UML question: aren't dotted lines only used for for "implements"?

Hello, I'm studying for my SCJA using McKenzie's book, and I just came across something strange. On page 163, the Full Shapes Class Diagram shows the relationship between Line and Shape using a dotted line (and it uses a dotted line again to represent the relationship between Point and Shape).

However, the "UML for the Java Associate" document that I downloaded from this forum (by the same authors who did Head First Java), says that dotted lines are used when a class implements an interface. It means "implements" rather than "extends".

If you look at the code for Line and Point in McKenzie's book, a few pages before, they clearly "extend" Shape, they don't "implement" it.

Is this a mistake in the book? Or is there another explanation for it?

Thank you for your help!

Hmmmm...Let me check that.

Indeed, Shape is an interface, and classes always implement interfaces, whereas only interfaces can extend interfaces.

Thank you, Cameron. At that point in the book, though, Shape is still a class, right? So shall I just replace the dotted line with a solid line?

Thank you very much for your help, I've only just started learning Java and everything is still pretty new to me. Just wanted to make sure I got it right.