What are the several ways of map traversal?

There are 4 ways to traverse map, namely: 1. Use for loop to traverse map; 2. Use iteration to traverse map; 3. Use keySet to iterate over map; 4. Use entrySet to traverse map.

Several ways to traverse the map are as follows:

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java code:

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");

Method one, for loop

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

Method two, iteration

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());  
    }

Method three, keySet() iteration

 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);  
    }

Method 4, entrySet() iteration

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

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