How to force sub classes to implement a method

You can have abstract methods in a class with other methods that are implemented. The advantage over an interface is that you can include some code with your class and have the new object be forced to fill in the details for the abstract methods.

public abstract class YourClass
{
    // Your class implementation

    public abstract void DoSomething(int x, int y);

    public void DoSomethingElse(int a, string b)
    {
        // You can implement this here
    }
}