/**
  * 矩形类，继承Shape，实现面积计算
  */
 public class Rectangle extends Shape {
     // 长
     private double length;
     // 宽
     private double width;
     /**
      * 无参构造
      */
     public Rectangle() {}
     /**
      * 带参构造，初始化长和宽
      * @param length 长
      * @param width 宽
      */
     public Rectangle(double length, double width) {
         this.length = length;
         this.width = width;
     }
     /**
      * 实现父类抽象方法，计算矩形面积：长×宽
      * @return 矩形的面积
      */
     @Override
     public double getArea() {
         return length * width;
     }
     // Getter和Setter
     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;
     }
 }