跪求大神帮忙指正我的代码还有哪些地方需要改进

图形类

package com.chy3.practice;

public abstract class Shape {

public abstract String square(double a,double b);

public abstract String circumFerence(double a,double b);

}

矩形类

package com.chy3.practice;

import java.util.Scanner;

public class Rectangle extends Shape {

Scanner input = new Scanner(System.in);

public void cal(){

System.out.println("计算矩形周长和面积");

System.out.println("请输入两条边长");

double stre1 = input.nextDouble();

double stre2 = input.nextDouble();

System.out.println("周长为：  "+circumFerence(stre1, stre2));

System.out.println("面积为：  "+square(stre1, stre2));

}

@Override

public String square(double a,double b) {

// TODO Auto-generated method stub

double squ = a*b;

return "矩形面积为："+squ;

}

@Override

public String circumFerence(double a,double b) {

// TODO Auto-generated method stub

double cif = (a+b)*2;

return "矩形周长为"+cif;

}

}

圆形类

package com.chy3.practice;

import java.lang.Math;

import java.util.Scanner;

public class Circle extends Shape {

Scanner input = new Scanner(System.in);

Double p = Math.PI;

public void cal(){

System.out.println("计算圆形的周长和面积");

System.out.println("请输入半径和直径");

double r = input.nextDouble();

double d = input.nextDouble();

System.out.println("周长为：  "+circumFerence(r, d));

System.out.println("面积为：  "+square(r, d));

}

@Override

public String square(double a,double b) {

// TODO Auto-generated method stub

double squ = p*a*a;

return "圆的面积为"+squ;

}

@Override

public String circumFerence(double a,double b) {

// TODO Auto-generated method stub

double cif = 2*p*b;

return "圆的周长为"+cif;

}

}

实现类

package com.chy3.practice;

public class Initial {

public static void main(String[] args){

System.out.println("计算开始：");

Rectangle rec = new Rectangle();

rec.cal();

Circle cir = new Circle();

cir.cal();

}

}