是否可以在同一个 Class（不是派生类）中覆盖基础 Class 中的方法？

Question

My understanding is that it is possible to Override a method (marked as Virtual ) in a base class from a derived class using the keywords override .

But what about overriding a method in the same class?

In my specific case, I have a class x with 2 methods. Method a has some common behavior with b , and b adds functionality to method a .

In the past, I have duplicated the code of a in b and added the new functionality into b .

I would like to know if there is a better approach so I can centralize the behavior of method a .

    public class x
    {
       public static void a() {}
       public static void b() {}         
    }

Answer 1

You could simply call your method a() from within your method b() . No need (and no way) to override a method.

public class x
{
   private static int _i = 0;

   public static void a() {
       _i = 1;
   }
   public static void b() {
       a();
       // here is _i = 1;
   }         
}

On the other hand you could have parameter overloads for your method.

public class x
{
   private static int _i = 0;

   public static void a() {
       a(1);
   }
   public static void a(int i) {
      _i = t;
      // common code which can use _i
   }         
}

In this case you can call a(1) or a() with the same result.

Answer 2

You can't override in the same class, you only do that in the derived class. You could put the common behavior of your method in method a and then call it from method b.

public static void a() 
{
// some common functionality
}

public static void b()
{
// do something
a(); //call a
//do something else
}

You're free to call a from within b as many times as needed.

Answer 3

For my understanding it is possible to Override a method (marked as Virtual) in a base class from a derived class using the keywords override. But what about the same override a method in the same class?

You cannot do this. Virtual methods are for Polymorphism , which is a fancy way of saying:

If you write a method that takes a base class, and pass it a derived class, and that method calls a method on the base class, it will actually call the derived implementation.

class A
{
    public virtual void DoSomething() { Console.WriteLine("From A"); }
}

class B : A
{
    public override void DoSomething() { Console.WriteLine("From B"); }
}

class C
{
    public void DoSomethingMagic(A someClassInstance)
    {
        someClassInstance.DoSomething();
    }
}

class Program
{
    public static void Main(string[] args)
    {
        A a = new A();
        B b = new B();
        C c = new C();
        c.DoSomethingMagic(a); // Prints "From A"
        c.DoSomethingMagic(b); // Prints "From B", even though it takes an A

        A bIsAnA = new B();
        c.DoSomethingMagic(bIsAnA); // Prints "From B", because B is also an A
    }
}

With that definition, it makes no sense to try to "override" a method within the same class.

In my specific case I have a Class x with 2 methods, method a as some common behavior with b, and b add functionality to method a.

Just call a() from b() :

public class x
{
   public static void a()
   {
       // "base" implementation here
   }

   public static void b()
   {
       a();
       // extra implementation here
   }
}

Answer 4

Why don't you just call a() from b() ?

public static void b()
{
    // Do some stuff
    a(); // Do the common stuff
    // Do more stuff
}

Answer 5

You split the common part into a third shared but private method.

Answer 6

If I understand correctly your problem is that method b has the same code as method a plus some more code. Something like

public class x
{
    public void a()
    {
        // a code
    }

    public void b()
    {
        // a code

        // b code
    }
}

if that is the case you could call method a in method b like this

class x
{
    public void a()
    {
        // a code
    }

    public void b()
    {
        a();

        // b code
    }
}

The other case is that you have common code to both methods:

class x
{
    public void a()
    {
        // common code

        // a exclusive code
    }

    public void b()
    {
        // common code

        // b exclusive code
    }
}

Then you could extract that code to another method like this:

class x
{
    public void a()
    {
        CommonMethod();

        // a exclusive code
    }

    public void b()
    {
        CommonMethod();

        // b exclusive code
    }

    private void CommonMethod()
    {
        // common code
    }
}

And about overriding a method in the same class. It is called method overloading but it works allowing you to create several methods with the same name which differ from each other in terms of the type of the input.

Like this

class x
{
    public string a(int i)
    {
    }

    public string a(string s)
    {
    }
}

The only restriction is that the methods must have the same return type (string in this example).