md/test/demo.java

/*
 * @Description: 
 * @Autor: kindring
 * @Date: 2021-09-15 13:53:34
 * @LastEditors: kindring
 * @LastEditTime: 2021-09-15 13:53:35
 * @LastDescript: 
 */
class Point2 {
  protected double x;
  protected double y;
  Point2(double x, double y) {
    this.x = x; this.y = y;
  }
  public getPos() {
    System.out.println(this.x + " " + this.y);
  }
}

class Point3 extends Point2{
  protected double z;
  Point2(double x, double y, double z) {
    super(x, y); this.z = z;
  }
  public getPos() {
    System.out.println(this.x + " " + this.y + " " + this.z);
  }
}