计算各种图形的周长（多态）
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。
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");
continue;
}
else {
shape = new Rectangle(a,b);
System.out.printf("%.2f",shape.length());
}
} 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());
}
else {//圆形
shape = new Circle(a);
System.out.printf("%.2f",shape.length());
}
}
sc.close();
}
}
interface Shape {
double length();
}
class Triangle implements Shape{//三角形
private double a,b,c;
public void 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 void 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 void Circle (double radius){
this.radius=radius;
}
public double length() {
if(radius<=0){
return 0;
}
else {
return 2*3.14*radius;
}
}
}
为什么会有这样的提示？应该怎么更改？
public interface Shape {
double length();
}
public class Circle implements Shape {
private double radius;
public Circle(double radius) {
this.radius = radius;
}
public double length() {
if (radius <= 0) {
// 圆不合法
return 0;
}
return 2 * 3.14 * radius;
}
}
public class Rectangle implements Shape {
private double length;
private double width;
public Rectangle(double length, double width) {
this.length = length;
this.width = width;
}
public double length() {
if (length <= 0 || width <= 0) {
// 长方形不合法
return 0;
}
return 2 * (length + width);
}
}
public class Triangle implements Shape {
private double a;
private double b;
private double c;
public Triangle(double a, double b, double c) {
this.a = a;
this.b = b;
this.c = c;
}
public double length() {
if (a + b <= c || a + c <= b || b + c <= a) {
// 三角形不合法
return 0;
}
return a + b + c;
}
}
public class ShapeTest {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
while (sc.hasNext()) {
double a = sc.nextDouble();
if (a <= 0) {
// 不合法的输入，周长为0
System.out.println(0);
continue;
}
Shape shape;
if (sc.hasNextDouble()) {
// 长方形
double b = sc.nextDouble();
shape = new Rectangle(a, b);
} else if (sc.hasNextDouble()) {
// 三角形
double b = sc.nextDouble();
double c = sc.nextDouble();
shape = new Triangle(a, b, c);
} else {
// 圆形
shape = new Circle(a);
}
System.out.println(shape.length());
}
sc.close();
}
}
java代码：
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
while (scanner.hasNext()) {
double[] input = new double[3];
for (int i = 0; i < input.length; i++) {
input[i] = scanner.nextDouble();
// 如果输入中有0或负数，即不构成任何图形
if (input[i] <= 0) {
System.out.println("0.00");
continue;
}
}
if (input[0] == 0 && input[1] == 0 && input[2] == 0) {
break;
}
Shape shape;
if (input[1] == 0 && input[2] == 0) { // 圆形
shape = new Circle(input[0]);
System.out.printf("%.2f\n", shape.length());
} else if (input[2] == 0) { // 长方形
shape = new Rectangle(input[0], input[1]);
System.out.printf("%.2f\n", shape.length());
} else { // 三角形
if (isValidTriangle(input[0], input[1], input[2])) {
shape = new Triangle(input[0], input[1], input[2]);
System.out.printf("%.2f\n", shape.length());
} else {
System.out.println("0.00");
}
}
}
scanner.close();
}
private static boolean isValidTriangle(double a, double b, double c) {
if (a + b <= c || a + c <= b || b + c <= a) {
return false;
}
return true;
}
}
您可以使用以上代码进行运行和验证。
你的 shape 接口 y 应该单独写一个类吧