C#中sealed关键字

C#中sealed关键字

1. sealed关键字

    当对一个类应用 sealed 修饰符时，此修饰符会阻止其他类从该类继承。类似于Java中final关键字。     在下面的示例中，类 B 从类 A 继承，但是任何类都不能从类 B 继承。 2. sealed 修饰方法或属性

    能够允许类从基类继承，并防止它们重写特定的虚方法或虚属性。

    1）sealed是对虚方法或虚属性，也就是同override一起使用，如果不是虚方法或虚属性会报出错误：cannot be sealed because it is not an override

.publicclass D
.{
.    /* ConsoleApplication1.MSFun.Sealed.D.M()'
4.     * cannot be sealed because it is not an override
5.     */
.    public sealed void M() { Console.WriteLine("D.M()"); }
.}

public class D
{
    /* ConsoleApplication1.MSFun.Sealed.D.M()'
     * cannot be sealed because it is not an override
     */
    public sealed void M() { Console.WriteLine("D.M()"); }
}

2）防止子类重写特定的方法或属性

.publicclass A
.{
.    protectedvirtualvoid M() { Console.WriteLine("A.M()"); }
.    protectedvirtualvoid M1() { Console.WriteLine("A.M1()"); }
.}
.
.publicclass B : A
.{
.    protected sealed override void M() { Console.WriteLine("B.M()"); }
.    protected override void M1() { Console.WriteLine("B.M1()"); }
.}
.
.public sealed class C : B
.{
.    /* ConsoleApplication1.MSFun.Sealed.C.M()':
16.     * cannot override inherited member 'ConsoleApplication1.MSFun.Sealed.B.M()'
17.     * because it is sealed */
.    //protected override void M() { Console.WriteLine("C.M()"); }
.
.    protected override void M1() { Console.WriteLine("C.M1()"); }
.}  

public class A
{
    protected virtual void M() { Console.WriteLine("A.M()"); }
    protected virtual void M1() { Console.WriteLine("A.M1()"); }
}

public class B : A
{
    protected sealed override void M() { Console.WriteLine("B.M()"); }
    protected override void M1() { Console.WriteLine("B.M1()"); }
}

public sealed class C : B
{
    /* ConsoleApplication1.MSFun.Sealed.C.M()':
     * cannot override inherited member 'ConsoleApplication1.MSFun.Sealed.B.M()'
     * because it is sealed */
    //protected override void M() { Console.WriteLine("C.M()"); }

    protected override void M1() { Console.WriteLine("C.M1()"); }
}