HashMap collection - traversal methods

# HashMap collection - traversal methods

Define good collection:

public static void main(String[] args) {
  Map<String,String> onemap=new HashMap<String,String>();
        map.put("1", "value1");
        map.put("2", "value2");
        map.put("3", "value3");
        map.put("4", "value4");

(1) The first: Recommended, especially when a large capacity (highly recommended)

 System.out.println("\n通过Map.entrySet遍历key和value");  
        for(Map.Entry<String, String> entry: onemap.entrySet())
        {
         System.out.println("Key: "+ entry.getKey()+ " Value: "+entry.getValue());
        }

(2) The second method

System.out.println("\n通过Map.entrySet使用iterator遍历key和value: ");  
        Iterator map1it=onemap.entrySet().iterator();
        while(emap1it.hasNext())
        {
         Map.Entry<String, String> entry=(Entry<String, String>) map1it.next();
         System.out.println("Key: "+entry.getKey()+" Value: "+entry.getValue());
        }
```

  (3) Third: general use, secondary value

 System.out.println("\n通过Map.keySet遍历key和value：");  
        for(String key: onemap.keySet())
        {
         System.out.println("Key: "+key+" Value: "+ onemap.get(key));
        }

  (4) The fourth

System.out.println ( "\ n traversed by Map.values () all value, but can not traverse the Key" );  
         for (String V: onemap.values ()) 
        { 
         System.out.println ( "value of The IS" + V); 
        }

(1) by traversing Map.entrySet key value and output:

Key: 1 Value: value1
Key: 2 Value: value2
Key: 3 Value: value3
Key: 4 Value: value4

(2) using the key value and traversing through Map.entrySet iterator 's output :

Key: 1 Value: value1
Key: 2 Value: value2
Key: 3 Value: value3
Key: 4 Value: value4

(3) traversing the key and value output by Map.keySet:

Key: 1 Value: value1
Key: 2 Value: value2
Key: 3 Value: value3
Key: 4 Value: value4

(4) Map.values ​​() through all value, but can not traverse the output of the key:

The value is value1
The value is value2
The value is value3
The value is value4

I hope you can help us with any questions can comment, time for you to solve.