lsp_example_1.java

class Rectangle{
  public Integer width = 0;
  public Integer height = 0; 

  Rectangle(Integer _width, Integer _height){
    width = _width;
    height = _height; 
  }

  public Integer area(){
    return width * height; 
  }
}

class Square extends Rectangle{
  Square(Integer side){
    super(side, side); 
  }
}