retry when receive specific error

RxRetryWhen.java

package com.example;

import java.io.IOException;
import java.lang.invoke.WrongMethodTypeException;
import java.util.concurrent.TimeUnit;

import rx.Emitter;
import rx.Observable;
import rx.schedulers.Schedulers;

public class MyClass {

    static boolean shouldPass = false;
    static boolean boromirWarn = true;

    public static class Pair<T1, T2> {
        T1 first;
        T2 second;

        public Pair(T1 first, T2 second) {
            this.first = first;
            this.second = second;
        }
    }

    public static void main(String[] args){

        Observable.timer(2, TimeUnit.SECONDS).subscribe(delay -> {
            System.out.println("Gandalf: You shall now pass");
            shouldPass = true;
        });

        Observable<String> walkIntoMordor = Observable.fromEmitter(e ->
        {
            System.out.println("I want to walk into Mordor!");
                if(!shouldPass) {
                    e.onError(new IOException("Gandalf: You shall not pass"));
                    return;
                }

            if(boromirWarn) {
                e.onError(new WrongMethodTypeException("Boromir: One Does Not Simply Walk into Mordor"));
                return;
            }
            e.onNext("Mordor!");
            e.onCompleted();
        }, Emitter.BackpressureMode.NONE);

        walkIntoMordor.retryWhen(e -> e
                .zipWith(Observable.interval(500, TimeUnit.MILLISECONDS), (err, i) -> new Pair<>(err, i))
                .flatMap(k -> {
                    if(k.second == 5)
                        return Observable.error(k.first);

                    if(k.first instanceof IOException) {
                        System.out.println("Waiting for Gandalf");
                        return Observable.just(null);
                    }
                    System.out.println("Boromir should warn you");
                    return Observable.error(k.first);
                })
            )
            .observeOn(Schedulers.newThread())
            .subscribeOn(Schedulers.computation())
            .toBlocking()
            .subscribe(msg ->
            System.out.println("And i passed : " + msg)
         , e -> System.out.println("You won't never pass: " + e.getMessage())
         , () -> System.out.println("I am on my destination!"));



    }

}

/*
                .flatMap(k -> {
                    if(k.second == 5)
                        return Observable.error(k.first);

                    if(k.first instanceof IOException) {
                        System.out.println("Waiting for Gandalf");
                        return Observable.just(null);
                    }
                    System.out.println("Boromir should warn you");
                    return Observable.error(k.first);
                })
            )
 */