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重温new和override关键字

测试1
定义类：

 1     interface ITestClass
 2     {
 3         string UserName { get; set; }
 4     }
 5 
 6     class TestParentClas : ITestClass
 7     {
 8         public string UserName
 9         {
10             get;
11             set;
12         }
13     }
14 
15     class TestChildClass1 : TestParentClas
16     {
17         public string UserName
18         {
19             get;
20             set;
21         }
22 
23     }
测试结果1

 1         private void TestU()
 2         {
 3             TestChildClass1 t1 = new TestChildClass1();
 4             t1.UserName = "Child";
 5             
 6             ITestClass t2 = t1;
 7             string a1 = t2.UserName;//a1为null
 8 
 9             TestParentClas t3 = t1;
10             string a2 = t3.UserName;//a2为null
11         }

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

1     class TestParentClas : ITestClass
2     {
3         public virtual string UserName
4         {
5             get;
6             set;
7         }
8     }

测试2结果：

 1         private void TestU()
 2         {
 3             TestChildClass2 t1 = new TestChildClass2();
 4             t1.UserName = "Child";
 5             
 6             ITestClass t2 = t1;
 7             string a1 = t2.UserName;//a1为Child
 8 
 9             TestParentClas t3 = t1;
10             string a2 = t3.UserName;//a2为Child
11         }

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原文地址：https://www.cnblogs.com/liyongjian/p/3255609.html