java:所有东西都是对象，所以根类就是Object

java如何调试？

LinkedList zoo = new LinkedList();Object o = new Dog();Pig p = new Pig();zoo.add(o);zoo.add(new Cat());zoo.add(p);while(zoo.size() > 0) {o = zoo.removeFirst();if(o instanceOf Dog)((Dog)o).bark();if(o instanceOf Cat)((Cat)o).meow();if(o instanceOf Pig)((Pig)o).oink();}