map遍历的三种基础用法

java中遍历MAP的几种方法 
Java代码 
Map<String,String> map=new HashMap<String,String>();    
map.put("username", "qq");    
map.put("passWord", "123");    
map.put("userID", "1");    
map.put("email", "qq@qq.com");   
Map<String,String> map=new HashMap<String,String>(); 
map.put("username", "qq"); 
map.put("passWord", "123"); 
map.put("userID", "1"); 
map.put("email", "qq@qq.com"); 
第一种用for循环 
Java代码

for(Map.Entry<String, String> entry:map.entrySet()){    
     System.out.println(entry.getKey()+"--->"+entry.getValue());    
}

第二种用迭代 
Java代码

Set set = map.entrySet();         
Iterator i = set.iterator();         
while(i.hasNext()){      
     Map.Entry<String, String> entry1=(Map.Entry<String, String>)i.next();    
     System.out.println(entry1.getKey()+"=="+entry1.getValue());    
}   
用keySet()迭代 
Java代码

Iterator it=map.keySet().iterator();    
while(it.hasNext()){    
     String key;    
     String value;    
     key=it.next().toString();    
     value=map.get(key);    
     System.out.println(key+"--"+value);    
}

第三种用entrySet()迭代 
Java代码

Iterator it=map.entrySet().iterator();           
System.out.println( map.entrySet().size());    
String key;           
String value;    
while(it.hasNext()){    
        Map.Entry entry = (Map.Entry)it.next();           
        key=entry.getKey().toString();           
        value=entry.getValue().toString();           
        System.out.println(key+"===="+value);                     
}