Classes - The Java Language Specification - page 190

class ColoredPoint extends Point { int color; }
This program causes a compile-time error.
8.1.5. Superinterfaces
The optional implements clause in a class declaration lists the names of interfaces that are
direct superinterfaces of the class being declared.
Interfaces:
implements InterfaceTypeList
InterfaceTypeList:
InterfaceType
InterfaceTypeList , InterfaceType
The following is repeated from § 4.3 to make the presentation here clearer:
ClassType:
TypeDeclSpecifier TypeArguments opt
Each InterfaceType must name an accessible (§ 6.6 ) interface type, or a compile-time error
occurs.
If the TypeName is followed by any type arguments, it must be a correct invocation of the
type declaration denoted by TypeName , and none of the type arguments may be wildcard
type arguments, or a compile-time error occurs.
It is a compile-time error if the same interface is mentioned as a direct superinterface two or
more times in a single implements clause's names. This is true even if the interface is named
in different ways.
Given a (possibly generic) class declaration for C < F 1 ,..., F n > ( n ≥ 0, C ≠ Object ), the direct
superinterfaces of the class type C < F 1 ,..., F n > are the types given in the implements clause of
the declaration of C , if an implements clause is present.
Let C < F 1 ,..., F n > ( n > 0) be a generic class declaration. The direct superinterfaces of the
parameterized class type C < T 1 ,..., T n > , where T i (1 ≤ i ≤ n ) is a type, are all types I < U 1
θ,..., U k θ > , where I < U 1 ,..., U k > is a direct superinterface of C < F 1 ,..., F n > , and θ is the substi-
tution [ F 1 := T 1 ,..., F n := T n ] .