public static void main(String[] args) {
   Map<String,String> map=new HashMap<String,String>();
   map.put("1", "value1");
   map.put("2", "value2");
   map.put("3", "value3");
   map.put("4", "value4");
   
   //第一种：普通使用，二次取值
   System.out.println("\n通过Map.keySet遍历key和value：");  
   for(String key:map.keySet())
   {
    System.out.println("Key: "+key+" Value: "+map.get(key));
   }
   
   //第二种
   System.out.println("\n通过Map.entrySet使用iterator遍历key和value: ");  
   Iterator map1it=map.entrySet().iterator();
   while(map1it.hasNext())
   {
    Map.Entry<String, String> entry=(Entry<String, String>) map1it.next();
    System.out.println("Key: "+entry.getKey()+" Value: "+entry.getValue());
   }
   
   //第三种：推荐，尤其是容量大时  
   System.out.println("\n通过Map.entrySet遍历key和value");  
   for(Map.Entry<String, String> entry: map.entrySet())
   {
    System.out.println("Key: "+ entry.getKey()+ " Value: "+entry.getValue());
   }
   
   //第四种  
   System.out.println("\n通过Map.values()遍历所有的value，但不能遍历key");  
   for(String v:map.values())
   {
    System.out.println("The value is "+v);
   }
}