code: private void removeMapping(int num) {
  		if (num < numMappings) {
  			System.arraycopy(mappings, num * 2, mappings, (num - 1) * 2, (numMappings - num) * 2);
  		}
  		mappings[numMappings * 2 - 1] = null;
  		mappings[numMappings * 2 - 2] = null;
  		numMappings--;
  	}
docs: num ranges from 1 to numMappings