java 遍历Map 和 根据Map的值（value）取键(key)

public static void main(String[] args) {
//		Map<String, Object> map = new HashMap<String, Object>();
		Map<String, Object> map = new LinkedHashMap<String, Object>();
		map.put("username","zhaokuo");
		map.put("password", "123456");
		map.put("email", "zhaokuo719@163.com");
		map.put("sex", "男");
		
		//第一种 用for循环的方式
		for (Map.Entry<String, Object> m :map.entrySet())  {
			System.out.println(m.getKey()+"\t"+m.getValue());
		}
		
		//利用迭代 （Iterator）
		Set set=map.entrySet();
		Iterator iterator=set.iterator();
		while(iterator.hasNext()){
				Map.Entry<String, Object> enter=(Entry<String, Object>) iterator.next();
				System.out.println(enter.getKey()+"\t"+enter.getValue());
		}
		//利用KeySet 迭代
		Iterator it = map.keySet().iterator();
		while(it.hasNext()){
			 String key;   
		     String value;   
		     key=it.next().toString();   
		     value=(String) map.get(key);   
		     System.out.println(key+"--"+value);   
		}
		//利用EnterySet迭代
		Iterator i=map.entrySet().iterator();          
		System.out.println( map.entrySet().size());   
		String key;          
		String value;   
		while(i.hasNext()){   
		        Map.Entry entry = (Map.Entry)i.next();          
		        key=entry.getKey().toString();          
		        value=entry.getValue().toString();          
		        System.out.println(key+"===="+value);                    
		}  
		
		System.out.println(getKeyByValue(map, "zhaokuo"));
	}

//根据Value取Key
	public static String getKeyByValue(Map map, Object value) {
		String keys="";
		Iterator it = map.entrySet().iterator();
		while (it.hasNext()) {
			Map.Entry entry = (Entry) it.next();
			Object obj = entry.getValue();
			if (obj != null && obj.equals(value)) {
				keys=(String) entry.getKey();
			}


		}
		return keys;
		}