重温new和override关键字

测试1
定义类：

 1     interface ITestClass
    {
        string UserName { get; set; }
    }

    class TestParentClas : ITestClass
    {
        public string UserName
        {
            get;
            set;
        }
    }

    class TestChildClass1 : TestParentClas
    {
        public string UserName
        {
            get;
            set;
        }

    }
测试结果1

        private void TestU()
        {
            TestChildClass1 t1 = new TestChildClass1();
            t1.UserName = "Child";
            
            ITestClass t2 = t1;
            string a1 = t2.UserName;//a1为null

            TestParentClas t3 = t1;
            string a2 = t3.UserName;//a2为null
        }

测试2

    class TestChildClass2 : TestParentClas
    {
        public override string UserName
        {
            get;
            set;
        }
    }

编译错误：cannot override inherited member 'TestParentClas.UserName.set' because it is not marked virtual, abstract, or override

    class TestParentClas : ITestClass
    {
        public virtual string UserName
        {
            get;
            set;
        }
    }

测试2结果：

        private void TestU()
        {
            TestChildClass2 t1 = new TestChildClass2();
            t1.UserName = "Child";
            
            ITestClass t2 = t1;
            string a1 = t2.UserName;//a1为Child

            TestParentClas t3 = t1;
            string a2 = t3.UserName;//a2为Child
        }