简单工厂模式

实例：

实现一个简略的盘算器

UML类图：

实现代码：

public class Operation
    {
        private double _numberA = 0;
        private double _numberB = 0;
        
        /// 数字A
        public double NumberA
        {
            get
            {
                return _numberA;
            }
            set
            {
                _numberA = value;
            }
        }

        /// 数字B
        public double NumberB
        {
            get
            {
                return _numberB;
            }
            set
            {
                _numberB = value;
            }
        }

        /// 得到运算成果
        public virtual double getResult()
        {
            double result = 0; 
            return result;
        }

       
    }public class Opera