code: public static <K> NumberMap<K, Short> newShortMap() {
  		return new NumberMap<K, Short>() {
  			@Override
  			public void add(K key, Short addend) {
  				put(key, containsKey(key) ? (short) (get(key) + addend) : addend);
  			}
  			@Override
  			public void sub(K key, Short subtrahend) {
  				put(key, (short)((containsKey(key) ? get(key) : 0) - subtrahend));
  			}
  		};
  	}
docs: Creates a NumberMap for Shorts.
  
  @param <K>
  @return NumberMap<K>