public static native boolean doSomething(params...);
which gets called by regular Java code.
Can Xposed hook it?
Yes, native methods can be hooked. However, in case this is for an app's code, it has to be done after System.loadLibrary(), otherwise the latter overwrites the hook. Ideally, the framework should take care of this itself, but it's not straight-forward and the has been vey little need for this.