import java.util.HashMap;
import java.util.Set;

/*
 * Example of keySet() method.
 */
public class HashMapExample
{
    public static void main( String[] args )
    {

        HashMap<Integer, String> hashMap = new HashMap<Integer, String>();

        hashMap.put(1, "Apple");
        hashMap.put(2, "Ball");
        hashMap.put(3, "Cat");

        System.out.println("hashMap : " + hashMap + "\n");

        /*
         * Returns a Set view of the keys contained in this map. The set is
         * backed by the map, so changes to the map are reflected in the set,
         * and vice-versa. 
         * 
         * If the map is modified while an iteration over the
         * set is in progress (except through the iterator's own remove
         * operation), the results of the iteration are undefined. The set
         * supports element removal, which removes the corresponding mapping
         * from the map, via the Iterator.remove, Set.remove, removeAll,
         * retainAll, and clear operations. It does not support the add or
         * addAll operations.
         */
        Set<Integer> set = hashMap.keySet();

        System.out.println("set : " + set + "\n");

        for( Integer key : set )
        {
            System.out.println(key);
        }

    }
}