Require in Explorer method
npublic Explorer (String name,
n      rooms.Room location,
n      int hitStrength,
n      int stamina) {
n Require.condition(hitStrength >= 0);
n Require.condition(stamina >= 0);
n playerName = name;
n room = location;
n strengthPoints = hitStrength;
n staminaPoints = stamina;
n}