圆类

package area20240711;  public class Circle extends Picture{     private double r;     private final double PI = 3.1415926;      public Circle(){}      public Circle(double r) {         this.r = r;     }      public double getR() {         return r;     }      public void setR(double r) {         this.r = r;     }      public double getPI() {         return PI;     }      @Override     public double length() {         return 2 * PI * this.r;     }      @Override     public double area() {         return this.r * this.r * PI;     } } 

        图形类

package area20240711;  public abstract class Picture {     public abstract double length();     public abstract double area(); } 

        矩形类

package area20240711;  public class Rectangle extends Picture{     private double length;     private double width;      public Rectangle(){}      public Rectangle(double length, double width) {         this.length = length;         this.width = width;     }      public double getLength() {         return length;     }      public void setLength(double length) {         this.length = length;     }      public double getWidth() {         return width;     }      public void setWidth(double width) {         this.width = width;     }      @Override     public double length() {         return 2.0 * (this.length + this.width);     }      @Override     public double area() {         return this.length * this.width * 1.0;     } } 

        测试

package area20240711; import java.util.Scanner; public class AreaTest {     public static void main(String[] args) {         Scanner sc = new Scanner(System.in);         // 创建一个矩形         Rectangle rtg = creatRectangle();         System.out.println("长为" + rtg.getLength() + "宽为" + rtg.getWidth()         + "的矩形的周长是" + rtg.length());         System.out.println("长为" + rtg.getLength() + "宽为" + rtg.getWidth()         + "的矩形的面积是" + rtg.area());          // 创建一个圆形         Circle c = creatCircle();         System.out.println("半径为" + c.getR() + "圆的周长是" + c.length());         System.out.println("半径为" + c.getR() + "圆的面积是" + c.area());       }      public static Rectangle creatRectangle () {         Scanner sc = new Scanner(System.in);         System.out.println("请输入矩形的长");         double length = sc.nextDouble();         System.out.println("请输入矩形的宽");         double width = sc.nextDouble();         return new Rectangle(length, width);     }      public static Circle creatCircle() {         Scanner sc = new Scanner(System.in);         System.out.println("请输入圆形的半径");         double r = sc.nextDouble();         return new Circle(r);     } }