写出如下程序的输出结果。 class A { 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++; } } public static void main (String args[]) { A a=new A(); Dog d=a.new Dog("Tom",3); d.step=25; d.run(d); System.out.println(d.step); } }