predprey

代码说明：

  模拟岛上的生态系统，有陆地生物和鸟类，但是不包含地底生物。 (Predator-Prey Simulation four classes are defined: animal, predator, prey, and island where island is where the simulation is taking place, i.e. where the predator and prey interact (live). A list of predators and prey are instantiated, and then their breeding, eating, and dying are simulted.)