gistfile1.java

public class Fetcher {
  
    public Observable<String> fetch() {
      return Observable.just("1","2","3").compose(composer());
      // Compiler error: Incompatible type: required Observable<String>, found Observable<Object>
    }
  
    private <T> Observable.Transformer<T,T> composer() {
        return new Observable.Transformer<T, T>() {
            @Override
            public Observable<T> call(Observable<T> o) {
                return o; // dumbest composer
            }
        };
    }
}