这怎么写呀，这是要求，我觉得没错的呀

Question

主要代码
import java.util.Scanner;class Circle {
public double r;
public double get_r(double r){
return r; }
public void set_r(double r) {
this.r= r; }
public double getArea() {
return Math.PIrr; }
public double getPeriometer() {
return 2Math.PIr; }
}
class YuanZhu extends Circle{
private Circle bottom;
private double h;
public YuanZhu() {
super(); }
public YuanZhu(Circle bottom) {
super();
this.bottom = bottom; }
public YuanZhu(double h) {
super();
this.h = h; }
public YuanZhu(Circle bottom,double h) {
super();
this.bottom = bottom;
this.h = h; }
public double getVolume() {
return this.bottom.getArea()*h; }
public double getBiaoMian() {
return this.bottom.getArea()*2+this.bottom.getPeriometer()*h; }}
public class test1 {
public static void main(String[] args) {
double r=10,h=20;
Circle c1 = new Circle();
YuanZhu Y1 = new YuanZhu();
System.out.printf("圆的面积：");
c1.getArea();
System.out.printf("圆的体积：");
c1.getPeriometer();
System.out.printf("圆柱的表面积：");
Y1.getBiaoMian();
System.out.printf("圆柱的体积：");
Y1.getVolume(); }}

getVolume（）函数就不空 getBiaoMian（）怎么就空呢

Answer 1

你得给他赋值啊，没有bottom的值不为空才怪了

public static void main(String[] args) {
        double r=10,h=20;
        Circle c1 = new Circle();
        c1.set_r(r);
         YuanZhu Y1 = new YuanZhu(c1,h);
        System.out.printf("圆的面积："+c1.getArea());

        System.out.printf("圆的体积："+c1.getPeriometer());

        System.out.printf("圆柱的表面积："+ Y1.getBiaoMian());

        System.out.printf("圆柱的体积："+Y1.getVolume());
         }