We introduced the idea of interface inheritance. When one interface (a "child" interface) extends one (or more) other ("parent") interfaces, the methods specified in the parent interfaces are "inherited" into the child interface, even though they are not explicitly spelled out there. The effect is that a class which implements the child interface must provide definitions for all the methods specified in the child interface, whether explicitly or implicitly (by being inherited). See also the notes from 2007OCT26.