创建了dragon和troll两个对象 分别有攻击伤害和移动步数除此之外还添加了攻击方式 -All monsters should still have a name　however, they should also have an instance variable called spAttackProbability with a default value of 0.2.All monsters must have a special power (via a call to method specialAttack()). A Dragon’s special power is to breath fire, whereas a Troll’s special power is to hit with a club (resulting in a damage of between 1 to 15 points). There is no longer a default method for specialAttack()　however, every subclass of Monster should be forced to provide a method for specialAttack().