红色代码部分是什么意思?

不要那一段代码也能运行,也不报错,但是我看他们都加了这段代码

新手求问红色那段代表什么

class count
    {
        private double x;
        private double y;
        public count(double m,double n)
        {
            x = m;
            y = n;
        }
        public double Distance(double x, double y)
        {
            double dis;
            dis =Math.Sqrt((x+1)*(x+1)+(y+1)*(y+1));
            return dis;
        }
    }

可是去掉也正确

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