设计模式-简单工厂模式

构造出一个工厂类，需要使用类型的对象，就返回什么类型的对象
以简单计算器为例
定义运算类，这是个父类，也是抽象类，这个类定义了一个抽象方法

abstract class Operation{
        public abstract double GetResult();
        private double _num1;
        private double _num2;
        public double Num1{
            get { return _num1; }
            set { _num1 = value; }
        }
        public double Num2{
            get { return _num2; }
            set { _num2 = value; }
        }
        public Operation(double num1, double num2){
            this.Num1 = num1;
            this.Num2 = num2;
        }
    }

定义四个子类分别继承这个父类

class OperationForMul : Operation{
        public OperationForMul(double num1, double num2) : base(num1, num2) { }
        public override double GetResult(){
            return this.Num1 * this.Num2;
        }
    }

class OperationForSub : Operation{
        public OperationForSub(double num1, double num2) : base(num1, num2) { }
        public override double GetResult(){
            return this.Num1 - this.Num2;
        }
    }

class OperationForAdd : Operation{
        public OperationForAdd(double num1, double num2) : base(num1, num2) { }
        public override double GetResult(){
            return this.Num1 + this.Num2;
        }
    }

class OperationForDiv : Operation{
        public OperationForDiv(double num1, double num2) : base(num1, num2) { }
        public override double GetResult(){
            if (this.Num2 == 0){
                return 0;
            }return this.Num1 / this.Num2;
        }
    }

定义一个工厂类

public class OperationFactory{
　　public static Operation ReturnOperationItem(string operation, double num1, double num2){
            Operation operationsForOperation = null;
            switch (operation){
                case "+":
                    operationsForOperation = new OperationForAdd(num1, num2);
                    break;
                case "-":
                    operationsForOperation = new OperationForSub(num1, num2);
                    break;
                case "*":
                    operationsForOperation = new OperationForMul(num1, num2);
                    break;
                case "/":
                    operationsForOperation = new OperationForDiv(num1, num2);
                    break;
            }return operationsForOperation;
        }
}

客户端实现

class Program{
        static void Main(string[] args){
            //使用简单工厂模式实现计算器
            Console.WriteLine("输入第一个参与运算的数字");
            double num1 = Convert.ToDouble(Console.ReadLine());
            Console.WriteLine("输入第二个参与运算的数字");
            double num2 = Convert.ToDouble(Console.ReadLine());
            Console.WriteLine("输入一个运算符");
            string strOperation = Console.ReadLine();
            Console.WriteLine(OperationFactory.ReturnOperationItem(strOperation,num1,num2).GetResult());
            Console.ReadKey();
        }
    }

上面的例子也可以用委托来实现，定义一个和工厂类中方法一样的委托，将具体的方法传进去