 = Calendar.getInstance().getTimeInMillis();
                long dtimes1 = new Date().getTime();
                
                //结束世界并且也是entrySet的开始时间
                System.out.println((stimes1-stimes)+"        "+(ctimes1-ctimes)+"        "+(dtimes1-dtimes));
                System.out.println(stimes1+"        "+ctimes1+"        "+dtimes1);
                
                Iterator<Entry<String, String>> itor = emap.entrySet().iterator();
                while(itor.hasNext())
                {
                        Entry<String, String> e = itor.next();
                        //System.out.println(e.getKey());
                        System.out.println(e.getValue());
                }
                
                long stimes2 = System.currentTimeMillis();
                long ctimes2 = Calendar.getInstance().getTimeInMillis();
                long dtimes2 = new Date().getTime();
                System.out.println(stimes2+"        "+ctimes2+"        "+dtimes2);
                System.out.println((stimes2-stimes1)+"        "+(ctimes2-ctimes1)+"        "+(dtimes2-dtimes1));
        }
}