- 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,以後一定要使用此種方式!
第二種:
- Map map = new HashMap();
- Iterator iter = map.keySet().iterator();
- while (iter.hasNext()) {
- Object key = iter.next();
- Object val = map.get(key);
- }
效率低,以後儘量少使用!
例:
HashMap的遍歷有兩種常用的方法,那就是使用keyset及entryset來進行遍歷,但兩者的遍歷速度是有差別的,下面請看實例:
- 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() 返回與此項對應的鍵
- // entry.getValue() 返回與此項對應的值
- System.out.print(entry.getValue());
- }
- System.out.println();
- System.out.println(Calendar.getInstance().getTimeInMillis() - bs);
- }
- }
對於keySet其實是遍歷了2次,一次是轉爲iterator,一次就從hashmap中取出key所對於的value。而entryset只是遍歷了第一次,他把key和value都放到了entry中,所以就快了。
注:Hashtable的遍歷方法和以上的差不多!