Comment the interface, implementation or both?

I imagine that we all (when we can be bothered!) comment our interfaces. e.g.

/// <summary>
/// Foo Interface
/// </summary>
public interface Foo
{
    /// <summary>
    /// Will 'bar'
    /// </summary>
    /// <param name="wibble">Wibble factor</param>
    void Bar(string wibble);
}

Do you also comment the implementation (which may also be provided to clients, e.g. as part of a a library)? If so how do you manage keeping the two in sync? Or do you just add a 'See interface for documentation' comment?

Thanks

Solution 1:

As a general rule, I use the same DRY (Don't Repeat Yourself) principle as with code:

• on interface, document the interface
• on implementation, document the implementation specifics

Java specific: when documenting the implementation, use {@inheritDoc} tag to "include" javadocs from the interface.

For more information:

• Official javadoc documentation
• Some unofficial advice.

Solution 2:

C# usage:

Interface can look like this:

    /// <summary>
    /// Helper class to access various properties for the current site.
    /// </summary>
    public interface ISiteHelper
    {
        /// <summary>
        /// Gets the site id of the current site
        /// </summary>
        /// <returns>The site id.</returns>
        int GetSiteID();
    }
}

Implementation can look like this:

/// <inheritdoc />
public class SiteHelper: ISiteHelper
{
    /// <inheritdoc />
    public int GetSiteID()
    {
        return CommonRepository.GetSiteID();
    }
}