考虑以下两个类:
public class UpByOne {
private int num = 0;
public int getNum () {
return num;
}
public void setNum (int x) {
num = x;
}
public void up () {
num = num + 1;
}
}
class UpByTwo extends UpByOne {
public void up () {
// missing code goes here
}
}
在类UpByTwo中,重定义方法方法up(),使得num加2,以下哪段代码最合适填补省掉的代码?
A.num = num + 2;
B.super.up(); super.up();
C.setNum(getNum()) + 2;
D.super.up() + 1;