import com.google.common.collect.ImmutableList;

import io.reactivex.rxjava3.core.Observable;

import io.reactivex.rxjava3.core.ObservableTransformer;

public class Ch9_01b {

public static void main(String[] args) {

Observable.just("Alpha", "Beta", "Gamma", "Delta", "Epsilon")

.compose(toImmutableList())

.subscribe(System.out::println);

Observable.range(1, 10)

.compose(toImmutableList())

.subscribe(System.out::println);

}

private static <T> ObservableTransformer<T, ImmutableList<T>> toImmutableList() {

return upstream ->

upstream.collect(ImmutableList::<T> builder, ImmutableList.Builder::add)

.map(ImmutableList.Builder::build)

.toObservable(); // must turn Single into Observable

}

}