public class Demo{ public static void main(String[] args){ Rectangle re=new Rectangle(); re.seta(2.5); re.setb(2.8); re.comput(); Circle ci=new Circle(); ci.seta(2.5); ci.setb(3.5); ci.comput(); }}abstract class Shapc{ private double a; private double b; public double geta(){ return a; } public void seta(double a){ this.a=a; } public double getb(){ return b; }? public void setb(double b){ this.b=b; } public abstract void comput();}class Rectangle extends Shapc{ public void comput(){ double rectArea=geta()*getb(); double rectPerimeter=(geta()+getb())*2; System.out.println("矩形的周長:"+rectPerimeter+",矩形的面積:"+rectArea); }}class Circle extends Shapc{ public void comput(){ double cirArea=geta()*getb()*getb(); double cirPerimeter=geta()*getb()*2; System.out.println("圓形的周長:"+cirPerimeter+",圓形的面積:"+cirArea); }}