Java原来如此-遍历Map的三种方法

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;public class Test
{
public static void main(String[] args)
{
Map<Integer, String> map = new HashMap<Integer, String>();
map.put(1, "a");
map.put(2, "b");
map.put(3, "c");// 第一种方法
// Collection<String> c = map.values();
// Iterator it = c.iterator();
// for (; it.hasNext();)
// {
// System.out.println(it.next());
// }//第二种方法
//Set<Integer> key = map.keySet();
//for (Iterator it = key.iterator(); it.hasNext();)
//{
//Integer s = (Integer) it.next();
//System.out.println(map.get(s));
//}//第三种方法
Set<Map.Entry<Integer, String>> set = map.entrySet();
        for (Iterator<Map.Entry<Integer, String>> it = set.iterator(); it.hasNext();)
        {
            Map.Entry<Integer, String> entry = (Map.Entry<Integer, String>) it.next();
            System.out.println(entry.getKey() + "--->" + entry.getValue());
        }}
}