Map method with or without “implements”?

Hello

In some books (such as Hadoop, The Definitive Guide) the Mapper method is defined like this:

public class MapClass extends Mapper extends Mapper<...

but in other books (such as Hadoop in Action) is like this:

public static class MapClass extends MapReduceBase implements Mapper <...

Which one is prefered or what's the difference?.
Maybe the first option is newer?.
Why static?.
The same happens with other methods.

Regards