这道题不难，有一个坑点是Math.tan函数的参数注意单位是rad
这使得我卡了半天，又没按照题目要求写，没全对，鉴借的别人的代码，特此记录
import java.text.DecimalFormat; import java.util.Scanner; abstract class shape { public abstract double getArea(); public abstract double getPerimeter(); } class RPentagon extends shape{ private double a; public double getArea() { return 5*Math.pow(a,2)/(4*Math.tan(36*Math.PI/180)); } public double getPerimeter() { return 5*a; } public RPentagon(double a1){ a=a1; } } public class Main{ public static void main(String[]args){ DecimalFormat df=new DecimalFormat("#.####"); Scanner in=new Scanner(System.in); RPentagon r=new RPentagon(in.nextDouble()); System.out.println(df.format(r.getArea())); System.out.println(df.format(r.getPerimeter())); } }