通过程序设计几何图形、矩形、圆形、正方形、几种类型，能过利用接口和多态性计算几何图形的面积和周长并显示出来

/**利用接口和多态性计算几何图形的面积和周长**/
interface Shape {//声明接口Shape

final float PI = 3.14f; // 定义常量圆周率
abstract void area();//定义抽象方法面积
abstract void perimeter();//定义抽象方法周长
}

class bian {
double width;// 定义变量宽
double length;// 定义变量长
double radius; // 定义变量半径
double S;// 定义变量面积
double C;// 定义变量周长

public bian(double width, double length, double radius) {
this.width = width;
this.length = length;
this.radius = radius;
}
}
class Rectangle extends bian implements Shape {//实现接口
public Rectangle(double width, double length, double radius) {
super(width, length, radius);
}
public void area() {
S = width * length;
System.out.println("矩形面积:" + S);// 输出
}
public void perimeter() {
C = (width + length) * 2;
System.out.println("矩形周长:" + C);// 输出
}
}
class Circle extends bian implements Shape {//实现接口
public Circle(double width, double length, double radius) {
super(width, length, radius);
}

public void area() {
S = PI * radius * radius;
System.out.println("圆形面积:" + S);// 输出
}
public void perimeter() {
C = 2 * PI * radius;
System.out.println("圆形周长:" + C);// 输出
}
}
class Square extends bian implements Shape {//实现接口
public Square(double width, double length, double radius) {
super(width, length, radius);
}

public void area() {
S = width * width;
System.out.println("正方形面积:" + S);// 输出
}

public void perimeter() {
C = (width + width) * 2;
System.out.println("正方形周长:" + C);// 输出
}
}
public class RectCalculate {
public static void main(String[] args) {
Shape p1;//声明接口变量
p1 = new Rectangle(3, 8, 0);//实现类对象赋值接口变量
p1.area();//接口回调
p1.perimeter();//接口回调
p1 = new Circle(0, 0, 2);//实现类对象赋值接口变量
p1.area();
p1.perimeter();
p1 = new Square(8, 0, 0);//实现类对象赋值接口变量
p1.area();
p1.perimeter();
}

}