下面程序编译后执行的结果是______________。 class Dog { private String name; private int age; public int step; Dog(String s,int a) { name=s; age=a; step=0; } public void run(Dog fast) { fast.step++; } } class Test { public static void main (String args[]) { Dog d=new Dog("Tom",3); d.run(d); d.run(d); System.out.println(d.step); } }