Search text in Text File

I tried using this code:

SearchV2Builder searchBuilder = client.files().searchV2Builder(query);
List<String> fileExtensions = Arrays.asList(extensions);
SearchOptions searchOptions = SearchOptions.newBuilder().withFileExtensions(fileExtensions).build();
SearchV2Result searchResult = searchBuilder.withOptions(searchOptions).start();
List<SearchMatchV2> searchMatches = searchResult.getMatches();

but it only searches for text file name and not for the content placed inside it. Suppose i have a word "hello" placed inside my text file named "documents" so if i starts typing "he" then the word "hello" should appear in searches from "documents" file. Is the possible as i am having different text files and that should search in all of the text files before giving me the result