JAVA遍历Map所有元素.doc

JAVA遍历Map所有元素 2010-03-09 17:18 //JDK1.5???Map map = new HashMap();?????for(Object obj : map.keySet()) {????????? Object key = obj;????????? Object value = map.get(obj);?????}?????//JDK1.4???Map map =??new HashMap()??? ;?????Iterator iter = map.entrySet().iterator();?????while(iter.hasNext()) {????????? Map.Entry entry = (Map.Entry)iter.next();????????? Object key = entry.getKey();????????? Object value = entry.getValue();?????} 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！ 例： 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keyS