map collection traversal

public class Test{
     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");
      
      //The first type: commonly used, secondary value
      System.out.println("traverse key and value through Map.keySet: ");
      for (String key : map.keySet()) {
       System.out.println("key= "+ key + " and value= " + map.get(key));
      }
      
      //Second
      System.out.println("Use iterator to traverse key and value through Map.entrySet: ");
      Iterator<Map.Entry<String, String>> it = map.entrySet().iterator();
      while (it.hasNext()) {
       Map.Entry<String, String> entry = it.next();
       System.out.println("key= " + entry.getKey() + " and value= " + entry.getValue());
      }
      
      //The third type: recommended, especially when the capacity is large
      System.out.println("traverse key and value through Map.entrySet");
      for (Map.Entry<String, String> entry : map.entrySet()) {
       System.out.println("key= " + entry.getKey() + " and value= " + entry.getValue());
      }
    
      // fourth
      System.out.println("traverse all values ​​through Map.values(), but not traverse keys");
      for (String v : map.values()) {
       System.out.println("value= " + v);
      }
     }
}