HashMap遍历的两种方式，推荐使用entrySet()

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！

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

public class HashMapTest {
	public static void main(String[] args) {
		keySet();
		entrySet();
	}

	public static void keySet() {
		HashMap<Integer,String> hashmap = new HashMap<Integer,String>();
		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.err.println(Calendar.getInstance().getTimeInMillis() - bs);
	}
	
	public static void entrySet() {
		HashMap<Integer,String> hashmap = new HashMap<Integer,String>();
		for (int i = 0; i < 1000; i++) {
			hashmap.put(i, "thanks");
		}
		long bs = Calendar.getInstance().getTimeInMillis();
		Iterator it = hashmap.entrySet().iterator();
		while (it.hasNext()) {
			Entry entry = (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.err.println(Calendar.getInstance().getTimeInMillis() - bs);
	}
}