C#中new, override, virtual的具体用法

一句话：你是否真的了解new, override, virtual

下面代码的结果，如果基类使用接口代替，也是一样的效果。

主要注意看override或new了基类的方法后，调用方将子类对象转型为父类后的输出会有什么不同；

    class Program
    {
        static void Main(string[] args)
        {
            TestShape();
            Console.WriteLine("TestShape   end =============" + Environment.NewLine);
            TestDerive();
            Console.WriteLine("TestDerive  end =============" + Environment.NewLine);
            TestDerive2();
            Console.WriteLine("TestDerive2 end =============" + Environment.NewLine);
            Console.ReadKey();
        }

        private static void TestShape()
        {
            System.Collections.Generic.List<Shape> shapes = new System.Collections.Generic.List<Shape>();
            shapes.Add(new Circle());
            shapes.Add(new Rectangle());
            shapes.Add(new Triangle());
            shapes.Add(new Diamond());
            foreach (Shape s in shapes)
            {
                s.MethodVirtual();
                s.Method();
                Console.WriteLine();
            }

        }

        private static void TestDerive()
        {
            Circle circle = new Circle();
            Rectangle rectangle = new Rectangle();
            Triangle triangel = new Triangle();
            Diamond diamond = new Diamond();
            circle.MethodVirtual();
            circle.Method();
            Console.WriteLine();
            rectangle.MethodVirtual();
            rectangle.Method();
            Console.WriteLine();
            triangel.MethodVirtual();
            triangel.Method();
            Console.WriteLine();
            diamond.MethodVirtual();
            diamond.Method();
            Console.WriteLine();
        }

        private static void TestDerive2()
        {
            Circle circle = new Circle();
            PrintShape(circle);
            Rectangle rectangle = new Rectangle();
            PrintShape(rectangle);
            Triangle triangel = new Triangle();
            PrintShape(triangel);
            Diamond diamond = new Diamond();
            PrintShape(diamond);
            ///out put:
            //circle override MethodVirtual
            //base Method call

            //base MethodVirtual call
            //base Method call

            //base MethodVirtual call
            //base Method call

            //base MethodVirtual call
            //base Method call
        }

        static void PrintShape(Shape sharpe)
        {
            sharpe.MethodVirtual();
            sharpe.Method();
            Console.WriteLine();
        }
    }

    public class Shape
    {
        public virtual void MethodVirtual()
        {
            Console.WriteLine("base MethodVirtual call");
        }

        public void Method()
        {
            Console.WriteLine("base Method call");
        }
    }

    ///类描述：override了基类的virtual方法
    ///
    ///第一种使用方法：转型为父类
    ///sharp s = new Circle()
    ///s.MethodVirtual();
    ///s.Method();
    ///因为子类已经override了父类的MethodVirtual，所以即使子类转型为了sharp，调用的还是子类的方法
    ///out put:
    ///circle override MethodVirtual
    ///base Method call
    ///
    ///第二类使用方法：使用子类本身
    ///这很好理解，全部输出的是子类的方法
    ///Circle circle = new Circle();
    ///circle.MethodVirtual();
    ///circle.Method();
    ///out put: 
    ///circle override MethodVirtual
    ///base Method call
    class Circle : Shape
    {
        public override void MethodVirtual()
        {
            Console.WriteLine("circle override MethodVirtual");
        }
    }

    ///类描述：未做任何处理
    ///
    ///第一种使用方法
    ///sharp s = new Rectangle()
    ///s.MethodVirtual();
    ///s.Method();
    ///out put:
    ///base MethodVirtual call
    ///base Method call
    ///
    ///第二类使用方法：使用子类本身
    ///这很好理解，全部输出的是子类的方法
    ///Rectangle rectangle = new Rectangle();
    ///rectangle.MethodVirtual();
    ///rectangle.Method();
    ///out put:
    ///base MethodVirtual call
    ///base Method call
    class Rectangle : Shape
    {

    }

    ///类描述：new了基类的虚方法即非虚方法
    ///
    ///第一种使用方法
    ///sharp s = new Triangle()
    ///s.MethodVirtual();
    ///s.Method();
    ///因为子类已经new了父类的方法，所以s输出的是父类的方法
    ///out put:
    ///base MethodVirtual call
    ///base Method call
    ///
    ///第二类使用方法：使用子类本身
    ///这很好理解，全部输出的是子类的方法
    ///Triangle triangel = new Triangle();
    ///triangel.MethodVirtual();
    ///triangel.Method();
    ///out put:
    ///triangle new MethodVirtual
    ///triangle new Method
    class Triangle : Shape
    {
        public new void MethodVirtual()
        {
            Console.WriteLine("triangle new MethodVirtual");
        }

        public new void Method()
        {
            Console.WriteLine("triangle new Method");
        }
    }

    ///类描述：创建了基类方法相同的方法，未new及override
    ///编译器会做提示“隐藏继承”，并有如存在 new 关键字一样执行操作
    ///
    ///第一种使用方法
    ///sharp s = new Diamond()
    ///s.MethodVirtual();
    ///s.Method();
    ///因为默认new的效果，所以输出和显式new修饰的一样
    ///out put:
    ///base MethodVirtual call
    ///base Method call
    ///
    ///第二类使用方法：使用子类本身
    ///这很好理解，全部输出的是子类的方法
    ///Diamond diamond = new Diamond();
    ///diamond.MethodVirtual();
    ///diamond.Method();
    ///out put:
    ///Diamond default MethodVirtual
    ///Diamond default Method
    class Diamond : Shape
    {
        public void MethodVirtual()
        {
            Console.WriteLine("Diamond default MethodVirtual");
        }

        public void Method()
        {
            Console.WriteLine("Diamond default Method");
        }
    }