定義父類為虛方法時需要關鍵字 virtual

子類重寫需要關鍵字 override

示例代碼：

//父類
public class People
{
//虛方法
//VR Virtual Reality 虛擬現實
//AR Augmented Reality 增強現實
public virtual void SayHello()
{
Console.WriteLine("父類打招呼的方法");
}

}

//子類（重寫父類方法）
public class Chinese:People
{
public override void SayHello()
{
Console.WriteLine("你好！");
}
}

//子類
public class American:People
{
public override void SayHello()
{
Console.WriteLine("Hello");
}
}

public static void Main(string[] args)
{
//統一調用
List<People> list = new List<People>()
{
new Chinese(),
new American()
};

People people = new People();
people.SayHello();
foreach (People item in list)
{
item.SayHello();
}
Console.ReadKey();
}

繼承（父類為虛方法以及子類的重寫）