Java 多态实现图形面积和周长计算

import java.util.Scanner;

public class Main { public static void main(String[] args) { Scanner scanner = new Scanner(System.in); int code = scanner.nextInt(); Shape shape; switch (code) { case 1: double radius = scanner.nextDouble(); shape = new Circle(radius); break; case 2: double length = scanner.nextDouble(); double width = scanner.nextDouble(); shape = new Rectangle(length, width); break; case 3: double a = scanner.nextDouble(); double b = scanner.nextDouble(); double c = scanner.nextDouble(); shape = new Triangle(a, b, c); break; default: shape = null; break; } if (shape != null) { System.out.printf(".2f .2f", shape.area(), shape.circumference()); } } }

abstract class Shape { public abstract double area();

public abstract double circumference();

}

class Circle extends Shape { private double radius;

public Circle(double radius) {
    this.radius = radius;
}

@Override
public double area() {
    return Math.PI * radius * radius;
}

@Override
public double circumference() {
    return 2 * Math.PI * radius;
}

}

class Rectangle extends Shape { private double length; private double width;

public Rectangle(double length, double width) {
    this.length = length;
    this.width = width;
}

@Override
public double area() {
    return length * width;
}

@Override
public double circumference() {
    return 2 * (length + width);
}

}

class Triangle extends 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;
}

@Override
public double area() {
    double p = (a + b + c) / 2;
    return Math.sqrt(p * (p - a) * (p - b) * (p - c));
}

@Override
public double circumference() {
    return a + b + c;
}

}