计算圆形、矩形周长和面积：用户输入半径，长、宽后再进行计算

生成一个Shape类：

package com.qt;

public abstract class Shape {
    public abstract float permiter();
    public abstract float area();

}

生成一个子类Circle类

package com.qt;

public class Circle extends Shape {
    float r;
    //构造函数，传入半径r
    public Circle(float inpr){
        r=inpr;
    }

    @Override
    public float permiter() {
        // TODO Auto-generated method stub
        float per=(float)(Math.PI*2*r);
        System.out.println("圆形的周长为："+ per);
        return per;
    }

    @Override
    public float area() {
        // TODO Auto-generated method stub
        float area=(float)(Math.PI*r*r);
        System.out.println("圆形的面积为："+ area);
        return area;
    }

}

生成一个子类Rectangle类

package com.qt;

public class Rectangle extends Shape {
    float a,b;
    //构造函数，传入矩形的长和宽
    public Rectangle(float inpa,float inpb){
        a=inpa;
        b=inpb;
    }

    @Override
    public float permiter() {
        // TODO Auto-generated method stub
        float per=(a+b)*2;
        System.out.println("矩形的周长为："+ per);
        return per;
    }

    @Override
    public float area() {
        // TODO Auto-generated method stub
        float area=a*b;
        System.out.println("矩形的面积为："+ area);
        return area;
    }

生成一个含有main函数的类Initial类

package com.qt;
import java.util.Scanner;

public class Initial {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Scanner input=new Scanner(System.in); 
        System.out.println("请输入圆形半径");
        float r=input.nextFloat();
        System.out.println("请输入矩形长");
        float a=input.nextFloat();
        System.out.println("请输入矩形宽");
        float b=input.nextFloat();
        Shape S=new Rectangle(a,b);
        S.area();
        S.permiter();
        Shape S1=new Circle(r);
        S1.area();
        S1.permiter();
    }   
}