Hash Map

How to write a Java method that stores the months of the year and the number of days of the corresponding month in a collection class, then goes through the collection and prints the name of the months that only have 30 days 

It contains unique element.
It is an unordered Set.

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;


public class CollectionDemo
{
    public static void main(String[] args)
    {
        HashMap<String, Integer> map=new HashMap<String, Integer>();
        map.put("jan", 31);
        map.put("feb", 28);
        map.put("mar", 31);
        map.put("apr", 30);
        //So on u can add all
        //Now iterate through whili loop
       
        Iterator itr=map.entrySet().iterator();
       
        while (itr.hasNext()) {
            Map.Entry<String, Integer> ob=(Map.Entry<String, Integer>)itr.next();
            if(ob.getValue()==30)
            {
            System.out.println("key->"+ob.getKey());
            System.out.println("value->"+ob.getValue());
            }
       
        }
    }
}

Output:
key->apr
value->30