Example of `doOnNext` on simple Reactive Stream

Main.java

import io.reactivex.rxjava3.core.*;

public class Main {
    public static void main(String[] args) throws InterruptedException {
        Flowable.fromArray(1, 2, 3, 4, 5)
                .doOnNext((i) -> System.out.println("1: " + i))
                .map(i -> i + 1)
                .doOnNext((i) -> System.out.println("2: " + i))
                .filter(i -> i % 2 != 0)
                .doOnNext((i) -> System.out.println("3: " + i))
                .map(Integer::toBinaryString)
                .doOnNext(i -> System.out.println("4: " + i))
                .ignoreElements()
                .blockingAwait();
    }
}

Output with comments:

1: 1 // begin processing of 1
2: 2 // end processing of 1
1: 2 // begin processing of 2
2: 3
3: 3
4: 11 // end processing of 2
1: 3 // begin processing of 3
2: 4 // end processing of 3
1: 4 // begin processing of 4
2: 5
3: 5
4: 101 // end processing of 4
1: 5 // begin processing of 5
2: 6  // end processing of 5