计算各种图形的周长（多态）更

Question

定义接口或类 Shape，定义求周长的方法length()。

定义如下类，实现接口Shape或父类Shape的方法。

（1）三角形类Triangle （2）长方形类Rectangle （3）圆形类Circle等。

定义测试类ShapeTest，用Shape接口（或类）定义变量shape，用其指向不同类形的对象，输出各种图形的周长。并为其他的Shape接口实现类提供良好的扩展性。

提示： 计算圆周长时PI取3.14。

输入格式:
输入多组数值型数据（double）；

一行中若有1个数，表示圆的半径；

一行中若有2个数（中间用空格间隔），表示长方形的长度、宽度。

一行中若有3个数（中间用空格间隔），表示三角形的三边的长度。（需要判断三个边长是否能构成三角形）

若输入数据中有0或负数，则不表示任何图形，周长为0。

我的代码：

package com.sxt;
import java.util.Scanner;
public class ShapeTest {

    public static void main(String[] args) {
        // TODO 自动生成的方法存根
        Scanner sc=new Scanner(System.in);
        Shape shape;
        while(sc.hasNextDouble()) {
            double a = sc.nextDouble();
            if (a <= 0) {
                System.out.println("0.00");
                continue;
            }
            if (sc.hasNextDouble()) {//长方形
                double b = sc.nextDouble();
                if (b <= 0) {
                    System.out.println("0.00");
                }
                else {
                    shape = new Rectangle(a,b);
                    System.out.printf("%.2f",shape.length());
                    System.out.println();
                }
            } else if (sc.hasNextDouble()) {//三角形
                double b = sc.nextDouble();
                double c = sc.nextDouble();
                shape = new Triangle(a,b,c);
                System.out.printf("%.2f",shape.length());
                System.out.println();
            }
            else {//圆形
                shape = new Circle(a);
                System.out.printf("%.2f",shape.length());
                System.out.println();
            }
        }
        sc.close();
    }
}
interface Shape {
    double length();
}
class Triangle implements Shape{//三角形
    private double a,b,c;
    public Triangle(double a, double b, double c) {
        this.a=a;
        this.b=b;
        this.c=c;
    }

    public double length() {
        if(a<=0||b<=0||c<=0) {
            return 0;
        }
        else if(a+b<=c||a+c<=b||b+c<=a) {
            return 0;
        }
        else {
            return a+b+c;
        }
    }
}
class Rectangle implements Shape{//长方形
    private double a,b;
    public Rectangle(double a,double b){
        this.a=a;
        this.b=b;
    }
    public double length(){
        if(a<=0||b<=0) {
            return 0;
        }
        else {
            return 2*(a+b);
        }
    }
}
class Circle implements Shape{//圆形
    private double radius;
    public Circle (double radius){
        this.radius=radius;
    }
    public double length() {
        if(radius<=0){
            return 0;
        }
        else {
            return 2*3.14*radius;
        }
    }
}

我的运行结果怎么是这样？

好像只执行了长方形类，怎么修改？
怎么让它实现，我输入几个数字就输出对应图形的周长？

Answer 1

import java.util.Scanner;
class Circle implements Shape{
    double dmyr;
    Circle(){
        dmyr = 0;
    }
    Circle(double dmyr){
        this.dmyr = dmyr;
        if(dmyr <= 0) this.dmyr = 0;
    }
    public double length() {
        return 2 * 3.14 * dmyr;
    }
}
class Rectangle implements Shape{
    double da, db;
    Rectangle(){
        this.da = this.db = 0;
    }
    Rectangle(double da){
        this.da = this.db = 0;
    }
    Rectangle(double da, double db){
        this.da = da;
        this.db = db;
        if(da <= 0 || db <= 0){
            this.da = this.db = 0;
        }
    }
    public double length() {
        return 2 * (da + db);
    }
}
class Triangle implements Shape{
    double da;
    double db;
    double dc;
    Triangle(){
        this.da = this.db = this.dc = 0;
    }
    Triangle(double da){
        this.da = this.db = this.dc = 0;
    }
    Triangle(double da, double db){
        this.da = this.db = this.dc = 0;
    }
    Triangle(double da, double db, double dc){
        this.da = da;
        this.db = db;
        this.dc = dc;
        if(da <= 0 || db <= 0 || dc <= 0 || !(da + db > dc && da + dc > db && db + dc > da)){
            this.da = this.db = this.dc = 0;
        }
    }
    public double length() {
        return da + db + dc;
    }
}
interface Shape{
    double length();
}
public class Main {
    public static void main(String[] args) {
        Scanner dmy = new Scanner(System.in);
        while(dmy.hasNextInt()) {
            double[] l = new double[5];
            String s;
            s = dmy.nextLine();
            String[] str = s.split(" ");
            int cnt = 0;
            for (String value : str) {
                l[cnt++] = Double.parseDouble(value);
            }
            if(cnt == 1){
                Circle C = new Circle(l[0]);
                System.out.printf("%.2f\n", C.length());
            }
            else if (cnt == 2){
                Rectangle r = new Rectangle(l[0], l[1]);
                System.out.printf("%.2f\n", r.length());
            }
            else{
                Triangle t = new Triangle(l[0], l[1], l[2]);
                System.out.printf("%.2f\n", t.length());
            }
        }
    }
}