This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
Are you asking why we use both extends and implements? If that's your question, the answer is because this class extends another class and implements an interface.
Or are you asking about why it's in that order? If that's your question, then the answer is because that's the order the author happened to write it in, or perhaps because he had no choice because maybe the spec says it has to be in that order.