[转]Java中HashMap遍历的两种方式原文地址: http://www.javaweb.cc/language/java/032291.shtml第一种: Map map = new HashMap(); Iterator iter = map.entrySet().iterator(); while (iter.hasNext()) { Map.Entry entry = (Map.Entry) iter.next(); Object key = entry.getKey(); Object val = entry.getValue(); } 效率高,以后一定要使用此种方式！第二种: Map map = new HashMap(); Iterator iter = map.keySet().iterator(); while (iter.hasNext()) { Object key = iter.next(); Object val = map.get(key); } 效率低,以后尽量少使用！ HashMap的遍历有两种常用的方法，那就是使用keyset及entryset来进行遍历，但两者的遍历速度是有差别的，下面请看实例： public class HashMapTest { public static void main(String[] args) ...{ HashMap hashmap = new HashMap(); for (int i = 0; i < 1000; i ) ...{ hashmap.put("" i, "thanks"); } long bs = Calendar.getInstance().getTimeInMillis(); Iterator iterator = hashmap.keySet().iterator(); while (iterator.hasNext()) ...{ System.out.print(hashmap.get(iterator.next())); } System.out.println(); System.out.println(Calendar.getInstance().getTimeInMillis() - bs); listHashMap(); } public static void listHashMap() ...{ java.util.HashMap hashmap = new java.util.HashMap(); for (int i = 0; i < 1000; i ) ...{ hashmap.put("" i, "thanks"); } long bs = Calendar.getInstance().getTimeInMillis(); java.util.Iterator it = hashmap.entrySet().iterator(); while (it.hasNext()) ...{ java.util.Map.Entry entry = (java.util.Map.Entry) it.next(); // entry.getKey() 返回与此项对应的键 // entry.getValue() 返回与此项对应的值 System.out.print(entry.getValue()); } System.out.println(); System.out.println(Calendar.getInstance().getTimeInMillis() - bs); } } 对于keySet其实是遍历了2次，一次是转为iterator，一次就从hashmap中取出key所对于的value。而entryset只是遍历了第一次，他把key和value都放到了entry中，所以就快了。Java中HashMap遍历的两种方式(本教程仅供研究和学习，不代表JAVA中文网观点)本篇文章链接地址:http://www.javaweb.cc/language/java/032291.shtml如需转载请注明出自JAVA中文网:http://www.javaweb.cc/
来源：https://www.cnblogs.com/wangcp-2014/p/5859497.html