String fileContent = "";
List<String> wordsList = Arrays.asList(fileContent.trim().split("[\s]+"));

System.out.print(wordsList.size());

1

@Test
    void checkIfWorksWhenNoWord() {
        String emptyString="";

        assertFalse(new WordIterator(emptyString).hasNext());
    }

import java.util.Arrays;
import java.util.Iterator;
import java.util.List;

public class WordIterator implements Iterator {

    int index;
    List<String> wordsList;

    public WordIterator(String fileContent) {
        this.wordsList = Arrays.asList(fileContent.trim().split("[\s]+"));
    }

    public List<String> getWordsList() {
        return wordsList;
    }

    @Override
    public boolean hasNext() {
        return index < wordsList.size();
    }
    @Override
    public String next() {
        if(hasNext()){

            return wordsList.get(index++);
        }
        return null;
    }
}