Rxjava observable incompatible types

Question

Im trying to return the number of times a word occurs in a text document using rxjava, i keep getting an error saying

incompatible types: Single Long cannot be converted to Observable String 

the function that I'm using is :

static public Observable<String> WordCount(Observable<String> lineEmitter, String startTerm){
    return lineEmitter.flatMap(str -> Observable.fromArray(str.split("\\s")))
            .filter(str -> str.replaceAll("[^a-zA-Z0-9]", "").contains(startTerm))
            .count();
}

I think it is to do with the count at the end making it a single long but I dont know how to convert it to a string

Answer 1

The error is clear, you are using .count() which return Single<Long> and not Observable<String> instead you have to use :

static public Single<Long> wordCount(Observable<String> lineEmitter, String startTerm){
              ^^^^^^^^^^^

Or if you want to get the count as Long you can use .blockingGet()

static public Long WordCount(Observable<String> lineEmitter, String startTerm){
    return lineEmitter.flatMap(str -> Observable.fromArray(str.split("\\s")))
            .filter(str -> str.replaceAll("[^a-zA-Z0-9]", "").contains(startTerm))
            .count()
            .blockingGet();
}

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Advice: Please don't use UpperCase in first letter of method