简单工厂模式

本程序主要实现加法和减法2种运算，要实现别的运算请扩展该运算方法和修改操作工厂类！

操作类：

 class Operation
    {       
        public double NumberA { get; set; }
        public double NumberB { get; set; }
        public virtual double getResult()
        {
            return 0.0;
        }
    }

    class OperationAdd : Operation
    {
        public override double getResult()
        {
            return NumberA + NumberB;
        }
    }

    class OperationSub : Operation
    {
        public override double getResult()
        {
            return NumberA - NumberB;
        }
    }

　　操作工厂类：

 class OperationFactory
    {
        public static Operation createOperate(string operate)
        {
            Operation o = null;
            switch (operate)
            {
                case "+":
                    o = new OperationAdd();
                    break;
                case "-:":
                    o = new OperationSub();
                    break;
            }
            return o;
        }
    }

　　UI调用实现：

static void Main(string[] args)
{
Operation oper = OperationFactory.createOperate("+");
oper.NumberA = 3;
oper.NumberB = 5;
Console.WriteLine(oper.getResult());

}