父类封装后之类如何继承修改属性

Question

class phone{ private int cpu; public void setCpu(int x){ this.cpu=x; } public int getCpu(){ return this.cpu; }}class smartphone extends phone{ setCpu(2);/*problem*/ int num=getCpu(); public void out() { System.out.println(num); }}public class telphone{ public static void main(String[] args){ smartphone s1 = new smartphone(); s1.out(); } }问题出在注释的那一行 怎么通过setCpu修改cpu的值呢