From 12.4.1: "When a class is initialized, its superclasses are initialized (if they have not been previously initialized), as well as any superinterfaces (§8.1.5) that declare any default methods (§9.4.3) (if they have not been previously initialized)."

Compare JVMS 5.5: "A class or interface C may be initialized only as a result of ... If C is an interface that declares a non-abstract, non-static method, the initialization of a class that implements C directly or indirectly."

A private interface method is non-abstract and non-static, but it is not a default method. The 12.4.1 description should be updated to include private methods.